1107 lines
42 KiB
C++
1107 lines
42 KiB
C++
//===- ArgumentPromotion.cpp - Promote by-reference arguments -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass promotes "by reference" arguments to be "by value" arguments. In
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// practice, this means looking for internal functions that have pointer
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// arguments. If it can prove, through the use of alias analysis, that an
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// argument is *only* loaded, then it can pass the value into the function
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// instead of the address of the value. This can cause recursive simplification
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// of code and lead to the elimination of allocas (especially in C++ template
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// code like the STL).
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//
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// This pass also handles aggregate arguments that are passed into a function,
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// scalarizing them if the elements of the aggregate are only loaded. Note that
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// by default it refuses to scalarize aggregates which would require passing in
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// more than three operands to the function, because passing thousands of
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// operands for a large array or structure is unprofitable! This limit can be
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// configured or disabled, however.
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//
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// Note that this transformation could also be done for arguments that are only
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// stored to (returning the value instead), but does not currently. This case
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// would be best handled when and if LLVM begins supporting multiple return
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// values from functions.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/IPO/ArgumentPromotion.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/None.h"
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#include "llvm/ADT/Optional.h"
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#include "llvm/ADT/STLExtras.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/ADT/StringExtras.h"
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#include "llvm/ADT/Twine.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/BasicAliasAnalysis.h"
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#include "llvm/Analysis/CGSCCPassManager.h"
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#include "llvm/Analysis/CallGraph.h"
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#include "llvm/Analysis/CallGraphSCCPass.h"
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#include "llvm/Analysis/LazyCallGraph.h"
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#include "llvm/Analysis/Loads.h"
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#include "llvm/Analysis/MemoryLocation.h"
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#include "llvm/Analysis/TargetLibraryInfo.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/BasicBlock.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/CallSite.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/Function.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/Metadata.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/PassManager.h"
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#include "llvm/IR/Type.h"
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#include "llvm/IR/Use.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/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/IPO.h"
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#include <algorithm>
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#include <cassert>
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#include <cstdint>
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#include <functional>
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#include <iterator>
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#include <map>
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#include <set>
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#include <string>
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#include <utility>
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#include <vector>
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using namespace llvm;
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#define DEBUG_TYPE "argpromotion"
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STATISTIC(NumArgumentsPromoted, "Number of pointer arguments promoted");
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STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted");
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STATISTIC(NumByValArgsPromoted, "Number of byval arguments promoted");
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STATISTIC(NumArgumentsDead, "Number of dead pointer args eliminated");
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/// A vector used to hold the indices of a single GEP instruction
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using IndicesVector = std::vector<uint64_t>;
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/// DoPromotion - This method actually performs the promotion of the specified
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/// arguments, and returns the new function. At this point, we know that it's
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/// safe to do so.
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static Function *
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doPromotion(Function *F, SmallPtrSetImpl<Argument *> &ArgsToPromote,
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SmallPtrSetImpl<Argument *> &ByValArgsToTransform,
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Optional<function_ref<void(CallSite OldCS, CallSite NewCS)>>
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ReplaceCallSite) {
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// Start by computing a new prototype for the function, which is the same as
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// the old function, but has modified arguments.
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FunctionType *FTy = F->getFunctionType();
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std::vector<Type *> Params;
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using ScalarizeTable = std::set<std::pair<Type *, IndicesVector>>;
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// ScalarizedElements - If we are promoting a pointer that has elements
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// accessed out of it, keep track of which elements are accessed so that we
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// can add one argument for each.
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//
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// Arguments that are directly loaded will have a zero element value here, to
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// handle cases where there are both a direct load and GEP accesses.
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std::map<Argument *, ScalarizeTable> ScalarizedElements;
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// OriginalLoads - Keep track of a representative load instruction from the
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// original function so that we can tell the alias analysis implementation
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// what the new GEP/Load instructions we are inserting look like.
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// We need to keep the original loads for each argument and the elements
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// of the argument that are accessed.
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std::map<std::pair<Argument *, IndicesVector>, LoadInst *> OriginalLoads;
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// Attribute - Keep track of the parameter attributes for the arguments
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// that we are *not* promoting. For the ones that we do promote, the parameter
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// attributes are lost
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SmallVector<AttributeSet, 8> ArgAttrVec;
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AttributeList PAL = F->getAttributes();
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// First, determine the new argument list
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unsigned ArgNo = 0;
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for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
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++I, ++ArgNo) {
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if (ByValArgsToTransform.count(&*I)) {
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// Simple byval argument? Just add all the struct element types.
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Type *AgTy = cast<PointerType>(I->getType())->getElementType();
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StructType *STy = cast<StructType>(AgTy);
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Params.insert(Params.end(), STy->element_begin(), STy->element_end());
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ArgAttrVec.insert(ArgAttrVec.end(), STy->getNumElements(),
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AttributeSet());
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++NumByValArgsPromoted;
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} else if (!ArgsToPromote.count(&*I)) {
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// Unchanged argument
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Params.push_back(I->getType());
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ArgAttrVec.push_back(PAL.getParamAttributes(ArgNo));
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} else if (I->use_empty()) {
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// Dead argument (which are always marked as promotable)
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++NumArgumentsDead;
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// There may be remaining metadata uses of the argument for things like
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// llvm.dbg.value. Replace them with undef.
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I->replaceAllUsesWith(UndefValue::get(I->getType()));
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} else {
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// Okay, this is being promoted. This means that the only uses are loads
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// or GEPs which are only used by loads
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// In this table, we will track which indices are loaded from the argument
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// (where direct loads are tracked as no indices).
