1943 lines
76 KiB
C++
1943 lines
76 KiB
C++
//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the primary stateless implementation of the
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// Alias Analysis interface that implements identities (two different
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// globals cannot alias, etc), but does no stateful analysis.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/BasicAliasAnalysis.h"
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#include "llvm/ADT/APInt.h"
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#include "llvm/ADT/ScopeExit.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/CFG.h"
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#include "llvm/Analysis/CaptureTracking.h"
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#include "llvm/Analysis/MemoryBuiltins.h"
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#include "llvm/Analysis/MemoryLocation.h"
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#include "llvm/Analysis/PhiValues.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/Argument.h"
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#include "llvm/IR/Attributes.h"
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#include "llvm/IR/Constant.h"
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#include "llvm/IR/ConstantRange.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GetElementPtrTypeIterator.h"
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#include "llvm/IR/GlobalAlias.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/InstrTypes.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/Operator.h"
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#include "llvm/IR/Type.h"
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#include "llvm/IR/User.h"
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#include "llvm/IR/Value.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/KnownBits.h"
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#include <cassert>
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#include <cstdint>
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#include <cstdlib>
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#include <utility>
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#define DEBUG_TYPE "basicaa"
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using namespace llvm;
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/// Enable analysis of recursive PHI nodes.
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static cl::opt<bool> EnableRecPhiAnalysis("basic-aa-recphi", cl::Hidden,
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cl::init(true));
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/// SearchLimitReached / SearchTimes shows how often the limit of
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/// to decompose GEPs is reached. It will affect the precision
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/// of basic alias analysis.
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STATISTIC(SearchLimitReached, "Number of times the limit to "
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"decompose GEPs is reached");
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STATISTIC(SearchTimes, "Number of times a GEP is decomposed");
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/// Cutoff after which to stop analysing a set of phi nodes potentially involved
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/// in a cycle. Because we are analysing 'through' phi nodes, we need to be
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/// careful with value equivalence. We use reachability to make sure a value
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/// cannot be involved in a cycle.
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const unsigned MaxNumPhiBBsValueReachabilityCheck = 20;
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// The max limit of the search depth in DecomposeGEPExpression() and
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// getUnderlyingObject().
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static const unsigned MaxLookupSearchDepth = 6;
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bool BasicAAResult::invalidate(Function &Fn, const PreservedAnalyses &PA,
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FunctionAnalysisManager::Invalidator &Inv) {
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// We don't care if this analysis itself is preserved, it has no state. But
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// we need to check that the analyses it depends on have been. Note that we
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// may be created without handles to some analyses and in that case don't
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// depend on them.
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if (Inv.invalidate<AssumptionAnalysis>(Fn, PA) ||
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(DT && Inv.invalidate<DominatorTreeAnalysis>(Fn, PA)) ||
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(PV && Inv.invalidate<PhiValuesAnalysis>(Fn, PA)))
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return true;
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// Otherwise this analysis result remains valid.
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return false;
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}
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//===----------------------------------------------------------------------===//
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// Useful predicates
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//===----------------------------------------------------------------------===//
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/// Returns true if the pointer is one which would have been considered an
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/// escape by isNonEscapingLocalObject.
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static bool isEscapeSource(const Value *V) {
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if (isa<CallBase>(V))
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return true;
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// The load case works because isNonEscapingLocalObject considers all
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// stores to be escapes (it passes true for the StoreCaptures argument
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// to PointerMayBeCaptured).
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if (isa<LoadInst>(V))
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return true;
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// The inttoptr case works because isNonEscapingLocalObject considers all
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// means of converting or equating a pointer to an int (ptrtoint, ptr store
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// which could be followed by an integer load, ptr<->int compare) as
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// escaping, and objects located at well-known addresses via platform-specific
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// means cannot be considered non-escaping local objects.
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if (isa<IntToPtrInst>(V))
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return true;
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return false;
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}
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/// Returns the size of the object specified by V or UnknownSize if unknown.
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static uint64_t getObjectSize(const Value *V, const DataLayout &DL,
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const TargetLibraryInfo &TLI,
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bool NullIsValidLoc,
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bool RoundToAlign = false) {
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uint64_t Size;
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ObjectSizeOpts Opts;
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Opts.RoundToAlign = RoundToAlign;
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Opts.NullIsUnknownSize = NullIsValidLoc;
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if (getObjectSize(V, Size, DL, &TLI, Opts))
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return Size;
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return MemoryLocation::UnknownSize;
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}
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/// Returns true if we can prove that the object specified by V is smaller than
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/// Size.
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static bool isObjectSmallerThan(const Value *V, uint64_t Size,
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const DataLayout &DL,
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const TargetLibraryInfo &TLI,
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bool NullIsValidLoc) {
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// Note that the meanings of the "object" are slightly different in the
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// following contexts:
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// c1: llvm::getObjectSize()
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// c2: llvm.objectsize() intrinsic
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// c3: isObjectSmallerThan()
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// c1 and c2 share the same meaning; however, the meaning of "object" in c3
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// refers to the "entire object".
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//
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// Consider this example:
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// char *p = (char*)malloc(100)
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// char *q = p+80;
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//
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// In the context of c1 and c2, the "object" pointed by q refers to the
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// stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
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//
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// However, in the context of c3, the "object" refers to the chunk of memory
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// being allocated. So, the "object" has 100 bytes, and q points to the middle
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// the "object". In case q is passed to isObjectSmallerThan() as the 1st
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// parameter, before the llvm::getObjectSize() is called to get the size of
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// entire object, we should:
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// - either rewind the pointer q to the base-address of the object in
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// question (in this case rewind to p), or
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// - just give up. It is up to caller to make sure the pointer is pointing
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// to the base address the object.
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//
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// We go for 2nd option for simplicity.
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if (!isIdentifiedObject(V))
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return false;
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// This function needs to use the aligned object size because we allow
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// reads a bit past the end given sufficient alignment.
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uint64_t ObjectSize = getObjectSize(V, DL, TLI, NullIsValidLoc,
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/*RoundToAlign*/ true);
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return ObjectSize != MemoryLocation::UnknownSize && ObjectSize < Size;
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}
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/// Return the minimal extent from \p V to the end of the underlying object,
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/// assuming the result is used in an aliasing query. E.g., we do use the query
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/// location size and the fact that null pointers cannot alias here.
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static uint64_t getMinimalExtentFrom(const Value &V,
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const LocationSize &LocSize,
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const DataLayout &DL,
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bool NullIsValidLoc) {
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// If we have dereferenceability information we know a lower bound for the
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// extent as accesses for a lower offset would be valid. We need to exclude
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// the "or null" part if null is a valid pointer. We can ignore frees, as an
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// access after free would be undefined behavior.
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bool CanBeNull, CanBeFreed;
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uint64_t DerefBytes =
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V.getPointerDereferenceableBytes(DL, CanBeNull, CanBeFreed);
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DerefBytes = (CanBeNull && NullIsValidLoc) ? 0 : DerefBytes;
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// If queried with a precise location size, we assume that location size to be
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// accessed, thus valid.
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if (LocSize.isPrecise())
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DerefBytes = std::max(DerefBytes, LocSize.getValue());
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return DerefBytes;
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}
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/// Returns true if we can prove that the object specified by V has size Size.
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static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL,
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const TargetLibraryInfo &TLI, bool NullIsValidLoc) {
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uint64_t ObjectSize = getObjectSize(V, DL, TLI, NullIsValidLoc);
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return ObjectSize != MemoryLocation::UnknownSize && ObjectSize == Size;
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}
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//===----------------------------------------------------------------------===//
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// CaptureInfo implementations
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//===----------------------------------------------------------------------===//
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CaptureInfo::~CaptureInfo() = default;
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bool SimpleCaptureInfo::isNotCapturedBeforeOrAt(const Value *Object,
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const Instruction *I) {
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return isNonEscapingLocalObject(Object, &IsCapturedCache);
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}
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bool EarliestEscapeInfo::isNotCapturedBeforeOrAt(const Value *Object,
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const Instruction *I) {
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if (!isIdentifiedFunctionLocal(Object))
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return false;
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auto Iter = EarliestEscapes.insert({Object, nullptr});
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if (Iter.second) {
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Instruction *EarliestCapture = FindEarliestCapture(
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Object, *const_cast<Function *>(I->getFunction()),
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/*ReturnCaptures=*/false, /*StoreCaptures=*/true, DT, EphValues);
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if (EarliestCapture) {
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auto Ins = Inst2Obj.insert({EarliestCapture, {}});
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Ins.first->second.push_back(Object);
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}
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Iter.first->second = EarliestCapture;
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}
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// No capturing instruction.
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if (!Iter.first->second)
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return true;
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return I != Iter.first->second &&
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!isPotentiallyReachable(Iter.first->second, I, nullptr, &DT, &LI);
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}
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void EarliestEscapeInfo::removeInstruction(Instruction *I) {
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auto Iter = Inst2Obj.find(I);
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if (Iter != Inst2Obj.end()) {
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for (const Value *Obj : Iter->second)
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EarliestEscapes.erase(Obj);
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Inst2Obj.erase(I);
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}
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}
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//===----------------------------------------------------------------------===//
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// GetElementPtr Instruction Decomposition and Analysis
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//===----------------------------------------------------------------------===//
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namespace {
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/// Represents zext(sext(trunc(V))).
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struct CastedValue {
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const Value *V;
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unsigned ZExtBits = 0;
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unsigned SExtBits = 0;
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unsigned TruncBits = 0;
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explicit CastedValue(const Value *V) : V(V) {}
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explicit CastedValue(const Value *V, unsigned ZExtBits, unsigned SExtBits,
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unsigned TruncBits)
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: V(V), ZExtBits(ZExtBits), SExtBits(SExtBits), TruncBits(TruncBits) {}
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unsigned getBitWidth() const {
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return V->getType()->getPrimitiveSizeInBits() - TruncBits + ZExtBits +
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SExtBits;
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}
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CastedValue withValue(const Value *NewV) const {
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return CastedValue(NewV, ZExtBits, SExtBits, TruncBits);
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}
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/// Replace V with zext(NewV)
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CastedValue withZExtOfValue(const Value *NewV) const {
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unsigned ExtendBy = V->getType()->getPrimitiveSizeInBits() -
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NewV->getType()->getPrimitiveSizeInBits();
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if (ExtendBy <= TruncBits)
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return CastedValue(NewV, ZExtBits, SExtBits, TruncBits - ExtendBy);
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// zext(sext(zext(NewV))) == zext(zext(zext(NewV)))
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ExtendBy -= TruncBits;
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return CastedValue(NewV, ZExtBits + SExtBits + ExtendBy, 0, 0);
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}
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/// Replace V with sext(NewV)
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CastedValue withSExtOfValue(const Value *NewV) const {
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unsigned ExtendBy = V->getType()->getPrimitiveSizeInBits() -
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NewV->getType()->getPrimitiveSizeInBits();
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if (ExtendBy <= TruncBits)
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return CastedValue(NewV, ZExtBits, SExtBits, TruncBits - ExtendBy);
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// zext(sext(sext(NewV)))
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ExtendBy -= TruncBits;
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return CastedValue(NewV, ZExtBits, SExtBits + ExtendBy, 0);
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}
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APInt evaluateWith(APInt N) const {
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assert(N.getBitWidth() == V->getType()->getPrimitiveSizeInBits() &&
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"Incompatible bit width");
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if (TruncBits) N = N.trunc(N.getBitWidth() - TruncBits);
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if (SExtBits) N = N.sext(N.getBitWidth() + SExtBits);
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if (ZExtBits) N = N.zext(N.getBitWidth() + ZExtBits);
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return N;
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}
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ConstantRange evaluateWith(ConstantRange N) const {
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assert(N.getBitWidth() == V->getType()->getPrimitiveSizeInBits() &&
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"Incompatible bit width");
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if (TruncBits) N = N.truncate(N.getBitWidth() - TruncBits);
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if (SExtBits) N = N.signExtend(N.getBitWidth() + SExtBits);
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if (ZExtBits) N = N.zeroExtend(N.getBitWidth() + ZExtBits);
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return N;
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}
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bool canDistributeOver(bool NUW, bool NSW) const {
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// zext(x op<nuw> y) == zext(x) op<nuw> zext(y)
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// sext(x op<nsw> y) == sext(x) op<nsw> sext(y)
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// trunc(x op y) == trunc(x) op trunc(y)
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return (!ZExtBits || NUW) && (!SExtBits || NSW);
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}
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bool hasSameCastsAs(const CastedValue &Other) const {
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return ZExtBits == Other.ZExtBits && SExtBits == Other.SExtBits &&
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TruncBits == Other.TruncBits;
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}
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};
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/// Represents zext(sext(trunc(V))) * Scale + Offset.
