// This file defines the ScalarEvolutionAliasAnalysis pass, which implements a
// simple alias analysis implemented in terms of ScalarEvolution queries.
//
+// This differs from traditional loop dependence analysis in that it tests
+// for dependencies within a single iteration of a loop, rather than
+// dependencies between different iterations.
+//
// ScalarEvolution has a more complete understanding of pointer arithmetic
// than BasicAliasAnalysis' collection of ad-hoc analyses.
//
//===----------------------------------------------------------------------===//
-#include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Analysis/ScalarEvolutionExpressions.h"
-#include "llvm/Analysis/Passes.h"
-#include "llvm/Pass.h"
+#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
using namespace llvm;
-namespace {
- /// ScalarEvolutionAliasAnalysis - This is a simple alias analysis
- /// implementation that uses ScalarEvolution to answer queries.
- class ScalarEvolutionAliasAnalysis : public FunctionPass,
- public AliasAnalysis {
- ScalarEvolution *SE;
-
- public:
- static char ID; // Class identification, replacement for typeinfo
- ScalarEvolutionAliasAnalysis() : FunctionPass(&ID), SE(0) {}
-
- private:
- virtual void getAnalysisUsage(AnalysisUsage &AU) const;
- virtual bool runOnFunction(Function &F);
- virtual AliasResult alias(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size);
-
- Value *GetUnderlyingIdentifiedObject(const SCEV *S);
- };
-} // End of anonymous namespace
-
-// Register this pass...
-char ScalarEvolutionAliasAnalysis::ID = 0;
-static RegisterPass<ScalarEvolutionAliasAnalysis>
-X("scev-aa", "ScalarEvolution-based Alias Analysis", false, true);
-
-// Declare that we implement the AliasAnalysis interface
-static RegisterAnalysisGroup<AliasAnalysis> Y(X);
-
-FunctionPass *llvm::createScalarEvolutionAliasAnalysisPass() {
- return new ScalarEvolutionAliasAnalysis();
-}
+AliasResult SCEVAAResult::alias(const MemoryLocation &LocA,
+ const MemoryLocation &LocB) {
+ // If either of the memory references is empty, it doesn't matter what the
+ // pointer values are. This allows the code below to ignore this special
+ // case.
+ if (LocA.Size == 0 || LocB.Size == 0)
+ return NoAlias;
-void
-ScalarEvolutionAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequiredTransitive<ScalarEvolution>();
- AU.setPreservesAll();
- AliasAnalysis::getAnalysisUsage(AU);
-}
+ // This is SCEVAAResult. Get the SCEVs!
+ const SCEV *AS = SE.getSCEV(const_cast<Value *>(LocA.Ptr));
+ const SCEV *BS = SE.getSCEV(const_cast<Value *>(LocB.Ptr));
-bool
-ScalarEvolutionAliasAnalysis::runOnFunction(Function &F) {
- InitializeAliasAnalysis(this);
- SE = &getAnalysis<ScalarEvolution>();
- return false;
+ // If they evaluate to the same expression, it's a MustAlias.
+ if (AS == BS)
+ return MustAlias;
+
+ // If something is known about the difference between the two addresses,
+ // see if it's enough to prove a NoAlias.
+ if (SE.getEffectiveSCEVType(AS->getType()) ==
+ SE.getEffectiveSCEVType(BS->getType())) {
+ unsigned BitWidth = SE.getTypeSizeInBits(AS->getType());
+ APInt ASizeInt(BitWidth, LocA.Size);
+ APInt BSizeInt(BitWidth, LocB.Size);
+
+ // Compute the difference between the two pointers.
+ const SCEV *BA = SE.getMinusSCEV(BS, AS);
+
+ // Test whether the difference is known to be great enough that memory of
+ // the given sizes don't overlap. This assumes that ASizeInt and BSizeInt
+ // are non-zero, which is special-cased above.
+ if (ASizeInt.ule(SE.getUnsignedRange(BA).getUnsignedMin()) &&
+ (-BSizeInt).uge(SE.getUnsignedRange(BA).getUnsignedMax()))
+ return NoAlias;
+
+ // Folding the subtraction while preserving range information can be tricky
+ // (because of INT_MIN, etc.); if the prior test failed, swap AS and BS
+ // and try again to see if things fold better that way.
+
+ // Compute the difference between the two pointers.
+ const SCEV *AB = SE.getMinusSCEV(AS, BS);
+
+ // Test whether the difference is known to be great enough that memory of
+ // the given sizes don't overlap. This assumes that ASizeInt and BSizeInt
+ // are non-zero, which is special-cased above.
+ if (BSizeInt.ule(SE.getUnsignedRange(AB).getUnsignedMin()) &&
+ (-ASizeInt).uge(SE.getUnsignedRange(AB).getUnsignedMax()))
+ return NoAlias;
+ }
+
+ // If ScalarEvolution can find an underlying object, form a new query.
+ // The correctness of this depends on ScalarEvolution not recognizing
+ // inttoptr and ptrtoint operators.