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ScalarizeTable &ArgIndices = ScalarizedElements[&*I];
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for (User *U : I->users()) {
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Instruction *UI = cast<Instruction>(U);
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Type *SrcTy;
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if (LoadInst *L = dyn_cast<LoadInst>(UI))
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SrcTy = L->getType();
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else
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SrcTy = cast<GetElementPtrInst>(UI)->getSourceElementType();
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IndicesVector Indices;
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Indices.reserve(UI->getNumOperands() - 1);
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// Since loads will only have a single operand, and GEPs only a single
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// non-index operand, this will record direct loads without any indices,
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// and gep+loads with the GEP indices.
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for (User::op_iterator II = UI->op_begin() + 1, IE = UI->op_end();
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II != IE; ++II)
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Indices.push_back(cast<ConstantInt>(*II)->getSExtValue());
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// GEPs with a single 0 index can be merged with direct loads
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if (Indices.size() == 1 && Indices.front() == 0)
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Indices.clear();
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ArgIndices.insert(std::make_pair(SrcTy, Indices));
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LoadInst *OrigLoad;
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if (LoadInst *L = dyn_cast<LoadInst>(UI))
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OrigLoad = L;
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else
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// Take any load, we will use it only to update Alias Analysis
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OrigLoad = cast<LoadInst>(UI->user_back());
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OriginalLoads[std::make_pair(&*I, Indices)] = OrigLoad;
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}
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// Add a parameter to the function for each element passed in.
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for (const auto &ArgIndex : ArgIndices) {
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// not allowed to dereference ->begin() if size() is 0
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Params.push_back(GetElementPtrInst::getIndexedType(
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cast<PointerType>(I->getType()->getScalarType())->getElementType(),
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ArgIndex.second));
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ArgAttrVec.push_back(AttributeSet());
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assert(Params.back());
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}
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if (ArgIndices.size() == 1 && ArgIndices.begin()->second.empty())
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++NumArgumentsPromoted;
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else
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++NumAggregatesPromoted;
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}
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}
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Type *RetTy = FTy->getReturnType();
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// Construct the new function type using the new arguments.
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FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
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// Create the new function body and insert it into the module.
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Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName());
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NF->copyAttributesFrom(F);
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// Patch the pointer to LLVM function in debug info descriptor.
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NF->setSubprogram(F->getSubprogram());
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F->setSubprogram(nullptr);
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LLVM_DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n"
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<< "From: " << *F);
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// Recompute the parameter attributes list based on the new arguments for
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// the function.
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NF->setAttributes(AttributeList::get(F->getContext(), PAL.getFnAttributes(),
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PAL.getRetAttributes(), ArgAttrVec));
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ArgAttrVec.clear();
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F->getParent()->getFunctionList().insert(F->getIterator(), NF);
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NF->takeName(F);
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// Loop over all of the callers of the function, transforming the call sites
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// to pass in the loaded pointers.
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//
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SmallVector<Value *, 16> Args;
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while (!F->use_empty()) {
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CallSite CS(F->user_back());
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assert(CS.getCalledFunction() == F);
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Instruction *Call = CS.getInstruction();
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const AttributeList &CallPAL = CS.getAttributes();
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// Loop over the operands, inserting GEP and loads in the caller as
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// appropriate.
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CallSite::arg_iterator AI = CS.arg_begin();
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ArgNo = 0;
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for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
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++I, ++AI, ++ArgNo)
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if (!ArgsToPromote.count(&*I) && !ByValArgsToTransform.count(&*I)) {
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Args.push_back(*AI); // Unmodified argument
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ArgAttrVec.push_back(CallPAL.getParamAttributes(ArgNo));
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} else if (ByValArgsToTransform.count(&*I)) {
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// Emit a GEP and load for each element of the struct.
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Type *AgTy = cast<PointerType>(I->getType())->getElementType();
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StructType *STy = cast<StructType>(AgTy);
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Value *Idxs[2] = {
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ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr};
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for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
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Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
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Value *Idx = GetElementPtrInst::Create(
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STy, *AI, Idxs, (*AI)->getName() + "." + Twine(i), Call);
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// TODO: Tell AA about the new values?
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Args.push_back(new LoadInst(Idx, Idx->getName() + ".val", Call));
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ArgAttrVec.push_back(AttributeSet());
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}
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} else if (!I->use_empty()) {
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// Non-dead argument: insert GEPs and loads as appropriate.
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ScalarizeTable &ArgIndices = ScalarizedElements[&*I];
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// Store the Value* version of the indices in here, but declare it now
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// for reuse.
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std::vector<Value *> Ops;
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for (const auto &ArgIndex : ArgIndices) {
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Value *V = *AI;
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LoadInst *OrigLoad =
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OriginalLoads[std::make_pair(&*I, ArgIndex.second)];
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if (!ArgIndex.second.empty()) {
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Ops.reserve(ArgIndex.second.size());
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Type *ElTy = V->getType();
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for (auto II : ArgIndex.second) {
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// Use i32 to index structs, and i64 for others (pointers/arrays).
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// This satisfies GEP constraints.
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Type *IdxTy =
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(ElTy->isStructTy() ? Type::getInt32Ty(F->getContext())
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: Type::getInt64Ty(F->getContext()));
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Ops.push_back(ConstantInt::get(IdxTy, II));
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// Keep track of the type we're currently indexing.
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if (auto *ElPTy = dyn_cast<PointerType>(ElTy))
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ElTy = ElPTy->getElementType();
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else
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ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(II);
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}
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// And create a GEP to extract those indices.
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V = GetElementPtrInst::Create(ArgIndex.first, V, Ops,
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V->getName() + ".idx", Call);
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Ops.clear();
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}
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// Since we're replacing a load make sure we take the alignment
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// of the previous load.