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struct LinearExpression {
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CastedValue Val;
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APInt Scale;
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APInt Offset;
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/// True if all operations in this expression are NSW.
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bool IsNSW;
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LinearExpression(const CastedValue &Val, const APInt &Scale,
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const APInt &Offset, bool IsNSW)
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: Val(Val), Scale(Scale), Offset(Offset), IsNSW(IsNSW) {}
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LinearExpression(const CastedValue &Val) : Val(Val), IsNSW(true) {
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unsigned BitWidth = Val.getBitWidth();
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Scale = APInt(BitWidth, 1);
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Offset = APInt(BitWidth, 0);
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}
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LinearExpression mul(const APInt &Other, bool MulIsNSW) const {
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// The check for zero offset is necessary, because generally
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// (X +nsw Y) *nsw Z does not imply (X *nsw Z) +nsw (Y *nsw Z).
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bool NSW = IsNSW && (Other.isOne() || (MulIsNSW && Offset.isZero()));
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return LinearExpression(Val, Scale * Other, Offset * Other, NSW);
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}
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};
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}
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/// Analyzes the specified value as a linear expression: "A*V + B", where A and
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/// B are constant integers.
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static LinearExpression GetLinearExpression(
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const CastedValue &Val, const DataLayout &DL, unsigned Depth,
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AssumptionCache *AC, DominatorTree *DT) {
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// Limit our recursion depth.
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if (Depth == 6)
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return Val;
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if (const ConstantInt *Const = dyn_cast<ConstantInt>(Val.V))
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return LinearExpression(Val, APInt(Val.getBitWidth(), 0),
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Val.evaluateWith(Const->getValue()), true);
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if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(Val.V)) {
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if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
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APInt RHS = Val.evaluateWith(RHSC->getValue());
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// The only non-OBO case we deal with is or, and only limited to the
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// case where it is both nuw and nsw.
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bool NUW = true, NSW = true;
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if (isa<OverflowingBinaryOperator>(BOp)) {
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NUW &= BOp->hasNoUnsignedWrap();
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NSW &= BOp->hasNoSignedWrap();
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}
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if (!Val.canDistributeOver(NUW, NSW))
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return Val;
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// While we can distribute over trunc, we cannot preserve nowrap flags
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// in that case.
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if (Val.TruncBits)
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NUW = NSW = false;
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LinearExpression E(Val);
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switch (BOp->getOpcode()) {
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default:
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// We don't understand this instruction, so we can't decompose it any
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// further.
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return Val;
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case Instruction::Or:
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// X|C == X+C if all the bits in C are unset in X. Otherwise we can't
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// analyze it.
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if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), DL, 0, AC,
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BOp, DT))
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return Val;
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LLVM_FALLTHROUGH;
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case Instruction::Add: {
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E = GetLinearExpression(Val.withValue(BOp->getOperand(0)), DL,
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Depth + 1, AC, DT);
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E.Offset += RHS;
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E.IsNSW &= NSW;
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break;
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}
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case Instruction::Sub: {
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E = GetLinearExpression(Val.withValue(BOp->getOperand(0)), DL,
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Depth + 1, AC, DT);
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E.Offset -= RHS;
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E.IsNSW &= NSW;
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break;
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}
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case Instruction::Mul:
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E = GetLinearExpression(Val.withValue(BOp->getOperand(0)), DL,
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Depth + 1, AC, DT)
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.mul(RHS, NSW);
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break;
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case Instruction::Shl:
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// We're trying to linearize an expression of the kind:
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// shl i8 -128, 36
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// where the shift count exceeds the bitwidth of the type.
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// We can't decompose this further (the expression would return
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// a poison value).
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if (RHS.getLimitedValue() > Val.getBitWidth())
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return Val;
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E = GetLinearExpression(Val.withValue(BOp->getOperand(0)), DL,
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Depth + 1, AC, DT);
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E.Offset <<= RHS.getLimitedValue();
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E.Scale <<= RHS.getLimitedValue();
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E.IsNSW &= NSW;
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break;
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}
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return E;
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}
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}
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if (isa<ZExtInst>(Val.V))
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return GetLinearExpression(
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Val.withZExtOfValue(cast<CastInst>(Val.V)->getOperand(0)),
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DL, Depth + 1, AC, DT);
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if (isa<SExtInst>(Val.V))
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return GetLinearExpression(
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Val.withSExtOfValue(cast<CastInst>(Val.V)->getOperand(0)),
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DL, Depth + 1, AC, DT);
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return Val;
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}
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/// To ensure a pointer offset fits in an integer of size IndexSize
|
|
/// (in bits) when that size is smaller than the maximum index size. This is
|
|
/// an issue, for example, in particular for 32b pointers with negative indices
|
|
/// that rely on two's complement wrap-arounds for precise alias information
|
|
/// where the maximum index size is 64b.
|
|
static APInt adjustToIndexSize(const APInt &Offset, unsigned IndexSize) {
|
|
assert(IndexSize <= Offset.getBitWidth() && "Invalid IndexSize!");
|
|
unsigned ShiftBits = Offset.getBitWidth() - IndexSize;
|
|
return (Offset << ShiftBits).ashr(ShiftBits);
|
|
}
|
|
|
|
namespace {
|
|
// A linear transformation of a Value; this class represents
|
|
// ZExt(SExt(Trunc(V, TruncBits), SExtBits), ZExtBits) * Scale.
|
|
struct VariableGEPIndex {
|
|
CastedValue Val;
|
|
APInt Scale;
|
|
|
|
// Context instruction to use when querying information about this index.
|
|
const Instruction *CxtI;
|
|
|
|
/// True if all operations in this expression are NSW.
|
|
bool IsNSW;
|
|
|
|
void dump() const {
|
|
print(dbgs());
|
|
dbgs() << "\n";
|
|
}
|
|
void print(raw_ostream &OS) const {
|
|
OS << "(V=" << Val.V->getName()
|
|
<< ", zextbits=" << Val.ZExtBits
|
|
<< ", sextbits=" << Val.SExtBits
|
|
<< ", truncbits=" << Val.TruncBits
|
|
<< ", scale=" << Scale << ")";
|
|
}
|
|
};
|
|
}
|
|
|
|
// Represents the internal structure of a GEP, decomposed into a base pointer,
|
|
// constant offsets, and variable scaled indices.
|
|
struct BasicAAResult::DecomposedGEP {
|
|
// Base pointer of the GEP
|
|
const Value *Base;
|
|
// Total constant offset from base.
|
|
APInt Offset;
|
|
// Scaled variable (non-constant) indices.
|
|
SmallVector<VariableGEPIndex, 4> VarIndices;
|
|
// Are all operations inbounds GEPs or non-indexing operations?
|
|
// (None iff expression doesn't involve any geps)
|
|
Optional<bool> InBounds;
|
|
|
|
void dump() const {
|
|
print(dbgs());
|
|
dbgs() << "\n";
|
|
}
|
|
void print(raw_ostream &OS) const {
|
|
OS << "(DecomposedGEP Base=" << Base->getName()
|
|
<< ", Offset=" << Offset
|
|
<< ", VarIndices=[";
|
|
for (size_t i = 0; i < VarIndices.size(); i++) {
|
|
if (i != 0)
|
|
OS << ", ";
|
|
VarIndices[i].print(OS);
|
|
}
|
|
OS << "])";
|
|
}
|
|
};
|
|
|
|
|
|
/// If V is a symbolic pointer expression, decompose it into a base pointer
|
|
/// with a constant offset and a number of scaled symbolic offsets.
|
|
///
|
|
/// The scaled symbolic offsets (represented by pairs of a Value* and a scale
|
|
/// in the VarIndices vector) are Value*'s that are known to be scaled by the
|
|
/// specified amount, but which may have other unrepresented high bits. As
|
|
/// such, the gep cannot necessarily be reconstructed from its decomposed form.
|
|
BasicAAResult::DecomposedGEP
|
|
BasicAAResult::DecomposeGEPExpression(const Value *V, const DataLayout &DL,
|
|
AssumptionCache *AC, DominatorTree *DT) {
|
|
// Limit recursion depth to limit compile time in crazy cases.
|
|
unsigned MaxLookup = MaxLookupSearchDepth;
|
|
SearchTimes++;
|
|
const Instruction *CxtI = dyn_cast<Instruction>(V);
|
|
|
|
unsigned MaxIndexSize = DL.getMaxIndexSizeInBits();
|
|
DecomposedGEP Decomposed;
|
|
Decomposed.Offset = APInt(MaxIndexSize, 0);
|
|
do {
|
|
// See if this is a bitcast or GEP.
|
|
const Operator *Op = dyn_cast<Operator>(V);
|
|
if (!Op) {
|
|
// The only non-operator case we can handle are GlobalAliases.
|
|
if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
|
|
if (!GA->isInterposable()) {
|
|
V = GA->getAliasee();
|
|
continue;
|
|
}
|
|
}
|
|
Decomposed.Base = V;
|
|
return Decomposed;
|
|
}
|
|
|
|
if (Op->getOpcode() == Instruction::BitCast ||
|
|
Op->getOpcode() == Instruction::AddrSpaceCast) {
|
|
V = Op->getOperand(0);
|
|
continue;
|
|
}
|
|
|
|
const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
|
|
if (!GEPOp) {
|
|
if (const auto *PHI = dyn_cast<PHINode>(V)) {
|
|
// Look through single-arg phi nodes created by LCSSA.