+ Value *AO = GetBaseValue(AS);
+ Value *BO = GetBaseValue(BS);
+ if ((AO && AO != LocA.Ptr) || (BO && BO != LocB.Ptr))
+ if (alias(MemoryLocation(AO ? AO : LocA.Ptr,
+ AO ? +MemoryLocation::UnknownSize : LocA.Size,
+ AO ? AAMDNodes() : LocA.AATags),
+ MemoryLocation(BO ? BO : LocB.Ptr,
+ BO ? +MemoryLocation::UnknownSize : LocB.Size,
+ BO ? AAMDNodes() : LocB.AATags)) == NoAlias)
+ return NoAlias;
+
+ // Forward the query to the next analysis.
+ return AAResultBase::alias(LocA, LocB);
}
-/// GetUnderlyingIdentifiedObject - Given an expression, try to find an
-/// "identified object" (see AliasAnalysis::isIdentifiedObject) base
-/// value. Return null is none was found.
-Value *
-ScalarEvolutionAliasAnalysis::GetUnderlyingIdentifiedObject(const SCEV *S) {
+/// Given an expression, try to find a base value.
+///
+/// Returns null if none was found.
+Value *SCEVAAResult::GetBaseValue(const SCEV *S) {
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
// In an addrec, assume that the base will be in the start, rather
// than the step.
- return GetUnderlyingIdentifiedObject(AR->getStart());
+ return GetBaseValue(AR->getStart());
} else if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(S)) {
// If there's a pointer operand, it'll be sorted at the end of the list.
- const SCEV *Last = A->getOperand(A->getNumOperands()-1);
- if (isa<PointerType>(Last->getType()))
- return GetUnderlyingIdentifiedObject(Last);
+ const SCEV *Last = A->getOperand(A->getNumOperands() - 1);
+ if (Last->getType()->isPointerTy())
+ return GetBaseValue(Last);
} else if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
- // Determine if we've found an Identified object.
- Value *V = U->getValue();
- if (isIdentifiedObject(V))
- return V;
+ // This is a leaf node.
+ return U->getValue();
}
// No Identified object found.
- return 0;
+ return nullptr;
}
-AliasAnalysis::AliasResult
-ScalarEvolutionAliasAnalysis::alias(const Value *A, unsigned ASize,
- const Value *B, unsigned BSize) {
- // This is ScalarEvolutionAliasAnalysis. Get the SCEVs!
- const SCEV *AS = SE->getSCEV(const_cast<Value *>(A));
- const SCEV *BS = SE->getSCEV(const_cast<Value *>(B));
+SCEVAAResult SCEVAA::run(Function &F, AnalysisManager<Function> *AM) {
+ return SCEVAAResult(AM->getResult<TargetLibraryAnalysis>(F),
+ AM->getResult<ScalarEvolutionAnalysis>(F));
+}
- // If they evaluate to the same expression, it's a MustAlias.
- if (AS == BS) return MustAlias;
+char SCEVAA::PassID;
- // If something is known about the difference between the two addresses,
- // see if it's enough to prove a NoAlias.
- if (SE->getEffectiveSCEVType(AS->getType()) ==
- SE->getEffectiveSCEVType(BS->getType())) {
- unsigned BitWidth = SE->getTypeSizeInBits(AS->getType());
- APInt AI(BitWidth, ASize);
- const SCEV *BA = SE->getMinusSCEV(BS, AS);
- if (AI.ule(SE->getUnsignedRange(BA).getUnsignedMin())) {
- APInt BI(BitWidth, BSize);
- const SCEV *AB = SE->getMinusSCEV(AS, BS);
- if (BI.ule(SE->getUnsignedRange(AB).getUnsignedMin()))
- return NoAlias;
- }
- }
+char SCEVAAWrapperPass::ID = 0;
+INITIALIZE_PASS_BEGIN(SCEVAAWrapperPass, "scev-aa",
+ "ScalarEvolution-based Alias Analysis", false, true)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_END(SCEVAAWrapperPass, "scev-aa",
+ "ScalarEvolution-based Alias Analysis", false, true)
- // If ScalarEvolution can find an underlying object, form a new query.
- // The correctness of this depends on ScalarEvolution not recognizing
- // inttoptr and ptrtoint operators.
- Value *AO = GetUnderlyingIdentifiedObject(AS);
- Value *BO = GetUnderlyingIdentifiedObject(BS);
- if ((AO && AO != A) || (BO && BO != B))
- if (alias(AO ? AO : A, AO ? ~0u : ASize,
- BO ? BO : B, BO ? ~0u : BSize) == NoAlias)
- return NoAlias;
+FunctionPass *llvm::createSCEVAAWrapperPass() {
+ return new SCEVAAWrapperPass();
+}
- // Forward the query to the next analysis.
- return AliasAnalysis::alias(A, ASize, B, BSize);
+SCEVAAWrapperPass::SCEVAAWrapperPass() : FunctionPass(ID) {
+ initializeSCEVAAWrapperPassPass(*PassRegistry::getPassRegistry());
+}
+
+bool SCEVAAWrapperPass::runOnFunction(Function &F) {
+ Result.reset(
+ new SCEVAAResult(getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
+ getAnalysis<ScalarEvolutionWrapperPass>().getSE()));
+ return false;
+}
+
+void SCEVAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesAll();
+ AU.addRequired<ScalarEvolutionWrapperPass>();
+ AU.addRequired<TargetLibraryInfoWrapperPass>();
}
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