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LoadInst *newLoad = new LoadInst(V, V->getName() + ".val", Call);
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newLoad->setAlignment(OrigLoad->getAlignment());
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// Transfer the AA info too.
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AAMDNodes AAInfo;
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OrigLoad->getAAMetadata(AAInfo);
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newLoad->setAAMetadata(AAInfo);
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Args.push_back(newLoad);
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ArgAttrVec.push_back(AttributeSet());
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}
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}
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// Push any varargs arguments on the list.
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for (; AI != CS.arg_end(); ++AI, ++ArgNo) {
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Args.push_back(*AI);
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ArgAttrVec.push_back(CallPAL.getParamAttributes(ArgNo));
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}
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SmallVector<OperandBundleDef, 1> OpBundles;
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CS.getOperandBundlesAsDefs(OpBundles);
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CallSite NewCS;
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if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
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NewCS = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
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Args, OpBundles, "", Call);
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} else {
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auto *NewCall = CallInst::Create(NF, Args, OpBundles, "", Call);
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NewCall->setTailCallKind(cast<CallInst>(Call)->getTailCallKind());
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NewCS = NewCall;
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}
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NewCS.setCallingConv(CS.getCallingConv());
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NewCS.setAttributes(
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AttributeList::get(F->getContext(), CallPAL.getFnAttributes(),
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CallPAL.getRetAttributes(), ArgAttrVec));
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NewCS->setDebugLoc(Call->getDebugLoc());
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uint64_t W;
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if (Call->extractProfTotalWeight(W))
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NewCS->setProfWeight(W);
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Args.clear();
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ArgAttrVec.clear();
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// Update the callgraph to know that the callsite has been transformed.
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if (ReplaceCallSite)
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(*ReplaceCallSite)(CS, NewCS);
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if (!Call->use_empty()) {
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Call->replaceAllUsesWith(NewCS.getInstruction());
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NewCS->takeName(Call);
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}
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// Finally, remove the old call from the program, reducing the use-count of
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// F.
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Call->eraseFromParent();
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}
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const DataLayout &DL = F->getParent()->getDataLayout();
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// Since we have now created the new function, splice the body of the old
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// function right into the new function, leaving the old rotting hulk of the
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// function empty.
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NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
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// Loop over the argument list, transferring uses of the old arguments over to
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// the new arguments, also transferring over the names as well.
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for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
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I2 = NF->arg_begin();
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I != E; ++I) {
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if (!ArgsToPromote.count(&*I) && !ByValArgsToTransform.count(&*I)) {
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// If this is an unmodified argument, move the name and users over to the
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// new version.
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I->replaceAllUsesWith(&*I2);
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I2->takeName(&*I);
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++I2;
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continue;
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}
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if (ByValArgsToTransform.count(&*I)) {
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// In the callee, we create an alloca, and store each of the new incoming
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// arguments into the alloca.
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Instruction *InsertPt = &NF->begin()->front();
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// Just add all the struct element types.
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Type *AgTy = cast<PointerType>(I->getType())->getElementType();
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Value *TheAlloca = new AllocaInst(AgTy, DL.getAllocaAddrSpace(), nullptr,
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I->getParamAlignment(), "", InsertPt);
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StructType *STy = cast<StructType>(AgTy);
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Value *Idxs[2] = {ConstantInt::get(Type::getInt32Ty(F->getContext()), 0),
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nullptr};
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for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
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Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
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Value *Idx = GetElementPtrInst::Create(
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AgTy, TheAlloca, Idxs, TheAlloca->getName() + "." + Twine(i),
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InsertPt);
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I2->setName(I->getName() + "." + Twine(i));
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new StoreInst(&*I2++, Idx, InsertPt);
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}
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// Anything that used the arg should now use the alloca.
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I->replaceAllUsesWith(TheAlloca);
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TheAlloca->takeName(&*I);
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// If the alloca is used in a call, we must clear the tail flag since
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// the callee now uses an alloca from the caller.
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for (User *U : TheAlloca->users()) {
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CallInst *Call = dyn_cast<CallInst>(U);
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if (!Call)
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continue;
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Call->setTailCall(false);
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}
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continue;
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}
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if (I->use_empty())
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continue;
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// Otherwise, if we promoted this argument, then all users are load
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// instructions (or GEPs with only load users), and all loads should be
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// using the new argument that we added.
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ScalarizeTable &ArgIndices = ScalarizedElements[&*I];
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while (!I->use_empty()) {
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if (LoadInst *LI = dyn_cast<LoadInst>(I->user_back())) {
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assert(ArgIndices.begin()->second.empty() &&
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"Load element should sort to front!");
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I2->setName(I->getName() + ".val");
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LI->replaceAllUsesWith(&*I2);
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LI->eraseFromParent();
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LLVM_DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName()
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<< "' in function '" << F->getName() << "'\n");
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} else {
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GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->user_back());
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IndicesVector Operands;
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Operands.reserve(GEP->getNumIndices());
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for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
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II != IE; ++II)
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Operands.push_back(cast<ConstantInt>(*II)->getSExtValue());
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// GEPs with a single 0 index can be merged with direct loads
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if (Operands.size() == 1 && Operands.front() == 0)
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Operands.clear();
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Function::arg_iterator TheArg = I2;
|
|
for (ScalarizeTable::iterator It = ArgIndices.begin();
|
|
It->second != Operands; ++It, ++TheArg) {
|
|
assert(It != ArgIndices.end() && "GEP not handled??");
|
|
}
|
|
|
|
std::string NewName = I->getName();
|
|
for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
|
|
NewName += "." + utostr(Operands[i]);
|
|
}
|
|
NewName += ".val";
|
|
TheArg->setName(NewName);
|
|
|
|
LLVM_DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName()
|
|
<< "' of function '" << NF->getName() << "'\n");
|
|
|
|
// All of the uses must be load instructions. Replace them all with
|
|
// the argument specified by ArgNo.