|
|
if (PHI->getNumIncomingValues() == 1) {
|
|
V = PHI->getIncomingValue(0);
|
|
continue;
|
|
}
|
|
} else if (const auto *Call = dyn_cast<CallBase>(V)) {
|
|
// CaptureTracking can know about special capturing properties of some
|
|
// intrinsics like launder.invariant.group, that can't be expressed with
|
|
// the attributes, but have properties like returning aliasing pointer.
|
|
// Because some analysis may assume that nocaptured pointer is not
|
|
// returned from some special intrinsic (because function would have to
|
|
// be marked with returns attribute), it is crucial to use this function
|
|
// because it should be in sync with CaptureTracking. Not using it may
|
|
// cause weird miscompilations where 2 aliasing pointers are assumed to
|
|
// noalias.
|
|
if (auto *RP = getArgumentAliasingToReturnedPointer(Call, false)) {
|
|
V = RP;
|
|
continue;
|
|
}
|
|
}
|
|
|
|
Decomposed.Base = V;
|
|
return Decomposed;
|
|
}
|
|
|
|
// Track whether we've seen at least one in bounds gep, and if so, whether
|
|
// all geps parsed were in bounds.
|
|
if (Decomposed.InBounds == None)
|
|
Decomposed.InBounds = GEPOp->isInBounds();
|
|
else if (!GEPOp->isInBounds())
|
|
Decomposed.InBounds = false;
|
|
|
|
assert(GEPOp->getSourceElementType()->isSized() && "GEP must be sized");
|
|
|
|
// Don't attempt to analyze GEPs if index scale is not a compile-time
|
|
// constant.
|
|
if (isa<ScalableVectorType>(GEPOp->getSourceElementType())) {
|
|
Decomposed.Base = V;
|
|
return Decomposed;
|
|
}
|
|
|
|
unsigned AS = GEPOp->getPointerAddressSpace();
|
|
// Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
|
|
gep_type_iterator GTI = gep_type_begin(GEPOp);
|
|
unsigned IndexSize = DL.getIndexSizeInBits(AS);
|
|
// Assume all GEP operands are constants until proven otherwise.
|
|
bool GepHasConstantOffset = true;
|
|
for (User::const_op_iterator I = GEPOp->op_begin() + 1, E = GEPOp->op_end();
|
|
I != E; ++I, ++GTI) {
|
|
const Value *Index = *I;
|
|
// Compute the (potentially symbolic) offset in bytes for this index.
|
|
if (StructType *STy = GTI.getStructTypeOrNull()) {
|
|
// For a struct, add the member offset.
|
|
unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
|
|
if (FieldNo == 0)
|
|
continue;
|
|
|
|
Decomposed.Offset += DL.getStructLayout(STy)->getElementOffset(FieldNo);
|
|
continue;
|
|
}
|
|
|
|
// For an array/pointer, add the element offset, explicitly scaled.
|
|
if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
|
|
if (CIdx->isZero())
|
|
continue;
|
|
Decomposed.Offset +=
|
|
DL.getTypeAllocSize(GTI.getIndexedType()).getFixedSize() *
|
|
CIdx->getValue().sextOrTrunc(MaxIndexSize);
|
|
continue;
|
|
}
|
|
|
|
GepHasConstantOffset = false;
|
|
|
|
// If the integer type is smaller than the index size, it is implicitly
|
|
// sign extended or truncated to index size.
|
|
unsigned Width = Index->getType()->getIntegerBitWidth();
|
|
unsigned SExtBits = IndexSize > Width ? IndexSize - Width : 0;
|
|
unsigned TruncBits = IndexSize < Width ? Width - IndexSize : 0;
|
|
LinearExpression LE = GetLinearExpression(
|
|
CastedValue(Index, 0, SExtBits, TruncBits), DL, 0, AC, DT);
|
|
|
|
// Scale by the type size.
|
|
unsigned TypeSize =
|
|
DL.getTypeAllocSize(GTI.getIndexedType()).getFixedSize();
|
|
LE = LE.mul(APInt(IndexSize, TypeSize), GEPOp->isInBounds());
|
|
Decomposed.Offset += LE.Offset.sext(MaxIndexSize);
|
|
APInt Scale = LE.Scale.sext(MaxIndexSize);
|
|
|
|
// If we already had an occurrence of this index variable, merge this
|
|
// scale into it. For example, we want to handle:
|
|
// A[x][x] -> x*16 + x*4 -> x*20
|
|
// This also ensures that 'x' only appears in the index list once.
|
|
for (unsigned i = 0, e = Decomposed.VarIndices.size(); i != e; ++i) {
|
|
if (Decomposed.VarIndices[i].Val.V == LE.Val.V &&
|
|
Decomposed.VarIndices[i].Val.hasSameCastsAs(LE.Val)) {
|
|
Scale += Decomposed.VarIndices[i].Scale;
|
|
Decomposed.VarIndices.erase(Decomposed.VarIndices.begin() + i);
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Make sure that we have a scale that makes sense for this target's
|
|
// index size.
|
|
Scale = adjustToIndexSize(Scale, IndexSize);
|
|
|
|
if (!!Scale) {
|
|
VariableGEPIndex Entry = {LE.Val, Scale, CxtI, LE.IsNSW};
|
|
Decomposed.VarIndices.push_back(Entry);
|
|
}
|
|
}
|
|
|
|
// Take care of wrap-arounds
|
|
if (GepHasConstantOffset)
|
|
Decomposed.Offset = adjustToIndexSize(Decomposed.Offset, IndexSize);
|
|
|
|
// Analyze the base pointer next.
|
|
V = GEPOp->getOperand(0);
|
|
} while (--MaxLookup);
|
|
|
|
// If the chain of expressions is too deep, just return early.
|
|
Decomposed.Base = V;
|
|
SearchLimitReached++;
|
|
return Decomposed;
|
|
}
|
|
|
|
/// Returns whether the given pointer value points to memory that is local to
|
|
/// the function, with global constants being considered local to all
|
|
/// functions.
|
|
bool BasicAAResult::pointsToConstantMemory(const MemoryLocation &Loc,
|
|
AAQueryInfo &AAQI, bool OrLocal) {
|
|
assert(Visited.empty() && "Visited must be cleared after use!");
|
|
|
|
unsigned MaxLookup = 8;
|
|
SmallVector<const Value *, 16> Worklist;
|
|
Worklist.push_back(Loc.Ptr);
|
|
do {
|
|
const Value *V = getUnderlyingObject(Worklist.pop_back_val());
|
|
if (!Visited.insert(V).second) {
|
|
Visited.clear();
|
|
return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal);
|
|
}
|
|
|
|
// An alloca instruction defines local memory.
|
|
if (OrLocal && isa<AllocaInst>(V))
|
|
continue;
|
|
|
|
// A global constant counts as local memory for our purposes.
|
|
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
|
|
// Note: this doesn't require GV to be "ODR" because it isn't legal for a
|
|
// global to be marked constant in some modules and non-constant in
|
|
// others. GV may even be a declaration, not a definition.
|
|
if (!GV->isConstant()) {
|
|
Visited.clear();
|
|
return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal);
|
|
}
|
|
continue;
|
|
}
|
|
|
|
// If both select values point to local memory, then so does the select.
|
|
if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
|
|
Worklist.push_back(SI->getTrueValue());
|
|
Worklist.push_back(SI->getFalseValue());
|
|
continue;
|
|
}
|
|
|
|
// If all values incoming to a phi node point to local memory, then so does
|
|
// the phi.
|
|
if (const PHINode *PN = dyn_cast<PHINode>(V)) {
|
|
// Don't bother inspecting phi nodes with many operands.
|
|
if (PN->getNumIncomingValues() > MaxLookup) {
|
|
Visited.clear();
|
|
return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal);
|
|
}
|
|
append_range(Worklist, PN->incoming_values());
|
|
continue;
|
|
}
|
|
|
|
// Otherwise be conservative.
|
|
Visited.clear();
|
|
return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal);
|
|
} while (!Worklist.empty() && --MaxLookup);
|
|
|
|
Visited.clear();
|
|
return Worklist.empty();
|
|
}
|
|
|
|
static bool isIntrinsicCall(const CallBase *Call, Intrinsic::ID IID) {
|
|
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Call);
|
|
return II && II->getIntrinsicID() == IID;
|
|
}
|
|
|
|
/// Returns the behavior when calling the given call site.
|
|
FunctionModRefBehavior BasicAAResult::getModRefBehavior(const CallBase *Call) {
|
|
if (Call->doesNotAccessMemory())
|
|
// Can't do better than this.
|
|
return FMRB_DoesNotAccessMemory;
|
|
|
|
FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
|
|
|
|
// If the callsite knows it only reads memory, don't return worse
|
|
// than that.
|
|
if (Call->onlyReadsMemory())
|
|
Min = FMRB_OnlyReadsMemory;
|
|
else if (Call->onlyWritesMemory())
|
|
Min = FMRB_OnlyWritesMemory;
|
|
|
|
if (Call->onlyAccessesArgMemory())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees);
|
|
else if (Call->onlyAccessesInaccessibleMemory())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleMem);
|
|
else if (Call->onlyAccessesInaccessibleMemOrArgMem())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleOrArgMem);
|
|
|
|
// If the call has operand bundles then aliasing attributes from the function
|
|
// it calls do not directly apply to the call. This can be made more precise
|
|
// in the future.
|
|
if (!Call->hasOperandBundles())
|
|
if (const Function *F = Call->getCalledFunction())
|
|
Min =
|
|
FunctionModRefBehavior(Min & getBestAAResults().getModRefBehavior(F));
|
|
|
|
return Min;
|
|
}
|
|
|
|
/// Returns the behavior when calling the given function. For use when the call
|
|
/// site is not known.
|
|
FunctionModRefBehavior BasicAAResult::getModRefBehavior(const Function *F) {
|
|
// If the function declares it doesn't access memory, we can't do better.
|
|
if (F->doesNotAccessMemory())
|
|
return FMRB_DoesNotAccessMemory;
|
|
|
|
FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
|
|
|
|
// If the function declares it only reads memory, go with that.
|
|
if (F->onlyReadsMemory())
|
|
Min = FMRB_OnlyReadsMemory;
|
|
else if (F->onlyWritesMemory())
|
|
Min = FMRB_OnlyWritesMemory;
|
|
|
|
if (F->onlyAccessesArgMemory())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees);
|
|
else if (F->onlyAccessesInaccessibleMemory())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleMem);
|
|
else if (F->onlyAccessesInaccessibleMemOrArgMem())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleOrArgMem);
|
|
|
|
return Min;
|
|
}
|
|
|
|
/// Returns true if this is a writeonly (i.e Mod only) parameter.
|
|
static bool isWriteOnlyParam(const CallBase *Call, unsigned ArgIdx,
|
|
const TargetLibraryInfo &TLI) {
|
|
if (Call->paramHasAttr(ArgIdx, Attribute::WriteOnly))
|
|
return true;
|
|
|
|
// We can bound the aliasing properties of memset_pattern16 just as we can
|
|
// for memcpy/memset. This is particularly important because the
|
|
// LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
|
|
// whenever possible.
|
|
// FIXME Consider handling this in InferFunctionAttr.cpp together with other
|
|
// attributes.
