142 lines
5.4 KiB
C++
142 lines
5.4 KiB
C++
//===- LibCallAliasAnalysis.cpp - Implement AliasAnalysis for libcalls ----===//
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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 file implements the LibCallAliasAnalysis class.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/LibCallAliasAnalysis.h"
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#include "llvm/Analysis/LibCallSemantics.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/IR/Function.h"
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#include "llvm/Pass.h"
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using namespace llvm;
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// Register this pass...
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char LibCallAliasAnalysis::ID = 0;
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INITIALIZE_AG_PASS(LibCallAliasAnalysis, AliasAnalysis, "libcall-aa",
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"LibCall Alias Analysis", false, true, false)
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FunctionPass *llvm::createLibCallAliasAnalysisPass(LibCallInfo *LCI) {
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return new LibCallAliasAnalysis(LCI);
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}
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LibCallAliasAnalysis::~LibCallAliasAnalysis() {
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delete LCI;
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}
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void LibCallAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
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AliasAnalysis::getAnalysisUsage(AU);
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AU.setPreservesAll(); // Does not transform code
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}
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bool LibCallAliasAnalysis::runOnFunction(Function &F) {
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// set up super class
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InitializeAliasAnalysis(this, &F.getParent()->getDataLayout());
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return false;
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}
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/// AnalyzeLibCallDetails - Given a call to a function with the specified
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/// LibCallFunctionInfo, see if we can improve the mod/ref footprint of the call
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/// vs the specified pointer/size.
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AliasAnalysis::ModRefResult
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LibCallAliasAnalysis::AnalyzeLibCallDetails(const LibCallFunctionInfo *FI,
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ImmutableCallSite CS,
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const MemoryLocation &Loc) {
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// If we have a function, check to see what kind of mod/ref effects it
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// has. Start by including any info globally known about the function.
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AliasAnalysis::ModRefResult MRInfo = FI->UniversalBehavior;
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if (MRInfo == NoModRef) return MRInfo;
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// If that didn't tell us that the function is 'readnone', check to see
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// if we have detailed info and if 'P' is any of the locations we know
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// about.
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const LibCallFunctionInfo::LocationMRInfo *Details = FI->LocationDetails;
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if (Details == nullptr)
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return MRInfo;
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// If the details array is of the 'DoesNot' kind, we only know something if
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// the pointer is a match for one of the locations in 'Details'. If we find a
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// match, we can prove some interactions cannot happen.
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//
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if (FI->DetailsType == LibCallFunctionInfo::DoesNot) {
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// Find out if the pointer refers to a known location.
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for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
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const LibCallLocationInfo &LocInfo =
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LCI->getLocationInfo(Details[i].LocationID);
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LibCallLocationInfo::LocResult Res = LocInfo.isLocation(CS, Loc);
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if (Res != LibCallLocationInfo::Yes) continue;
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// If we find a match against a location that we 'do not' interact with,
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// learn this info into MRInfo.
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return ModRefResult(MRInfo & ~Details[i].MRInfo);
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}
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return MRInfo;
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}
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// If the details are of the 'DoesOnly' sort, we know something if the pointer
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// is a match for one of the locations in 'Details'. Also, if we can prove
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// that the pointers is *not* one of the locations in 'Details', we know that
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// the call is NoModRef.
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assert(FI->DetailsType == LibCallFunctionInfo::DoesOnly);
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// Find out if the pointer refers to a known location.
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bool NoneMatch = true;
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for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
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const LibCallLocationInfo &LocInfo =
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LCI->getLocationInfo(Details[i].LocationID);
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LibCallLocationInfo::LocResult Res = LocInfo.isLocation(CS, Loc);
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if (Res == LibCallLocationInfo::No) continue;
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// If we don't know if this pointer points to the location, then we have to
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// assume it might alias in some case.
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if (Res == LibCallLocationInfo::Unknown) {
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NoneMatch = false;
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continue;
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}
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// If we know that this pointer definitely is pointing into the location,
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// merge in this information.
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return ModRefResult(MRInfo & Details[i].MRInfo);
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}
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// If we found that the pointer is guaranteed to not match any of the
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// locations in our 'DoesOnly' rule, then we know that the pointer must point
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// to some other location. Since the libcall doesn't mod/ref any other
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// locations, return NoModRef.
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if (NoneMatch)
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return NoModRef;
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// Otherwise, return any other info gained so far.
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return MRInfo;
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}
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// getModRefInfo - Check to see if the specified callsite can clobber the
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// specified memory object.
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//
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AliasAnalysis::ModRefResult
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LibCallAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
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const MemoryLocation &Loc) {
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ModRefResult MRInfo = ModRef;
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// If this is a direct call to a function that LCI knows about, get the
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// information about the runtime function.
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if (LCI) {
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if (const Function *F = CS.getCalledFunction()) {
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if (const LibCallFunctionInfo *FI = LCI->getFunctionInfo(F)) {
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MRInfo = ModRefResult(MRInfo & AnalyzeLibCallDetails(FI, CS, Loc));
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if (MRInfo == NoModRef) return NoModRef;
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}
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}
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}
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// The AliasAnalysis base class has some smarts, lets use them.
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return (ModRefResult)(MRInfo | AliasAnalysis::getModRefInfo(CS, Loc));
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}
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