|
|
while (!GEP->use_empty()) {
|
|
LoadInst *L = cast<LoadInst>(GEP->user_back());
|
|
L->replaceAllUsesWith(&*TheArg);
|
|
L->eraseFromParent();
|
|
}
|
|
GEP->eraseFromParent();
|
|
}
|
|
}
|
|
|
|
// Increment I2 past all of the arguments added for this promoted pointer.
|
|
std::advance(I2, ArgIndices.size());
|
|
}
|
|
|
|
return NF;
|
|
}
|
|
|
|
/// AllCallersPassInValidPointerForArgument - Return true if we can prove that
|
|
/// all callees pass in a valid pointer for the specified function argument.
|
|
static bool allCallersPassInValidPointerForArgument(Argument *Arg) {
|
|
Function *Callee = Arg->getParent();
|
|
const DataLayout &DL = Callee->getParent()->getDataLayout();
|
|
|
|
unsigned ArgNo = Arg->getArgNo();
|
|
|
|
// Look at all call sites of the function. At this point we know we only have
|
|
// direct callees.
|
|
for (User *U : Callee->users()) {
|
|
CallSite CS(U);
|
|
assert(CS && "Should only have direct calls!");
|
|
|
|
if (!isDereferenceablePointer(CS.getArgument(ArgNo), DL))
|
|
return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// Returns true if Prefix is a prefix of longer. That means, Longer has a size
|
|
/// that is greater than or equal to the size of prefix, and each of the
|
|
/// elements in Prefix is the same as the corresponding elements in Longer.
|
|
///
|
|
/// This means it also returns true when Prefix and Longer are equal!
|
|
static bool isPrefix(const IndicesVector &Prefix, const IndicesVector &Longer) {
|
|
if (Prefix.size() > Longer.size())
|
|
return false;
|
|
return std::equal(Prefix.begin(), Prefix.end(), Longer.begin());
|
|
}
|
|
|
|
/// Checks if Indices, or a prefix of Indices, is in Set.
|
|
static bool prefixIn(const IndicesVector &Indices,
|
|
std::set<IndicesVector> &Set) {
|
|
std::set<IndicesVector>::iterator Low;
|
|
Low = Set.upper_bound(Indices);
|
|
if (Low != Set.begin())
|
|
Low--;
|
|
// Low is now the last element smaller than or equal to Indices. This means
|
|
// it points to a prefix of Indices (possibly Indices itself), if such
|
|
// prefix exists.
|
|
//
|
|
// This load is safe if any prefix of its operands is safe to load.
|
|
return Low != Set.end() && isPrefix(*Low, Indices);
|
|
}
|
|
|
|
/// Mark the given indices (ToMark) as safe in the given set of indices
|
|
/// (Safe). Marking safe usually means adding ToMark to Safe. However, if there
|
|
/// is already a prefix of Indices in Safe, Indices are implicitely marked safe
|
|
/// already. Furthermore, any indices that Indices is itself a prefix of, are
|
|
/// removed from Safe (since they are implicitely safe because of Indices now).
|
|
static void markIndicesSafe(const IndicesVector &ToMark,
|
|
std::set<IndicesVector> &Safe) {
|
|
std::set<IndicesVector>::iterator Low;
|
|
Low = Safe.upper_bound(ToMark);
|
|
// Guard against the case where Safe is empty
|
|
if (Low != Safe.begin())
|
|
Low--;
|
|
// Low is now the last element smaller than or equal to Indices. This
|
|
// means it points to a prefix of Indices (possibly Indices itself), if
|
|
// such prefix exists.
|
|
if (Low != Safe.end()) {
|
|
if (isPrefix(*Low, ToMark))
|
|
// If there is already a prefix of these indices (or exactly these
|
|
// indices) marked a safe, don't bother adding these indices
|
|
return;
|
|
|
|
// Increment Low, so we can use it as a "insert before" hint
|
|
++Low;
|
|
}
|
|
// Insert
|
|
Low = Safe.insert(Low, ToMark);
|
|
++Low;
|
|
// If there we're a prefix of longer index list(s), remove those
|
|
std::set<IndicesVector>::iterator End = Safe.end();
|
|
while (Low != End && isPrefix(ToMark, *Low)) {
|
|
std::set<IndicesVector>::iterator Remove = Low;
|
|
++Low;
|
|
Safe.erase(Remove);
|
|
}
|
|
}
|
|
|
|
/// isSafeToPromoteArgument - As you might guess from the name of this method,
|
|
/// it checks to see if it is both safe and useful to promote the argument.
|
|
/// This method limits promotion of aggregates to only promote up to three
|
|
/// elements of the aggregate in order to avoid exploding the number of
|
|
/// arguments passed in.
|
|
static bool isSafeToPromoteArgument(Argument *Arg, bool isByValOrInAlloca,
|
|
AAResults &AAR, unsigned MaxElements) {
|
|
using GEPIndicesSet = std::set<IndicesVector>;
|
|
|
|
// Quick exit for unused arguments
|
|
if (Arg->use_empty())
|
|
return true;
|
|
|
|
// We can only promote this argument if all of the uses are loads, or are GEP
|
|
// instructions (with constant indices) that are subsequently loaded.
|
|
//
|
|
// Promoting the argument causes it to be loaded in the caller
|
|
// unconditionally. This is only safe if we can prove that either the load
|
|
// would have happened in the callee anyway (ie, there is a load in the entry
|
|
// block) or the pointer passed in at every call site is guaranteed to be
|
|
// valid.