|
|
LibFunc F;
|
|
if (Call->getCalledFunction() &&
|
|
TLI.getLibFunc(*Call->getCalledFunction(), F) &&
|
|
F == LibFunc_memset_pattern16 && TLI.has(F))
|
|
if (ArgIdx == 0)
|
|
return true;
|
|
|
|
// TODO: memset_pattern4, memset_pattern8
|
|
// TODO: _chk variants
|
|
// TODO: strcmp, strcpy
|
|
|
|
return false;
|
|
}
|
|
|
|
ModRefInfo BasicAAResult::getArgModRefInfo(const CallBase *Call,
|
|
unsigned ArgIdx) {
|
|
// Checking for known builtin intrinsics and target library functions.
|
|
if (isWriteOnlyParam(Call, ArgIdx, TLI))
|
|
return ModRefInfo::Mod;
|
|
|
|
if (Call->paramHasAttr(ArgIdx, Attribute::ReadOnly))
|
|
return ModRefInfo::Ref;
|
|
|
|
if (Call->paramHasAttr(ArgIdx, Attribute::ReadNone))
|
|
return ModRefInfo::NoModRef;
|
|
|
|
return AAResultBase::getArgModRefInfo(Call, ArgIdx);
|
|
}
|
|
|
|
#ifndef NDEBUG
|
|
static const Function *getParent(const Value *V) {
|
|
if (const Instruction *inst = dyn_cast<Instruction>(V)) {
|
|
if (!inst->getParent())
|
|
return nullptr;
|
|
return inst->getParent()->getParent();
|
|
}
|
|
|
|
if (const Argument *arg = dyn_cast<Argument>(V))
|
|
return arg->getParent();
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
static bool notDifferentParent(const Value *O1, const Value *O2) {
|
|
|
|
const Function *F1 = getParent(O1);
|
|
const Function *F2 = getParent(O2);
|
|
|
|
return !F1 || !F2 || F1 == F2;
|
|
}
|
|
#endif
|
|
|
|
AliasResult BasicAAResult::alias(const MemoryLocation &LocA,
|
|
const MemoryLocation &LocB,
|
|
AAQueryInfo &AAQI) {
|
|
assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
|
|
"BasicAliasAnalysis doesn't support interprocedural queries.");
|
|
return aliasCheck(LocA.Ptr, LocA.Size, LocB.Ptr, LocB.Size, AAQI);
|
|
}
|
|
|
|
/// Checks to see if the specified callsite can clobber the specified memory
|
|
/// object.
|
|
///
|
|
/// Since we only look at local properties of this function, we really can't
|
|
/// say much about this query. We do, however, use simple "address taken"
|
|
/// analysis on local objects.
|
|
ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call,
|
|
const MemoryLocation &Loc,
|
|
AAQueryInfo &AAQI) {
|
|
assert(notDifferentParent(Call, Loc.Ptr) &&
|
|
"AliasAnalysis query involving multiple functions!");
|
|
|
|
const Value *Object = getUnderlyingObject(Loc.Ptr);
|
|
|
|
// Calls marked 'tail' cannot read or write allocas from the current frame
|
|
// because the current frame might be destroyed by the time they run. However,
|
|
// a tail call may use an alloca with byval. Calling with byval copies the
|
|
// contents of the alloca into argument registers or stack slots, so there is
|
|
// no lifetime issue.
|
|
if (isa<AllocaInst>(Object))
|
|
if (const CallInst *CI = dyn_cast<CallInst>(Call))
|
|
if (CI->isTailCall() &&
|
|
!CI->getAttributes().hasAttrSomewhere(Attribute::ByVal))
|
|
return ModRefInfo::NoModRef;
|
|
|
|
// Stack restore is able to modify unescaped dynamic allocas. Assume it may
|
|
// modify them even though the alloca is not escaped.
|
|
if (auto *AI = dyn_cast<AllocaInst>(Object))
|
|
if (!AI->isStaticAlloca() && isIntrinsicCall(Call, Intrinsic::stackrestore))
|
|
return ModRefInfo::Mod;
|
|
|
|
// If the pointer is to a locally allocated object that does not escape,
|
|
// then the call can not mod/ref the pointer unless the call takes the pointer
|
|
// as an argument, and itself doesn't capture it.
|
|
if (!isa<Constant>(Object) && Call != Object &&
|
|
AAQI.CI->isNotCapturedBeforeOrAt(Object, Call)) {
|
|
|
|
// Optimistically assume that call doesn't touch Object and check this
|
|
// assumption in the following loop.
|
|
ModRefInfo Result = ModRefInfo::NoModRef;
|
|
bool IsMustAlias = true;
|
|
|
|
unsigned OperandNo = 0;
|
|
for (auto CI = Call->data_operands_begin(), CE = Call->data_operands_end();
|
|
CI != CE; ++CI, ++OperandNo) {
|
|
// Only look at the no-capture or byval pointer arguments. If this
|
|
// pointer were passed to arguments that were neither of these, then it
|
|
// couldn't be no-capture.
|
|
if (!(*CI)->getType()->isPointerTy() ||
|
|
(!Call->doesNotCapture(OperandNo) && OperandNo < Call->arg_size() &&
|
|
!Call->isByValArgument(OperandNo)))
|
|
continue;
|
|
|
|
// Call doesn't access memory through this operand, so we don't care
|
|
// if it aliases with Object.
|
|
if (Call->doesNotAccessMemory(OperandNo))
|
|
continue;
|
|
|
|
// If this is a no-capture pointer argument, see if we can tell that it
|
|
// is impossible to alias the pointer we're checking.
|
|
AliasResult AR = getBestAAResults().alias(
|
|
MemoryLocation::getBeforeOrAfter(*CI),
|
|
MemoryLocation::getBeforeOrAfter(Object), AAQI);
|
|
if (AR != AliasResult::MustAlias)
|
|
IsMustAlias = false;
|
|
// Operand doesn't alias 'Object', continue looking for other aliases
|
|
if (AR == AliasResult::NoAlias)
|
|
continue;
|
|
// Operand aliases 'Object', but call doesn't modify it. Strengthen
|
|
// initial assumption and keep looking in case if there are more aliases.
|
|
if (Call->onlyReadsMemory(OperandNo)) {
|
|
Result = setRef(Result);
|
|
continue;
|
|
}
|
|
// Operand aliases 'Object' but call only writes into it.
|
|
if (Call->onlyWritesMemory(OperandNo)) {
|
|
Result = setMod(Result);
|
|
continue;
|
|
}
|
|
// This operand aliases 'Object' and call reads and writes into it.
|
|
// Setting ModRef will not yield an early return below, MustAlias is not
|
|
// used further.
|
|
Result = ModRefInfo::ModRef;
|
|
break;
|
|
}
|
|
|
|
// No operand aliases, reset Must bit. Add below if at least one aliases
|
|
// and all aliases found are MustAlias.
|
|
if (isNoModRef(Result))
|
|
IsMustAlias = false;
|
|
|
|
// Early return if we improved mod ref information
|
|
if (!isModAndRefSet(Result)) {
|
|
if (isNoModRef(Result))
|
|
return ModRefInfo::NoModRef;
|
|
return IsMustAlias ? setMust(Result) : clearMust(Result);
|
|
}
|
|
}
|
|
|
|
// If the call is malloc/calloc like, we can assume that it doesn't
|
|
// modify any IR visible value. This is only valid because we assume these
|
|
// routines do not read values visible in the IR. TODO: Consider special
|
|
// casing realloc and strdup routines which access only their arguments as
|
|
// well. Or alternatively, replace all of this with inaccessiblememonly once
|
|
// that's implemented fully.
|
|
if (isMallocOrCallocLikeFn(Call, &TLI)) {
|
|
// Be conservative if the accessed pointer may alias the allocation -
|
|
// fallback to the generic handling below.
|
|
if (getBestAAResults().alias(MemoryLocation::getBeforeOrAfter(Call), Loc,
|
|
AAQI) == AliasResult::NoAlias)
|
|
return ModRefInfo::NoModRef;
|
|
}
|
|
|
|
// Ideally, there should be no need to special case for memcpy/memove
|
|
// intrinsics here since general machinery (based on memory attributes) should
|
|
// already handle it just fine. Unfortunately, it doesn't due to deficiency in
|
|
// operand bundles support. At the moment it's not clear if complexity behind
|
|
// enhancing general mechanism worths it.
|
|
// TODO: Consider improving operand bundles support in general mechanism.
|
|
if (auto *Inst = dyn_cast<AnyMemTransferInst>(Call)) {
|
|
AliasResult SrcAA =
|
|
getBestAAResults().alias(MemoryLocation::getForSource(Inst), Loc, AAQI);
|
|
AliasResult DestAA =
|
|
getBestAAResults().alias(MemoryLocation::getForDest(Inst), Loc, AAQI);
|
|
// It's also possible for Loc to alias both src and dest, or neither.
|
|
ModRefInfo rv = ModRefInfo::NoModRef;
|
|
if (SrcAA != AliasResult::NoAlias || Call->hasReadingOperandBundles())
|
|
rv = setRef(rv);
|
|
if (DestAA != AliasResult::NoAlias || Call->hasClobberingOperandBundles())
|
|
rv = setMod(rv);
|
|
return rv;
|
|
}
|
|
|
|
// Guard intrinsics are marked as arbitrarily writing so that proper control
|
|
// dependencies are maintained but they never mods any particular memory
|
|
// location.
|
|
//
|
|
// *Unlike* assumes, guard intrinsics are modeled as reading memory since the
|
|
// heap state at the point the guard is issued needs to be consistent in case
|
|
// the guard invokes the "deopt" continuation.
|
|
if (isIntrinsicCall(Call, Intrinsic::experimental_guard))
|
|
return ModRefInfo::Ref;
|
|
// The same applies to deoptimize which is essentially a guard(false).
|
|
if (isIntrinsicCall(Call, Intrinsic::experimental_deoptimize))
|
|
return ModRefInfo::Ref;
|
|
|
|
// Like assumes, invariant.start intrinsics were also marked as arbitrarily
|
|
// writing so that proper control dependencies are maintained but they never
|
|
// mod any particular memory location visible to the IR.
|
|
// *Unlike* assumes (which are now modeled as NoModRef), invariant.start
|
|
// intrinsic is now modeled as reading memory. This prevents hoisting the
|
|
// invariant.start intrinsic over stores. Consider:
|
|
// *ptr = 40;
|
|
// *ptr = 50;
|
|
// invariant_start(ptr)
|
|
// int val = *ptr;
|
|
// print(val);
|
|
//
|
|
// This cannot be transformed to:
|
|
//
|
|
// *ptr = 40;
|
|
// invariant_start(ptr)
|
|
// *ptr = 50;
|
|
// int val = *ptr;
|
|
// print(val);
|
|
//
|
|
// The transformation will cause the second store to be ignored (based on
|
|
// rules of invariant.start) and print 40, while the first program always
|
|
// prints 50.
|
|
if (isIntrinsicCall(Call, Intrinsic::invariant_start))
|
|
return ModRefInfo::Ref;
|
|
|
|
// The AAResultBase base class has some smarts, lets use them.
|
|
return AAResultBase::getModRefInfo(Call, Loc, AAQI);
|
|
}
|
|
|
|
ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call1,
|
|
const CallBase *Call2,
|
|
AAQueryInfo &AAQI) {
|
|
// Guard intrinsics are marked as arbitrarily writing so that proper control
|
|
// dependencies are maintained but they never mods any particular memory
|
|
// location.
