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