|
|
// In the former case, invalid loads can happen, but would have happened
|
|
// anyway, in the latter case, invalid loads won't happen. This prevents us
|
|
// from introducing an invalid load that wouldn't have happened in the
|
|
// original code.
|
|
//
|
|
// This set will contain all sets of indices that are loaded in the entry
|
|
// block, and thus are safe to unconditionally load in the caller.
|
|
//
|
|
// This optimization is also safe for InAlloca parameters, because it verifies
|
|
// that the address isn't captured.
|
|
GEPIndicesSet SafeToUnconditionallyLoad;
|
|
|
|
// This set contains all the sets of indices that we are planning to promote.
|
|
// This makes it possible to limit the number of arguments added.
|
|
GEPIndicesSet ToPromote;
|
|
|
|
// If the pointer is always valid, any load with first index 0 is valid.
|
|
if (isByValOrInAlloca || allCallersPassInValidPointerForArgument(Arg))
|
|
SafeToUnconditionallyLoad.insert(IndicesVector(1, 0));
|
|
|
|
// First, iterate the entry block and mark loads of (geps of) arguments as
|
|
// safe.
|
|
BasicBlock &EntryBlock = Arg->getParent()->front();
|
|
// Declare this here so we can reuse it
|
|
IndicesVector Indices;
|
|
for (Instruction &I : EntryBlock)
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
|
|
Value *V = LI->getPointerOperand();
|
|
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
|
|
V = GEP->getPointerOperand();
|
|
if (V == Arg) {
|
|
// This load actually loads (part of) Arg? Check the indices then.
|
|
Indices.reserve(GEP->getNumIndices());
|
|
for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
|
|
II != IE; ++II)
|
|
if (ConstantInt *CI = dyn_cast<ConstantInt>(*II))
|
|
Indices.push_back(CI->getSExtValue());
|
|
else
|
|
// We found a non-constant GEP index for this argument? Bail out
|
|
// right away, can't promote this argument at all.
|
|
return false;
|
|
|
|
// Indices checked out, mark them as safe
|
|
markIndicesSafe(Indices, SafeToUnconditionallyLoad);
|
|
Indices.clear();
|
|
}
|
|
} else if (V == Arg) {
|
|
// Direct loads are equivalent to a GEP with a single 0 index.
|
|
markIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad);
|
|
}
|
|
}
|
|
|
|
// Now, iterate all uses of the argument to see if there are any uses that are
|
|
// not (GEP+)loads, or any (GEP+)loads that are not safe to promote.
|
|
SmallVector<LoadInst *, 16> Loads;
|
|
IndicesVector Operands;
|
|
for (Use &U : Arg->uses()) {
|
|
User *UR = U.getUser();
|
|
Operands.clear();
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(UR)) {
|
|
// Don't hack volatile/atomic loads
|
|
if (!LI->isSimple())
|
|
return false;
|
|
Loads.push_back(LI);
|
|
// Direct loads are equivalent to a GEP with a zero index and then a load.
|
|
Operands.push_back(0);
|
|
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(UR)) {
|
|
if (GEP->use_empty()) {
|
|
// Dead GEP's cause trouble later. Just remove them if we run into
|
|
// them.
|
|
GEP->eraseFromParent();
|
|
// TODO: This runs the above loop over and over again for dead GEPs
|
|
// Couldn't we just do increment the UI iterator earlier and erase the
|
|
// use?
|
|
return isSafeToPromoteArgument(Arg, isByValOrInAlloca, AAR,
|
|
MaxElements);
|
|
}
|
|
|
|
// Ensure that all of the indices are constants.
|
|
for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); i != e;
|
|
++i)
|
|
if (ConstantInt *C = dyn_cast<ConstantInt>(*i))
|
|
Operands.push_back(C->getSExtValue());
|
|
else
|
|
return false; // Not a constant operand GEP!
|
|
|
|
// Ensure that the only users of the GEP are load instructions.
|
|
for (User *GEPU : GEP->users())
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(GEPU)) {
|
|
// Don't hack volatile/atomic loads
|
|
if (!LI->isSimple())
|
|
return false;
|
|
Loads.push_back(LI);
|
|
} else {
|
|
// Other uses than load?
|
|
return false;
|
|
}
|
|
} else {
|
|
return false; // Not a load or a GEP.
|
|
}
|
|
|
|
// Now, see if it is safe to promote this load / loads of this GEP. Loading
|
|
// is safe if Operands, or a prefix of Operands, is marked as safe.
|
|
if (!prefixIn(Operands, SafeToUnconditionallyLoad))
|
|
return false;
|
|
|
|
// See if we are already promoting a load with these indices. If not, check
|
|
// to make sure that we aren't promoting too many elements. If so, nothing
|
|
// to do.
|
|
if (ToPromote.find(Operands) == ToPromote.end()) {
|
|
if (MaxElements > 0 && ToPromote.size() == MaxElements) {
|
|
LLVM_DEBUG(dbgs() << "argpromotion not promoting argument '"
|
|
<< Arg->getName()
|
|
<< "' because it would require adding more "
|
|
<< "than " << MaxElements
|
|
<< " arguments to the function.\n");
|
|
// We limit aggregate promotion to only promoting up to a fixed number
|
|
// of elements of the aggregate.
|
|
return false;
|
|
}
|
|
ToPromote.insert(std::move(Operands));
|
|
}
|
|
}
|
|
|
|
if (Loads.empty())
|
|
return true; // No users, this is a dead argument.