|
|
//
|
|
// *Unlike* assumes, guard intrinsics are modeled as reading memory since the
|
|
// heap state at the point the guard is issued needs to be consistent in case
|
|
// the guard invokes the "deopt" continuation.
|
|
|
|
// NB! This function is *not* commutative, so we special case two
|
|
// possibilities for guard intrinsics.
|
|
|
|
if (isIntrinsicCall(Call1, Intrinsic::experimental_guard))
|
|
return isModSet(createModRefInfo(getModRefBehavior(Call2)))
|
|
? ModRefInfo::Ref
|
|
: ModRefInfo::NoModRef;
|
|
|
|
if (isIntrinsicCall(Call2, Intrinsic::experimental_guard))
|
|
return isModSet(createModRefInfo(getModRefBehavior(Call1)))
|
|
? ModRefInfo::Mod
|
|
: ModRefInfo::NoModRef;
|
|
|
|
// The AAResultBase base class has some smarts, lets use them.
|
|
return AAResultBase::getModRefInfo(Call1, Call2, AAQI);
|
|
}
|
|
|
|
/// Return true if we know V to the base address of the corresponding memory
|
|
/// object. This implies that any address less than V must be out of bounds
|
|
/// for the underlying object. Note that just being isIdentifiedObject() is
|
|
/// not enough - For example, a negative offset from a noalias argument or call
|
|
/// can be inbounds w.r.t the actual underlying object.
|
|
static bool isBaseOfObject(const Value *V) {
|
|
// TODO: We can handle other cases here
|
|
// 1) For GC languages, arguments to functions are often required to be
|
|
// base pointers.
|
|
// 2) Result of allocation routines are often base pointers. Leverage TLI.
|
|
return (isa<AllocaInst>(V) || isa<GlobalVariable>(V));
|
|
}
|
|
|
|
/// Provides a bunch of ad-hoc rules to disambiguate a GEP instruction against
|
|
/// another pointer.
|
|
///
|
|
/// We know that V1 is a GEP, but we don't know anything about V2.
|
|
/// UnderlyingV1 is getUnderlyingObject(GEP1), UnderlyingV2 is the same for
|
|
/// V2.
|
|
AliasResult BasicAAResult::aliasGEP(
|
|
const GEPOperator *GEP1, LocationSize V1Size,
|
|
const Value *V2, LocationSize V2Size,
|
|
const Value *UnderlyingV1, const Value *UnderlyingV2, AAQueryInfo &AAQI) {
|
|
if (!V1Size.hasValue() && !V2Size.hasValue()) {
|
|
// TODO: This limitation exists for compile-time reasons. Relax it if we
|
|
// can avoid exponential pathological cases.
|
|
if (!isa<GEPOperator>(V2))
|
|
return AliasResult::MayAlias;
|
|
|
|
// If both accesses have unknown size, we can only check whether the base
|
|
// objects don't alias.
|
|
AliasResult BaseAlias = getBestAAResults().alias(
|
|
MemoryLocation::getBeforeOrAfter(UnderlyingV1),
|
|
MemoryLocation::getBeforeOrAfter(UnderlyingV2), AAQI);
|
|
return BaseAlias == AliasResult::NoAlias ? AliasResult::NoAlias
|
|
: AliasResult::MayAlias;
|
|
}
|
|
|
|
DecomposedGEP DecompGEP1 = DecomposeGEPExpression(GEP1, DL, &AC, DT);
|
|
DecomposedGEP DecompGEP2 = DecomposeGEPExpression(V2, DL, &AC, DT);
|
|
|
|
// Bail if we were not able to decompose anything.
|
|
if (DecompGEP1.Base == GEP1 && DecompGEP2.Base == V2)
|
|
return AliasResult::MayAlias;
|
|
|
|
// Subtract the GEP2 pointer from the GEP1 pointer to find out their
|
|
// symbolic difference.
|
|
subtractDecomposedGEPs(DecompGEP1, DecompGEP2);
|
|
|
|
// If an inbounds GEP would have to start from an out of bounds address
|
|
// for the two to alias, then we can assume noalias.
|
|
if (*DecompGEP1.InBounds && DecompGEP1.VarIndices.empty() &&
|
|
V2Size.hasValue() && DecompGEP1.Offset.sge(V2Size.getValue()) &&
|
|
isBaseOfObject(DecompGEP2.Base))
|
|
return AliasResult::NoAlias;
|
|
|
|
if (isa<GEPOperator>(V2)) {
|
|
// Symmetric case to above.
|
|
if (*DecompGEP2.InBounds && DecompGEP1.VarIndices.empty() &&
|
|
V1Size.hasValue() && DecompGEP1.Offset.sle(-V1Size.getValue()) &&
|
|
isBaseOfObject(DecompGEP1.Base))
|
|
return AliasResult::NoAlias;
|
|
}
|
|
|
|
// For GEPs with identical offsets, we can preserve the size and AAInfo
|
|
// when performing the alias check on the underlying objects.
|
|
if (DecompGEP1.Offset == 0 && DecompGEP1.VarIndices.empty())
|
|
return getBestAAResults().alias(MemoryLocation(DecompGEP1.Base, V1Size),
|
|
MemoryLocation(DecompGEP2.Base, V2Size),
|
|
AAQI);
|
|
|
|
// Do the base pointers alias?
|
|
AliasResult BaseAlias = getBestAAResults().alias(
|
|
MemoryLocation::getBeforeOrAfter(DecompGEP1.Base),
|
|
MemoryLocation::getBeforeOrAfter(DecompGEP2.Base), AAQI);
|
|
|
|
// If we get a No or May, then return it immediately, no amount of analysis
|
|
// will improve this situation.
|
|
if (BaseAlias != AliasResult::MustAlias) {
|
|
assert(BaseAlias == AliasResult::NoAlias ||
|
|
BaseAlias == AliasResult::MayAlias);
|
|
return BaseAlias;
|
|
}
|
|
|
|
// If there is a constant difference between the pointers, but the difference
|
|
// is less than the size of the associated memory object, then we know
|
|
// that the objects are partially overlapping. If the difference is
|
|
// greater, we know they do not overlap.
|
|
if (DecompGEP1.VarIndices.empty()) {
|
|
APInt &Off = DecompGEP1.Offset;
|
|
|
|
// Initialize for Off >= 0 (V2 <= GEP1) case.
|
|
const Value *LeftPtr = V2;
|
|
const Value *RightPtr = GEP1;
|
|
LocationSize VLeftSize = V2Size;
|
|
LocationSize VRightSize = V1Size;
|
|
const bool Swapped = Off.isNegative();
|
|
|
|
if (Swapped) {
|
|
// Swap if we have the situation where:
|
|
// + +
|
|
// | BaseOffset |
|
|
// ---------------->|
|
|
// |-->V1Size |-------> V2Size
|
|
// GEP1 V2
|
|
std::swap(LeftPtr, RightPtr);
|
|
std::swap(VLeftSize, VRightSize);
|
|
Off = -Off;
|
|
}
|
|
|
|
if (!VLeftSize.hasValue())
|
|
return AliasResult::MayAlias;
|
|
|
|
const uint64_t LSize = VLeftSize.getValue();
|
|
if (Off.ult(LSize)) {
|
|
// Conservatively drop processing if a phi was visited and/or offset is
|
|
// too big.
|
|
AliasResult AR = AliasResult::PartialAlias;
|
|
if (VRightSize.hasValue() && Off.ule(INT32_MAX) &&
|
|
(Off + VRightSize.getValue()).ule(LSize)) {
|
|
// Memory referenced by right pointer is nested. Save the offset in
|
|
// cache. Note that originally offset estimated as GEP1-V2, but
|
|
// AliasResult contains the shift that represents GEP1+Offset=V2.
|
|
AR.setOffset(-Off.getSExtValue());
|
|
AR.swap(Swapped);
|
|
}
|
|
return AR;
|
|
}
|
|
return AliasResult::NoAlias;
|
|
}
|
|
|
|
// We need to know both acess sizes for all the following heuristics.
|
|
if (!V1Size.hasValue() || !V2Size.hasValue())
|
|
return AliasResult::MayAlias;
|
|
|
|
APInt GCD;
|
|
ConstantRange OffsetRange = ConstantRange(DecompGEP1.Offset);
|
|
for (unsigned i = 0, e = DecompGEP1.VarIndices.size(); i != e; ++i) {
|
|
const VariableGEPIndex &Index = DecompGEP1.VarIndices[i];
|
|
const APInt &Scale = Index.Scale;
|
|
APInt ScaleForGCD = Scale;
|
|
if (!Index.IsNSW)
|
|
ScaleForGCD = APInt::getOneBitSet(Scale.getBitWidth(),
|
|
Scale.countTrailingZeros());
|
|
|
|
if (i == 0)
|
|
GCD = ScaleForGCD.abs();
|
|
else
|
|
GCD = APIntOps::GreatestCommonDivisor(GCD, ScaleForGCD.abs());
|
|
|
|
ConstantRange CR = computeConstantRange(Index.Val.V, /* ForSigned */ false,
|
|
true, &AC, Index.CxtI);
|
|
KnownBits Known =
|
|
computeKnownBits(Index.Val.V, DL, 0, &AC, Index.CxtI, DT);
|
|
CR = CR.intersectWith(
|
|
ConstantRange::fromKnownBits(Known, /* Signed */ true),
|
|
ConstantRange::Signed);
|
|
CR = Index.Val.evaluateWith(CR).sextOrTrunc(OffsetRange.getBitWidth());
|
|
|
|
assert(OffsetRange.getBitWidth() == Scale.getBitWidth() &&
|
|
"Bit widths are normalized to MaxIndexSize");
|
|
if (Index.IsNSW)
|
|
OffsetRange = OffsetRange.add(CR.smul_sat(ConstantRange(Scale)));
|
|
else
|
|
OffsetRange = OffsetRange.add(CR.smul_fast(ConstantRange(Scale)));
|
|
}
|
|
|
|
// We now have accesses at two offsets from the same base:
|
|
// 1. (...)*GCD + DecompGEP1.Offset with size V1Size
|
|
// 2. 0 with size V2Size
|
|
// Using arithmetic modulo GCD, the accesses are at
|
|
// [ModOffset..ModOffset+V1Size) and [0..V2Size). If the first access fits
|
|
// into the range [V2Size..GCD), then we know they cannot overlap.
|
|
APInt ModOffset = DecompGEP1.Offset.srem(GCD);
|
|
if (ModOffset.isNegative())
|
|
ModOffset += GCD; // We want mod, not rem.
|
|
if (ModOffset.uge(V2Size.getValue()) &&
|
|
(GCD - ModOffset).uge(V1Size.getValue()))
|
|
return AliasResult::NoAlias;
|
|
|
|
// Compute ranges of potentially accessed bytes for both accesses. If the
|
|
// interseciton is empty, there can be no overlap.
