forked from OSchip/llvm-project
130 lines
5.0 KiB
C++
130 lines
5.0 KiB
C++
//===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source 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 generic AliasAnalysis interface which is used as the
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// common interface used by all clients and implementations of alias analysis.
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//
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// This file also implements the default version of the AliasAnalysis interface
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// that is to be used when no other implementation is specified. This does some
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// simple tests that detect obvious cases: two different global pointers cannot
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// alias, a global cannot alias a malloc, two different mallocs cannot alias,
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// etc.
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//
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// This alias analysis implementation really isn't very good for anything, but
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// it is very fast, and makes a nice clean default implementation. Because it
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// handles lots of little corner cases, other, more complex, alias analysis
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// implementations may choose to rely on this pass to resolve these simple and
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// easy cases.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/iMemory.h"
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#include "llvm/Target/TargetData.h"
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namespace llvm {
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// Register the AliasAnalysis interface, providing a nice name to refer to.
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namespace {
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RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) {
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return alias(L->getOperand(0), TD->getTypeSize(L->getType()),
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P, Size) ? Ref : NoModRef;
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(StoreInst *S, Value *P, unsigned Size) {
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return alias(S->getOperand(1), TD->getTypeSize(S->getOperand(0)->getType()),
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P, Size) ? Mod : NoModRef;
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}
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// AliasAnalysis destructor: DO NOT move this to the header file for
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// AliasAnalysis or else clients of the AliasAnalysis class may not depend on
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// the AliasAnalysis.o file in the current .a file, causing alias analysis
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// support to not be included in the tool correctly!
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//
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AliasAnalysis::~AliasAnalysis() {}
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/// setTargetData - Subclasses must call this method to initialize the
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/// AliasAnalysis interface before any other methods are called.
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///
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void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
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TD = &P->getAnalysis<TargetData>();
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}
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// getAnalysisUsage - All alias analysis implementations should invoke this
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// directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that
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// TargetData is required by the pass.
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void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<TargetData>(); // All AA's need TargetData.
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}
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/// canBasicBlockModify - Return true if it is possible for execution of the
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/// specified basic block to modify the value pointed to by Ptr.
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///
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bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
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const Value *Ptr, unsigned Size) {
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return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size);
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}
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/// canInstructionRangeModify - Return true if it is possible for the execution
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/// of the specified instructions to modify the value pointed to by Ptr. The
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/// instructions to consider are all of the instructions in the range of [I1,I2]
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/// INCLUSIVE. I1 and I2 must be in the same basic block.
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///
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bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
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const Instruction &I2,
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const Value *Ptr, unsigned Size) {
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assert(I1.getParent() == I2.getParent() &&
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"Instructions not in same basic block!");
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BasicBlock::iterator I = const_cast<Instruction*>(&I1);
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BasicBlock::iterator E = const_cast<Instruction*>(&I2);
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++E; // Convert from inclusive to exclusive range.
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for (; I != E; ++I) // Check every instruction in range
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if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod)
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return true;
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return false;
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}
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// Because of the way .a files work, we must force the BasicAA implementation to
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// be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run
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// the risk of AliasAnalysis being used, but the default implementation not
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// being linked into the tool that uses it.
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//
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extern void BasicAAStub();
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static IncludeFile INCLUDE_BASICAA_CPP((void*)&BasicAAStub);
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namespace {
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struct NoAA : public ImmutablePass, public AliasAnalysis {
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AliasAnalysis::getAnalysisUsage(AU);
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}
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virtual void initializePass() {
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InitializeAliasAnalysis(this);
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}
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};
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// Register this pass...
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RegisterOpt<NoAA>
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X("no-aa", "No Alias Analysis (always returns 'may' alias)");
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// Declare that we implement the AliasAnalysis interface
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RegisterAnalysisGroup<AliasAnalysis, NoAA> Y;
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} // End of anonymous namespace
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} // End llvm namespace
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