|
|
|
|
// Okay, now we know that the argument is only used by load instructions and
|
|
// it is safe to unconditionally perform all of them. Use alias analysis to
|
|
// check to see if the pointer is guaranteed to not be modified from entry of
|
|
// the function to each of the load instructions.
|
|
|
|
// Because there could be several/many load instructions, remember which
|
|
// blocks we know to be transparent to the load.
|
|
df_iterator_default_set<BasicBlock *, 16> TranspBlocks;
|
|
|
|
for (LoadInst *Load : Loads) {
|
|
// Check to see if the load is invalidated from the start of the block to
|
|
// the load itself.
|
|
BasicBlock *BB = Load->getParent();
|
|
|
|
MemoryLocation Loc = MemoryLocation::get(Load);
|
|
if (AAR.canInstructionRangeModRef(BB->front(), *Load, Loc, ModRefInfo::Mod))
|
|
return false; // Pointer is invalidated!
|
|
|
|
// Now check every path from the entry block to the load for transparency.
|
|
// To do this, we perform a depth first search on the inverse CFG from the
|
|
// loading block.
|
|
for (BasicBlock *P : predecessors(BB)) {
|
|
for (BasicBlock *TranspBB : inverse_depth_first_ext(P, TranspBlocks))
|
|
if (AAR.canBasicBlockModify(*TranspBB, Loc))
|
|
return false;
|
|
}
|
|
}
|
|
|
|
// If the path from the entry of the function to each load is free of
|
|
// instructions that potentially invalidate the load, we can make the
|
|
// transformation!
|
|
return true;
|
|
}
|
|
|
|
/// Checks if a type could have padding bytes.
|
|
static bool isDenselyPacked(Type *type, const DataLayout &DL) {
|
|
// There is no size information, so be conservative.
|
|
if (!type->isSized())
|
|
return false;
|
|
|
|
// If the alloc size is not equal to the storage size, then there are padding
|
|
// bytes. For x86_fp80 on x86-64, size: 80 alloc size: 128.
|
|
if (DL.getTypeSizeInBits(type) != DL.getTypeAllocSizeInBits(type))
|
|
return false;
|
|
|
|
if (!isa<CompositeType>(type))
|
|
return true;
|
|
|
|
// For homogenous sequential types, check for padding within members.
|
|
if (SequentialType *seqTy = dyn_cast<SequentialType>(type))
|
|
return isDenselyPacked(seqTy->getElementType(), DL);
|
|
|
|
// Check for padding within and between elements of a struct.
|
|
StructType *StructTy = cast<StructType>(type);
|
|
const StructLayout *Layout = DL.getStructLayout(StructTy);
|
|
uint64_t StartPos = 0;
|
|
for (unsigned i = 0, E = StructTy->getNumElements(); i < E; ++i) {
|
|
Type *ElTy = StructTy->getElementType(i);
|
|
if (!isDenselyPacked(ElTy, DL))
|
|
return false;
|
|
if (StartPos != Layout->getElementOffsetInBits(i))
|
|
return false;
|
|
StartPos += DL.getTypeAllocSizeInBits(ElTy);
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/// Checks if the padding bytes of an argument could be accessed.
|
|
static bool canPaddingBeAccessed(Argument *arg) {
|
|
assert(arg->hasByValAttr());
|
|
|
|
// Track all the pointers to the argument to make sure they are not captured.
|
|
SmallPtrSet<Value *, 16> PtrValues;
|
|
PtrValues.insert(arg);
|
|
|
|
// Track all of the stores.
|
|
SmallVector<StoreInst *, 16> Stores;
|
|
|
|
// Scan through the uses recursively to make sure the pointer is always used
|
|
// sanely.
|
|
SmallVector<Value *, 16> WorkList;
|
|
WorkList.insert(WorkList.end(), arg->user_begin(), arg->user_end());
|
|
while (!WorkList.empty()) {
|
|
Value *V = WorkList.back();
|
|
WorkList.pop_back();
|
|
if (isa<GetElementPtrInst>(V) || isa<PHINode>(V)) {
|
|
if (PtrValues.insert(V).second)
|
|
WorkList.insert(WorkList.end(), V->user_begin(), V->user_end());
|
|
} else if (StoreInst *Store = dyn_cast<StoreInst>(V)) {
|
|
Stores.push_back(Store);
|
|
} else if (!isa<LoadInst>(V)) {
|
|
return true;
|
|
}
|
|
}
|
|
|
|
// Check to make sure the pointers aren't captured
|
|
for (StoreInst *Store : Stores)
|
|
if (PtrValues.count(Store->getValueOperand()))
|
|
return true;
|
|
|
|
return false;
|
|
}
|
|
|
|
/// PromoteArguments - This method checks the specified function to see if there
|
|
/// are any promotable arguments and if it is safe to promote the function (for
|
|
/// example, all callers are direct). If safe to promote some arguments, it
|
|
/// calls the DoPromotion method.
|
|
static Function *
|
|
promoteArguments(Function *F, function_ref<AAResults &(Function &F)> AARGetter,
|
|
unsigned MaxElements,
|
|
Optional<function_ref<void(CallSite OldCS, CallSite NewCS)>>
|
|
ReplaceCallSite) {
|
|
// Don't perform argument promotion for naked functions; otherwise we can end
|
|
// up removing parameters that are seemingly 'not used' as they are referred
|
|
// to in the assembly.
|
|
if(F->hasFnAttribute(Attribute::Naked))
|
|
return nullptr;
|
|
|
|
// Make sure that it is local to this module.