|
|
unsigned BW = OffsetRange.getBitWidth();
|
|
ConstantRange Range1 = OffsetRange.add(
|
|
ConstantRange(APInt(BW, 0), APInt(BW, V1Size.getValue())));
|
|
ConstantRange Range2 =
|
|
ConstantRange(APInt(BW, 0), APInt(BW, V2Size.getValue()));
|
|
if (Range1.intersectWith(Range2).isEmptySet())
|
|
return AliasResult::NoAlias;
|
|
|
|
// Try to determine the range of values for VarIndex such that
|
|
// VarIndex <= -MinAbsVarIndex || MinAbsVarIndex <= VarIndex.
|
|
Optional<APInt> MinAbsVarIndex;
|
|
if (DecompGEP1.VarIndices.size() == 1) {
|
|
// VarIndex = Scale*V.
|
|
const VariableGEPIndex &Var = DecompGEP1.VarIndices[0];
|
|
if (Var.Val.TruncBits == 0 &&
|
|
isKnownNonZero(Var.Val.V, DL, 0, &AC, Var.CxtI, DT)) {
|
|
// If V != 0, then abs(VarIndex) > 0.
|
|
MinAbsVarIndex = APInt(Var.Scale.getBitWidth(), 1);
|
|
|
|
// Check if abs(V*Scale) >= abs(Scale) holds in the presence of
|
|
// potentially wrapping math.
|
|
auto MultiplyByScaleNoWrap = [](const VariableGEPIndex &Var) {
|
|
if (Var.IsNSW)
|
|
return true;
|
|
|
|
int ValOrigBW = Var.Val.V->getType()->getPrimitiveSizeInBits();
|
|
// If Scale is small enough so that abs(V*Scale) >= abs(Scale) holds.
|
|
// The max value of abs(V) is 2^ValOrigBW - 1. Multiplying with a
|
|
// constant smaller than 2^(bitwidth(Val) - ValOrigBW) won't wrap.
|
|
int MaxScaleValueBW = Var.Val.getBitWidth() - ValOrigBW;
|
|
if (MaxScaleValueBW <= 0)
|
|
return false;
|
|
return Var.Scale.ule(
|
|
APInt::getMaxValue(MaxScaleValueBW).zext(Var.Scale.getBitWidth()));
|
|
};
|
|
// Refine MinAbsVarIndex, if abs(Scale*V) >= abs(Scale) holds in the
|
|
// presence of potentially wrapping math.
|
|
if (MultiplyByScaleNoWrap(Var)) {
|
|
// If V != 0 then abs(VarIndex) >= abs(Scale).
|
|
MinAbsVarIndex = Var.Scale.abs();
|
|
}
|
|
}
|
|
} else if (DecompGEP1.VarIndices.size() == 2) {
|
|
// VarIndex = Scale*V0 + (-Scale)*V1.
|
|
// If V0 != V1 then abs(VarIndex) >= abs(Scale).
|
|
// Check that VisitedPhiBBs is empty, to avoid reasoning about
|
|
// inequality of values across loop iterations.
|
|
const VariableGEPIndex &Var0 = DecompGEP1.VarIndices[0];
|
|
const VariableGEPIndex &Var1 = DecompGEP1.VarIndices[1];
|
|
if (Var0.Scale == -Var1.Scale && Var0.Val.TruncBits == 0 &&
|
|
Var0.Val.hasSameCastsAs(Var1.Val) && VisitedPhiBBs.empty() &&
|
|
isKnownNonEqual(Var0.Val.V, Var1.Val.V, DL, &AC, /* CxtI */ nullptr,
|
|
DT))
|
|
MinAbsVarIndex = Var0.Scale.abs();
|
|
}
|
|
|
|
if (MinAbsVarIndex) {
|
|
// The constant offset will have added at least +/-MinAbsVarIndex to it.
|
|
APInt OffsetLo = DecompGEP1.Offset - *MinAbsVarIndex;
|
|
APInt OffsetHi = DecompGEP1.Offset + *MinAbsVarIndex;
|
|
// We know that Offset <= OffsetLo || Offset >= OffsetHi
|
|
if (OffsetLo.isNegative() && (-OffsetLo).uge(V1Size.getValue()) &&
|
|
OffsetHi.isNonNegative() && OffsetHi.uge(V2Size.getValue()))
|
|
return AliasResult::NoAlias;
|
|
}
|
|
|
|
if (constantOffsetHeuristic(DecompGEP1, V1Size, V2Size, &AC, DT))
|
|
return AliasResult::NoAlias;
|
|
|
|
// Statically, we can see that the base objects are the same, but the
|
|
// pointers have dynamic offsets which we can't resolve. And none of our
|
|
// little tricks above worked.
|
|
return AliasResult::MayAlias;
|
|
}
|
|
|
|
static AliasResult MergeAliasResults(AliasResult A, AliasResult B) {
|
|
// If the results agree, take it.
|
|
if (A == B)
|
|
return A;
|
|
// A mix of PartialAlias and MustAlias is PartialAlias.
|
|
if ((A == AliasResult::PartialAlias && B == AliasResult::MustAlias) ||
|
|
(B == AliasResult::PartialAlias && A == AliasResult::MustAlias))
|
|
return AliasResult::PartialAlias;
|
|
// Otherwise, we don't know anything.
|
|
return AliasResult::MayAlias;
|
|
}
|
|
|
|
/// Provides a bunch of ad-hoc rules to disambiguate a Select instruction
|
|
/// against another.
|
|
AliasResult
|
|
BasicAAResult::aliasSelect(const SelectInst *SI, LocationSize SISize,
|
|
const Value *V2, LocationSize V2Size,
|
|
AAQueryInfo &AAQI) {
|
|
// If the values are Selects with the same condition, we can do a more precise
|
|
// check: just check for aliases between the values on corresponding arms.
|
|
if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
|
|
if (SI->getCondition() == SI2->getCondition()) {
|
|
AliasResult Alias = getBestAAResults().alias(
|
|
MemoryLocation(SI->getTrueValue(), SISize),
|
|
MemoryLocation(SI2->getTrueValue(), V2Size), AAQI);
|
|
if (Alias == AliasResult::MayAlias)
|
|
return AliasResult::MayAlias;
|
|
AliasResult ThisAlias = getBestAAResults().alias(
|
|
MemoryLocation(SI->getFalseValue(), SISize),
|
|
MemoryLocation(SI2->getFalseValue(), V2Size), AAQI);
|
|
return MergeAliasResults(ThisAlias, Alias);
|
|
}
|
|
|
|
// If both arms of the Select node NoAlias or MustAlias V2, then returns
|
|
// NoAlias / MustAlias. Otherwise, returns MayAlias.
|
|
AliasResult Alias =
|
|
getBestAAResults().alias(MemoryLocation(SI->getTrueValue(), SISize),
|
|
MemoryLocation(V2, V2Size), AAQI);
|
|
if (Alias == AliasResult::MayAlias)
|
|
return AliasResult::MayAlias;
|
|
|
|
AliasResult ThisAlias =
|
|
getBestAAResults().alias(MemoryLocation(SI->getFalseValue(), SISize),
|
|
MemoryLocation(V2, V2Size), AAQI);
|
|
return MergeAliasResults(ThisAlias, Alias);
|
|
}
|
|
|
|
/// Provide a bunch of ad-hoc rules to disambiguate a PHI instruction against
|
|
/// another.
|
|
AliasResult BasicAAResult::aliasPHI(const PHINode *PN, LocationSize PNSize,
|
|
const Value *V2, LocationSize V2Size,
|
|
AAQueryInfo &AAQI) {
|
|
if (!PN->getNumIncomingValues())
|
|
return AliasResult::NoAlias;
|
|
// If the values are PHIs in the same block, we can do a more precise
|
|
// as well as efficient check: just check for aliases between the values
|
|
// on corresponding edges.
|
|
if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
|
|
if (PN2->getParent() == PN->getParent()) {
|
|
Optional<AliasResult> Alias;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
AliasResult ThisAlias = getBestAAResults().alias(
|
|
MemoryLocation(PN->getIncomingValue(i), PNSize),
|
|
MemoryLocation(
|
|
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), V2Size),
|
|
AAQI);
|
|
if (Alias)
|
|
*Alias = MergeAliasResults(*Alias, ThisAlias);
|
|
else
|
|
Alias = ThisAlias;
|
|
if (*Alias == AliasResult::MayAlias)
|
|
break;
|
|
}
|
|
return *Alias;
|
|
}
|
|
|
|
SmallVector<Value *, 4> V1Srcs;
|
|
// If a phi operand recurses back to the phi, we can still determine NoAlias
|
|
// if we don't alias the underlying objects of the other phi operands, as we
|
|
// know that the recursive phi needs to be based on them in some way.
|
|
bool isRecursive = false;
|
|
auto CheckForRecPhi = [&](Value *PV) {
|
|
if (!EnableRecPhiAnalysis)
|
|
return false;
|
|
if (getUnderlyingObject(PV) == PN) {
|
|
isRecursive = true;
|
|
return true;
|
|
}
|
|
return false;
|
|
};
|
|
|
|
if (PV) {
|
|
// If we have PhiValues then use it to get the underlying phi values.
|
|
const PhiValues::ValueSet &PhiValueSet = PV->getValuesForPhi(PN);
|
|
// If we have more phi values than the search depth then return MayAlias
|
|
// conservatively to avoid compile time explosion. The worst possible case
|
|
// is if both sides are PHI nodes. In which case, this is O(m x n) time
|
|
// where 'm' and 'n' are the number of PHI sources.
|
|
if (PhiValueSet.size() > MaxLookupSearchDepth)
|
|
return AliasResult::MayAlias;
|
|
// Add the values to V1Srcs
|
|
for (Value *PV1 : PhiValueSet) {
|
|
if (CheckForRecPhi(PV1))
|
|
continue;
|
|
V1Srcs.push_back(PV1);
|
|
}
|
|
} else {
|
|
// If we don't have PhiInfo then just look at the operands of the phi itself
|
|
// FIXME: Remove this once we can guarantee that we have PhiInfo always
|
|
SmallPtrSet<Value *, 4> UniqueSrc;
|
|
Value *OnePhi = nullptr;
|
|
for (Value *PV1 : PN->incoming_values()) {
|
|
if (isa<PHINode>(PV1)) {
|
|
if (OnePhi && OnePhi != PV1) {
|
|
// To control potential compile time explosion, we choose to be
|
|
// conserviate when we have more than one Phi input. It is important
|
|
// that we handle the single phi case as that lets us handle LCSSA
|
|
// phi nodes and (combined with the recursive phi handling) simple
|
|
// pointer induction variable patterns.
|
|
return AliasResult::MayAlias;
|
|
}
|
|
OnePhi = PV1;
|
|
}
|
|
|
|
if (CheckForRecPhi(PV1))
|
|
continue;
|
|
|
|
if (UniqueSrc.insert(PV1).second)
|
|
V1Srcs.push_back(PV1);
|
|
}
|
|
|
|
if (OnePhi && UniqueSrc.size() > 1)
|
|
// Out of an abundance of caution, allow only the trivial lcssa and
|
|
// recursive phi cases.
|
|
return AliasResult::MayAlias;
|
|
}
|
|
|
|
// If V1Srcs is empty then that means that the phi has no underlying non-phi
|
|
// value. This should only be possible in blocks unreachable from the entry
|
|
// block, but return MayAlias just in case.
|
|
if (V1Srcs.empty())
|
|
return AliasResult::MayAlias;
|
|
|
|
// If this PHI node is recursive, indicate that the pointer may be moved
|
|
// across iterations. We can only prove NoAlias if different underlying
|
|
// objects are involved.
|
|
if (isRecursive)
|
|
PNSize = LocationSize::beforeOrAfterPointer();
|
|
|
|
// In the recursive alias queries below, we may compare values from two
|
|
// different loop iterations. Keep track of visited phi blocks, which will
|
|
// be used when determining value equivalence.
|
|
bool BlockInserted = VisitedPhiBBs.insert(PN->getParent()).second;
|
|
auto _ = make_scope_exit([&]() {
|
|
if (BlockInserted)
|
|
VisitedPhiBBs.erase(PN->getParent());
|
|
});
|
|
|
|
// If we inserted a block into VisitedPhiBBs, alias analysis results that
|
|
// have been cached earlier may no longer be valid. Perform recursive queries
|
|
// with a new AAQueryInfo.
|
|
AAQueryInfo NewAAQI = AAQI.withEmptyCache();
|
|
AAQueryInfo *UseAAQI = BlockInserted ? &NewAAQI : &AAQI;
|
|
|
|
AliasResult Alias = getBestAAResults().alias(
|
|
MemoryLocation(V1Srcs[0], PNSize), MemoryLocation(V2, V2Size), *UseAAQI);
|
|
|
|
// Early exit if the check of the first PHI source against V2 is MayAlias.
|
|
// Other results are not possible.
|
|
if (Alias == AliasResult::MayAlias)
|
|
return AliasResult::MayAlias;
|
|
// With recursive phis we cannot guarantee that MustAlias/PartialAlias will
|
|
// remain valid to all elements and needs to conservatively return MayAlias.
|
|
if (isRecursive && Alias != AliasResult::NoAlias)
|
|
return AliasResult::MayAlias;
|
|
|
|
// If all sources of the PHI node NoAlias or MustAlias V2, then returns
|
|
// NoAlias / MustAlias. Otherwise, returns MayAlias.
|
|
for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
|
|
Value *V = V1Srcs[i];
|
|
|
|
AliasResult ThisAlias = getBestAAResults().alias(
|
|
MemoryLocation(V, PNSize), MemoryLocation(V2, V2Size), *UseAAQI);
|
|
Alias = MergeAliasResults(ThisAlias, Alias);
|
|
if (Alias == AliasResult::MayAlias)
|
|
break;
|
|
}
|
|
|
|
return Alias;
|
|
}
|
|
|
|
/// Provides a bunch of ad-hoc rules to disambiguate in common cases, such as
|
|
/// array references.
|
|
AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size,
|
|
const Value *V2, LocationSize V2Size,
|
|
AAQueryInfo &AAQI) {
|
|
// If either of the memory references is empty, it doesn't matter what the
|
|
// pointer values are.
|
|
if (V1Size.isZero() || V2Size.isZero())
|
|
return AliasResult::NoAlias;
|
|
|
|
// Strip off any casts if they exist.
|
|
V1 = V1->stripPointerCastsForAliasAnalysis();
|
|
V2 = V2->stripPointerCastsForAliasAnalysis();
|
|
|
|
// If V1 or V2 is undef, the result is NoAlias because we can always pick a
|
|
// value for undef that aliases nothing in the program.
|
|
if (isa<UndefValue>(V1) || isa<UndefValue>(V2))
|
|
return AliasResult::NoAlias;
|
|
|
|
// Are we checking for alias of the same value?
|
|
// Because we look 'through' phi nodes, we could look at "Value" pointers from
|
|
// different iterations. We must therefore make sure that this is not the
|
|
// case. The function isValueEqualInPotentialCycles ensures that this cannot
|
|
// happen by looking at the visited phi nodes and making sure they cannot
|
|
// reach the value.
|
|
if (isValueEqualInPotentialCycles(V1, V2))
|
|
return AliasResult::MustAlias;
|
|
|
|
if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
|
|
return AliasResult::NoAlias; // Scalars cannot alias each other
|
|
|
|
// Figure out what objects these things are pointing to if we can.
|
|
const Value *O1 = getUnderlyingObject(V1, MaxLookupSearchDepth);
|
|
const Value *O2 = getUnderlyingObject(V2, MaxLookupSearchDepth);
|
|
|
|
// Null values in the default address space don't point to any object, so they
|
|
// don't alias any other pointer.
|
|
if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
|
|
if (!NullPointerIsDefined(&F, CPN->getType()->getAddressSpace()))
|
|
return AliasResult::NoAlias;
|
|
if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
|
|
if (!NullPointerIsDefined(&F, CPN->getType()->getAddressSpace()))
|
|
return AliasResult::NoAlias;
|
|
|
|
if (O1 != O2) {
|
|
// If V1/V2 point to two different objects, we know that we have no alias.
|
|
if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
|
|
return AliasResult::NoAlias;
|
|
|
|
// Constant pointers can't alias with non-const isIdentifiedObject objects.
|
|
if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
|
|
(isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
|
|
return AliasResult::NoAlias;
|
|
|
|
// Function arguments can't alias with things that are known to be
|
|
// unambigously identified at the function level.
|
|
if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
|
|
(isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
|
|
return AliasResult::NoAlias;
|
|
|
|
// If one pointer is the result of a call/invoke or load and the other is a
|
|
// non-escaping local object within the same function, then we know the
|
|
// object couldn't escape to a point where the call could return it.
|
|
//
|
|
// Note that if the pointers are in different functions, there are a
|
|
// variety of complications. A call with a nocapture argument may still
|
|
// temporary store the nocapture argument's value in a temporary memory
|
|
// location if that memory location doesn't escape. Or it may pass a
|
|
// nocapture value to other functions as long as they don't capture it.
|
|
if (isEscapeSource(O1) &&
|
|
AAQI.CI->isNotCapturedBeforeOrAt(O2, cast<Instruction>(O1)))
|
|
return AliasResult::NoAlias;
|
|
if (isEscapeSource(O2) &&
|
|
AAQI.CI->isNotCapturedBeforeOrAt(O1, cast<Instruction>(O2)))
|
|
return AliasResult::NoAlias;
|
|
}
|
|
|
|
// If the size of one access is larger than the entire object on the other
|
|
// side, then we know such behavior is undefined and can assume no alias.
|
|
bool NullIsValidLocation = NullPointerIsDefined(&F);
|
|
if ((isObjectSmallerThan(
|
|
O2, getMinimalExtentFrom(*V1, V1Size, DL, NullIsValidLocation), DL,
|
|
TLI, NullIsValidLocation)) ||
|
|
(isObjectSmallerThan(
|
|
O1, getMinimalExtentFrom(*V2, V2Size, DL, NullIsValidLocation), DL,
|
|
TLI, NullIsValidLocation)))
|
|
return AliasResult::NoAlias;
|
|
|
|
// If one the accesses may be before the accessed pointer, canonicalize this
|
|
// by using unknown after-pointer sizes for both accesses. This is
|
|
// equivalent, because regardless of which pointer is lower, one of them
|
|
// will always came after the other, as long as the underlying objects aren't
|
|
// disjoint. We do this so that the rest of BasicAA does not have to deal
|
|
// with accesses before the base pointer, and to improve cache utilization by
|
|
// merging equivalent states.
|
|
if (V1Size.mayBeBeforePointer() || V2Size.mayBeBeforePointer()) {
|
|
V1Size = LocationSize::afterPointer();
|
|
V2Size = LocationSize::afterPointer();
|
|
}
|
|
|
|
// FIXME: If this depth limit is hit, then we may cache sub-optimal results
|
|
// for recursive queries. For this reason, this limit is chosen to be large
|
|
// enough to be very rarely hit, while still being small enough to avoid
|
|
// stack overflows.
|
|
if (AAQI.Depth >= 512)
|
|
return AliasResult::MayAlias;
|
|
|
|
// Check the cache before climbing up use-def chains. This also terminates
|
|
// otherwise infinitely recursive queries.
|
|
AAQueryInfo::LocPair Locs({V1, V1Size}, {V2, V2Size});
|
|
const bool Swapped = V1 > V2;
|
|
if (Swapped)
|
|
std::swap(Locs.first, Locs.second);
|
|
const auto &Pair = AAQI.AliasCache.try_emplace(
|
|
Locs, AAQueryInfo::CacheEntry{AliasResult::NoAlias, 0});
|
|
if (!Pair.second) {
|
|
auto &Entry = Pair.first->second;
|
|
if (!Entry.isDefinitive()) {
|
|
// Remember that we used an assumption.
|
|
++Entry.NumAssumptionUses;
|
|
++AAQI.NumAssumptionUses;
|
|
}
|
|
// Cache contains sorted {V1,V2} pairs but we should return original order.
|
|
auto Result = Entry.Result;
|
|
Result.swap(Swapped);
|
|
return Result;
|
|
}
|
|
|
|
int OrigNumAssumptionUses = AAQI.NumAssumptionUses;
|
|
unsigned OrigNumAssumptionBasedResults = AAQI.AssumptionBasedResults.size();
|
|
AliasResult Result =
|
|
aliasCheckRecursive(V1, V1Size, V2, V2Size, AAQI, O1, O2);
|
|
|
|
auto It = AAQI.AliasCache.find(Locs);
|
|
assert(It != AAQI.AliasCache.end() && "Must be in cache");
|
|
auto &Entry = It->second;
|
|
|
|
// Check whether a NoAlias assumption has been used, but disproven.
|
|
bool AssumptionDisproven =
|
|
Entry.NumAssumptionUses > 0 && Result != AliasResult::NoAlias;
|
|
if (AssumptionDisproven)
|
|
Result = AliasResult::MayAlias;
|
|
|
|
// This is a definitive result now, when considered as a root query.
|
|
AAQI.NumAssumptionUses -= Entry.NumAssumptionUses;
|
|
Entry.Result = Result;
|
|
// Cache contains sorted {V1,V2} pairs.
|
|
Entry.Result.swap(Swapped);
|
|
Entry.NumAssumptionUses = -1;
|
|
|
|
// If the assumption has been disproven, remove any results that may have
|
|
// been based on this assumption. Do this after the Entry updates above to
|
|
// avoid iterator invalidation.
|
|
if (AssumptionDisproven)
|
|
while (AAQI.AssumptionBasedResults.size() > OrigNumAssumptionBasedResults)
|
|
AAQI.AliasCache.erase(AAQI.AssumptionBasedResults.pop_back_val());
|
|
|
|
// The result may still be based on assumptions higher up in the chain.
|
|
// Remember it, so it can be purged from the cache later.