|
|
if (!F->hasLocalLinkage())
|
|
return nullptr;
|
|
|
|
// Don't promote arguments for variadic functions. Adding, removing, or
|
|
// changing non-pack parameters can change the classification of pack
|
|
// parameters. Frontends encode that classification at the call site in the
|
|
// IR, while in the callee the classification is determined dynamically based
|
|
// on the number of registers consumed so far.
|
|
if (F->isVarArg())
|
|
return nullptr;
|
|
|
|
// First check: see if there are any pointer arguments! If not, quick exit.
|
|
SmallVector<Argument *, 16> PointerArgs;
|
|
for (Argument &I : F->args())
|
|
if (I.getType()->isPointerTy())
|
|
PointerArgs.push_back(&I);
|
|
if (PointerArgs.empty())
|
|
return nullptr;
|
|
|
|
// Second check: make sure that all callers are direct callers. We can't
|
|
// transform functions that have indirect callers. Also see if the function
|
|
// is self-recursive.
|
|
bool isSelfRecursive = false;
|
|
for (Use &U : F->uses()) {
|
|
CallSite CS(U.getUser());
|
|
// Must be a direct call.
|
|
if (CS.getInstruction() == nullptr || !CS.isCallee(&U))
|
|
return nullptr;
|
|
|
|
// Can't change signature of musttail callee
|
|
if (CS.isMustTailCall())
|
|
return nullptr;
|
|
|
|
if (CS.getInstruction()->getParent()->getParent() == F)
|
|
isSelfRecursive = true;
|
|
}
|
|
|
|
// Can't change signature of musttail caller
|
|
// FIXME: Support promoting whole chain of musttail functions
|
|
for (BasicBlock &BB : *F)
|
|
if (BB.getTerminatingMustTailCall())
|
|
return nullptr;
|
|
|
|
const DataLayout &DL = F->getParent()->getDataLayout();
|
|
|
|
AAResults &AAR = AARGetter(*F);
|
|
|
|
// Check to see which arguments are promotable. If an argument is promotable,
|
|
// add it to ArgsToPromote.
|
|
SmallPtrSet<Argument *, 8> ArgsToPromote;
|
|
SmallPtrSet<Argument *, 8> ByValArgsToTransform;
|
|
for (Argument *PtrArg : PointerArgs) {
|
|
Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();
|
|
|
|
// Replace sret attribute with noalias. This reduces register pressure by
|
|
// avoiding a register copy.
|
|
if (PtrArg->hasStructRetAttr()) {
|
|
unsigned ArgNo = PtrArg->getArgNo();
|
|
F->removeParamAttr(ArgNo, Attribute::StructRet);
|
|
F->addParamAttr(ArgNo, Attribute::NoAlias);
|
|
for (Use &U : F->uses()) {
|
|
CallSite CS(U.getUser());
|
|
CS.removeParamAttr(ArgNo, Attribute::StructRet);
|
|
CS.addParamAttr(ArgNo, Attribute::NoAlias);
|
|
}
|
|
}
|
|
|
|
// If this is a byval argument, and if the aggregate type is small, just
|
|
// pass the elements, which is always safe, if the passed value is densely
|
|
// packed or if we can prove the padding bytes are never accessed. This does
|
|
// not apply to inalloca.
|
|
bool isSafeToPromote =
|
|
PtrArg->hasByValAttr() &&
|
|
(isDenselyPacked(AgTy, DL) || !canPaddingBeAccessed(PtrArg));
|
|
if (isSafeToPromote) {
|
|
if (StructType *STy = dyn_cast<StructType>(AgTy)) {
|
|
if (MaxElements > 0 && STy->getNumElements() > MaxElements) {
|
|
LLVM_DEBUG(dbgs() << "argpromotion disable promoting argument '"
|
|
<< PtrArg->getName()
|
|
<< "' because it would require adding more"
|
|
<< " than " << MaxElements
|
|
<< " arguments to the function.\n");
|
|
continue;
|
|
}
|
|
|
|
// If all the elements are single-value types, we can promote it.
|
|
bool AllSimple = true;
|
|
for (const auto *EltTy : STy->elements()) {
|
|
if (!EltTy->isSingleValueType()) {
|
|
AllSimple = false;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Safe to transform, don't even bother trying to "promote" it.
|
|
// Passing the elements as a scalar will allow sroa to hack on
|
|
// the new alloca we introduce.
|
|
if (AllSimple) {
|
|
ByValArgsToTransform.insert(PtrArg);
|
|
continue;
|
|
}
|
|
}
|
|
}
|
|
|
|
// If the argument is a recursive type and we're in a recursive
|
|
// function, we could end up infinitely peeling the function argument.
|
|
if (isSelfRecursive) {
|
|
if (StructType *STy = dyn_cast<StructType>(AgTy)) {
|
|
bool RecursiveType = false;
|
|
for (const auto *EltTy : STy->elements()) {
|
|
if (EltTy == PtrArg->getType()) {
|
|
RecursiveType = true;
|
|
break;
|
|
}
|
|
}
|
|
if (RecursiveType)
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// Otherwise, see if we can promote the pointer to its value.
|
|
if (isSafeToPromoteArgument(PtrArg, PtrArg->hasByValOrInAllocaAttr(), AAR,
|
|
MaxElements))
|
|
ArgsToPromote.insert(PtrArg);
|
|
}
|
|
|
|
// No promotable pointer arguments.
|
|
if (ArgsToPromote.empty() && ByValArgsToTransform.empty())
|
|
return nullptr;
|
|
|
|
return doPromotion(F, ArgsToPromote, ByValArgsToTransform, ReplaceCallSite);
|
|
}
|
|
|
|
PreservedAnalyses ArgumentPromotionPass::run(LazyCallGraph::SCC &C,
|
|
CGSCCAnalysisManager &AM,
|
|
LazyCallGraph &CG,
|
|
CGSCCUpdateResult &UR) {
|
|
bool Changed = false, LocalChange;
|
|
|
|
// Iterate until we stop promoting from this SCC.