|
|
if (OrigNumAssumptionUses != AAQI.NumAssumptionUses &&
|
|
Result != AliasResult::MayAlias)
|
|
AAQI.AssumptionBasedResults.push_back(Locs);
|
|
return Result;
|
|
}
|
|
|
|
AliasResult BasicAAResult::aliasCheckRecursive(
|
|
const Value *V1, LocationSize V1Size,
|
|
const Value *V2, LocationSize V2Size,
|
|
AAQueryInfo &AAQI, const Value *O1, const Value *O2) {
|
|
if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
|
|
AliasResult Result = aliasGEP(GV1, V1Size, V2, V2Size, O1, O2, AAQI);
|
|
if (Result != AliasResult::MayAlias)
|
|
return Result;
|
|
} else if (const GEPOperator *GV2 = dyn_cast<GEPOperator>(V2)) {
|
|
AliasResult Result = aliasGEP(GV2, V2Size, V1, V1Size, O2, O1, AAQI);
|
|
Result.swap();
|
|
if (Result != AliasResult::MayAlias)
|
|
return Result;
|
|
}
|
|
|
|
if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
|
|
AliasResult Result = aliasPHI(PN, V1Size, V2, V2Size, AAQI);
|
|
if (Result != AliasResult::MayAlias)
|
|
return Result;
|
|
} else if (const PHINode *PN = dyn_cast<PHINode>(V2)) {
|
|
AliasResult Result = aliasPHI(PN, V2Size, V1, V1Size, AAQI);
|
|
Result.swap();
|
|
if (Result != AliasResult::MayAlias)
|
|
return Result;
|
|
}
|
|
|
|
if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
|
|
AliasResult Result = aliasSelect(S1, V1Size, V2, V2Size, AAQI);
|
|
if (Result != AliasResult::MayAlias)
|
|
return Result;
|
|
} else if (const SelectInst *S2 = dyn_cast<SelectInst>(V2)) {
|
|
AliasResult Result = aliasSelect(S2, V2Size, V1, V1Size, AAQI);
|
|
Result.swap();
|
|
if (Result != AliasResult::MayAlias)
|
|
return Result;
|
|
}
|
|
|
|
// If both pointers are pointing into the same object and one of them
|
|
// accesses the entire object, then the accesses must overlap in some way.
|
|
if (O1 == O2) {
|
|
bool NullIsValidLocation = NullPointerIsDefined(&F);
|
|
if (V1Size.isPrecise() && V2Size.isPrecise() &&
|
|
(isObjectSize(O1, V1Size.getValue(), DL, TLI, NullIsValidLocation) ||
|
|
isObjectSize(O2, V2Size.getValue(), DL, TLI, NullIsValidLocation)))
|
|
return AliasResult::PartialAlias;
|
|
}
|
|
|
|
return AliasResult::MayAlias;
|
|
}
|
|
|
|
/// Check whether two Values can be considered equivalent.
|
|
///
|
|
/// In addition to pointer equivalence of \p V1 and \p V2 this checks whether
|
|
/// they can not be part of a cycle in the value graph by looking at all
|
|
/// visited phi nodes an making sure that the phis cannot reach the value. We
|
|
/// have to do this because we are looking through phi nodes (That is we say
|
|
/// noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB).
|
|
bool BasicAAResult::isValueEqualInPotentialCycles(const Value *V,
|
|
const Value *V2) {
|
|
if (V != V2)
|
|
return false;
|
|
|
|
const Instruction *Inst = dyn_cast<Instruction>(V);
|
|
if (!Inst)
|
|
return true;
|
|
|
|
if (VisitedPhiBBs.empty())
|
|
return true;
|
|
|
|
if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck)
|
|
return false;
|
|
|
|
// Make sure that the visited phis cannot reach the Value. This ensures that
|
|
// the Values cannot come from different iterations of a potential cycle the
|
|
// phi nodes could be involved in.
|
|
for (auto *P : VisitedPhiBBs)
|
|
if (isPotentiallyReachable(&P->front(), Inst, nullptr, DT))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
/// Computes the symbolic difference between two de-composed GEPs.
|
|
void BasicAAResult::subtractDecomposedGEPs(DecomposedGEP &DestGEP,
|
|
const DecomposedGEP &SrcGEP) {
|
|
DestGEP.Offset -= SrcGEP.Offset;
|
|
for (const VariableGEPIndex &Src : SrcGEP.VarIndices) {
|
|
// Find V in Dest. This is N^2, but pointer indices almost never have more
|
|
// than a few variable indexes.
|
|
bool Found = false;
|
|
for (auto I : enumerate(DestGEP.VarIndices)) {
|
|
VariableGEPIndex &Dest = I.value();
|
|
if (!isValueEqualInPotentialCycles(Dest.Val.V, Src.Val.V) ||
|
|
!Dest.Val.hasSameCastsAs(Src.Val))
|
|
continue;
|
|
|
|
// If we found it, subtract off Scale V's from the entry in Dest. If it
|
|
// goes to zero, remove the entry.
|
|
if (Dest.Scale != Src.Scale) {
|
|
Dest.Scale -= Src.Scale;
|
|
Dest.IsNSW = false;
|
|
} else {
|
|
DestGEP.VarIndices.erase(DestGEP.VarIndices.begin() + I.index());
|
|
}
|
|
Found = true;
|
|
break;
|
|
}
|
|
|
|
// If we didn't consume this entry, add it to the end of the Dest list.
|
|
if (!Found) {
|
|
VariableGEPIndex Entry = {Src.Val, -Src.Scale, Src.CxtI, Src.IsNSW};
|
|
DestGEP.VarIndices.push_back(Entry);
|
|
}
|
|
}
|
|
}
|
|
|
|
bool BasicAAResult::constantOffsetHeuristic(
|
|
const DecomposedGEP &GEP, LocationSize MaybeV1Size,
|
|
LocationSize MaybeV2Size, AssumptionCache *AC, DominatorTree *DT) {
|
|
if (GEP.VarIndices.size() != 2 || !MaybeV1Size.hasValue() ||
|
|
!MaybeV2Size.hasValue())
|
|
return false;
|
|
|
|
const uint64_t V1Size = MaybeV1Size.getValue();
|
|
const uint64_t V2Size = MaybeV2Size.getValue();
|
|
|
|
const VariableGEPIndex &Var0 = GEP.VarIndices[0], &Var1 = GEP.VarIndices[1];
|
|
|
|
if (Var0.Val.TruncBits != 0 || !Var0.Val.hasSameCastsAs(Var1.Val) ||
|
|
Var0.Scale != -Var1.Scale ||
|
|
Var0.Val.V->getType() != Var1.Val.V->getType())
|
|
return false;
|
|
|
|
// We'll strip off the Extensions of Var0 and Var1 and do another round
|
|
// of GetLinearExpression decomposition. In the example above, if Var0
|
|
// is zext(%x + 1) we should get V1 == %x and V1Offset == 1.
|
|
|
|
LinearExpression E0 =
|
|
GetLinearExpression(CastedValue(Var0.Val.V), DL, 0, AC, DT);
|
|
LinearExpression E1 =
|
|
GetLinearExpression(CastedValue(Var1.Val.V), DL, 0, AC, DT);
|
|
if (E0.Scale != E1.Scale || !E0.Val.hasSameCastsAs(E1.Val) ||
|
|
!isValueEqualInPotentialCycles(E0.Val.V, E1.Val.V))
|
|
return false;
|
|
|
|
// We have a hit - Var0 and Var1 only differ by a constant offset!
|
|
|
|
// If we've been sext'ed then zext'd the maximum difference between Var0 and
|
|
// Var1 is possible to calculate, but we're just interested in the absolute
|
|
// minimum difference between the two. The minimum distance may occur due to
|
|
// wrapping; consider "add i3 %i, 5": if %i == 7 then 7 + 5 mod 8 == 4, and so
|
|
// the minimum distance between %i and %i + 5 is 3.
|
|
APInt MinDiff = E0.Offset - E1.Offset, Wrapped = -MinDiff;
|
|
MinDiff = APIntOps::umin(MinDiff, Wrapped);
|
|
APInt MinDiffBytes =
|
|
MinDiff.zextOrTrunc(Var0.Scale.getBitWidth()) * Var0.Scale.abs();
|
|
|
|
// We can't definitely say whether GEP1 is before or after V2 due to wrapping
|
|
// arithmetic (i.e. for some values of GEP1 and V2 GEP1 < V2, and for other
|
|
// values GEP1 > V2). We'll therefore only declare NoAlias if both V1Size and
|
|
// V2Size can fit in the MinDiffBytes gap.
|
|
return MinDiffBytes.uge(V1Size + GEP.Offset.abs()) &&
|
|
MinDiffBytes.uge(V2Size + GEP.Offset.abs());
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// BasicAliasAnalysis Pass
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
AnalysisKey BasicAA::Key;
|
|
|
|
BasicAAResult BasicAA::run(Function &F, FunctionAnalysisManager &AM) {
|
|
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
|
|
auto &AC = AM.getResult<AssumptionAnalysis>(F);
|
|
auto *DT = &AM.getResult<DominatorTreeAnalysis>(F);
|
|
auto *PV = AM.getCachedResult<PhiValuesAnalysis>(F);
|
|
return BasicAAResult(F.getParent()->getDataLayout(), F, TLI, AC, DT, PV);
|
|
}
|
|
|
|
BasicAAWrapperPass::BasicAAWrapperPass() : FunctionPass(ID) {
|
|
initializeBasicAAWrapperPassPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
char BasicAAWrapperPass::ID = 0;
|
|
|
|
void BasicAAWrapperPass::anchor() {}
|
|
|
|
INITIALIZE_PASS_BEGIN(BasicAAWrapperPass, "basic-aa",
|
|
"Basic Alias Analysis (stateless AA impl)", true, true)
|
|
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
|
|
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(PhiValuesWrapperPass)
|
|
INITIALIZE_PASS_END(BasicAAWrapperPass, "basic-aa",
|
|
"Basic Alias Analysis (stateless AA impl)", true, true)
|
|
|
|
FunctionPass *llvm::createBasicAAWrapperPass() {
|
|
return new BasicAAWrapperPass();
|
|
}
|
|
|
|
bool BasicAAWrapperPass::runOnFunction(Function &F) {
|
|
auto &ACT = getAnalysis<AssumptionCacheTracker>();
|
|
auto &TLIWP = getAnalysis<TargetLibraryInfoWrapperPass>();
|
|
auto &DTWP = getAnalysis<DominatorTreeWrapperPass>();
|
|
auto *PVWP = getAnalysisIfAvailable<PhiValuesWrapperPass>();
|
|
|
|
Result.reset(new BasicAAResult(F.getParent()->getDataLayout(), F,
|
|
TLIWP.getTLI(F), ACT.getAssumptionCache(F),
|
|
&DTWP.getDomTree(),
|
|
PVWP ? &PVWP->getResult() : nullptr));
|
|
|
|
return false;
|
|
}
|
|
|
|
void BasicAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.setPreservesAll();
|
|
AU.addRequiredTransitive<AssumptionCacheTracker>();
|
|
AU.addRequiredTransitive<DominatorTreeWrapperPass>();
|
|
AU.addRequiredTransitive<TargetLibraryInfoWrapperPass>();
|
|
AU.addUsedIfAvailable<PhiValuesWrapperPass>();
|
|
}
|
|
|
|
BasicAAResult llvm::createLegacyPMBasicAAResult(Pass &P, Function &F) {
|
|
return BasicAAResult(
|
|
F.getParent()->getDataLayout(), F,
|
|
P.getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F),
|
|
P.getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F));
|
|
}
|