|
|
do {
|
|
LocalChange = false;
|
|
|
|
for (LazyCallGraph::Node &N : C) {
|
|
Function &OldF = N.getFunction();
|
|
|
|
FunctionAnalysisManager &FAM =
|
|
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C, CG).getManager();
|
|
// FIXME: This lambda must only be used with this function. We should
|
|
// skip the lambda and just get the AA results directly.
|
|
auto AARGetter = [&](Function &F) -> AAResults & {
|
|
assert(&F == &OldF && "Called with an unexpected function!");
|
|
return FAM.getResult<AAManager>(F);
|
|
};
|
|
|
|
Function *NewF = promoteArguments(&OldF, AARGetter, MaxElements, None);
|
|
if (!NewF)
|
|
continue;
|
|
LocalChange = true;
|
|
|
|
// Directly substitute the functions in the call graph. Note that this
|
|
// requires the old function to be completely dead and completely
|
|
// replaced by the new function. It does no call graph updates, it merely
|
|
// swaps out the particular function mapped to a particular node in the
|
|
// graph.
|
|
C.getOuterRefSCC().replaceNodeFunction(N, *NewF);
|
|
OldF.eraseFromParent();
|
|
}
|
|
|
|
Changed |= LocalChange;
|
|
} while (LocalChange);
|
|
|
|
if (!Changed)
|
|
return PreservedAnalyses::all();
|
|
|
|
return PreservedAnalyses::none();
|
|
}
|
|
|
|
namespace {
|
|
|
|
/// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
|
|
struct ArgPromotion : public CallGraphSCCPass {
|
|
// Pass identification, replacement for typeid
|
|
static char ID;
|
|
|
|
explicit ArgPromotion(unsigned MaxElements = 3)
|
|
: CallGraphSCCPass(ID), MaxElements(MaxElements) {
|
|
initializeArgPromotionPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
void getAnalysisUsage(AnalysisUsage &AU) const override {
|
|
AU.addRequired<AssumptionCacheTracker>();
|
|
AU.addRequired<TargetLibraryInfoWrapperPass>();
|
|
getAAResultsAnalysisUsage(AU);
|
|
CallGraphSCCPass::getAnalysisUsage(AU);
|
|
}
|
|
|
|
bool runOnSCC(CallGraphSCC &SCC) override;
|
|
|
|
private:
|
|
using llvm::Pass::doInitialization;
|
|
|
|
bool doInitialization(CallGraph &CG) override;
|
|
|
|
/// The maximum number of elements to expand, or 0 for unlimited.
|
|
unsigned MaxElements;
|
|
};
|
|
|
|
} // end anonymous namespace
|
|
|
|
char ArgPromotion::ID = 0;
|
|
|
|
INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion",
|
|
"Promote 'by reference' arguments to scalars", false,
|
|
false)
|
|
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
|
|
INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
|
|
INITIALIZE_PASS_END(ArgPromotion, "argpromotion",
|
|
"Promote 'by reference' arguments to scalars", false, false)
|
|
|
|
Pass *llvm::createArgumentPromotionPass(unsigned MaxElements) {
|
|
return new ArgPromotion(MaxElements);
|
|
}
|
|
|
|
bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) {
|
|
if (skipSCC(SCC))
|
|
return false;
|
|
|
|
// Get the callgraph information that we need to update to reflect our
|
|
// changes.
|
|
CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
|
|
|
|
LegacyAARGetter AARGetter(*this);
|
|
|
|
bool Changed = false, LocalChange;
|
|
|
|
// Iterate until we stop promoting from this SCC.
|
|
do {
|
|
LocalChange = false;
|
|
// Attempt to promote arguments from all functions in this SCC.
|
|
for (CallGraphNode *OldNode : SCC) {
|
|
Function *OldF = OldNode->getFunction();
|
|
if (!OldF)
|
|
continue;
|
|
|
|
auto ReplaceCallSite = [&](CallSite OldCS, CallSite NewCS) {
|
|
Function *Caller = OldCS.getInstruction()->getParent()->getParent();
|
|
CallGraphNode *NewCalleeNode =
|
|
CG.getOrInsertFunction(NewCS.getCalledFunction());
|
|
CallGraphNode *CallerNode = CG[Caller];
|
|
CallerNode->replaceCallEdge(OldCS, NewCS, NewCalleeNode);
|
|
};
|
|
|
|
if (Function *NewF = promoteArguments(OldF, AARGetter, MaxElements,
|
|
{ReplaceCallSite})) {
|
|
LocalChange = true;
|
|
|
|
// Update the call graph for the newly promoted function.
|
|
CallGraphNode *NewNode = CG.getOrInsertFunction(NewF);
|
|
NewNode->stealCalledFunctionsFrom(OldNode);
|
|
if (OldNode->getNumReferences() == 0)
|
|
delete CG.removeFunctionFromModule(OldNode);
|
|
else
|
|
OldF->setLinkage(Function::ExternalLinkage);
|
|
|
|
// And updat ethe SCC we're iterating as well.
|
|
SCC.ReplaceNode(OldNode, NewNode);
|
|
}
|
|
}
|
|
// Remember that we changed something.
|
|
Changed |= LocalChange;
|
|
} while (LocalChange);
|
|
|
|
return Changed;
|
|
}
|
|
|
|
bool ArgPromotion::doInitialization(CallGraph &CG) {
|
|
return CallGraphSCCPass::doInitialization(CG);
|
|
}
|