// 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/Support/Compiler.h"
+#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
using namespace llvm;
-namespace {
- /// ScalarEvolutionAliasAnalysis - This is a simple alias analysis
- /// implementation that uses ScalarEvolution to answer queries.
- class VISIBILITY_HIDDEN 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);
+INITIALIZE_AG_PASS_BEGIN(ScalarEvolutionAliasAnalysis, AliasAnalysis, "scev-aa",
+ "ScalarEvolution-based Alias Analysis", false, true,
+ false)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
+INITIALIZE_AG_PASS_END(ScalarEvolutionAliasAnalysis, AliasAnalysis, "scev-aa",
+ "ScalarEvolution-based Alias Analysis", false, true,
+ false)
FunctionPass *llvm::createScalarEvolutionAliasAnalysisPass() {
return new ScalarEvolutionAliasAnalysis();
}
-void
-ScalarEvolutionAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
+void ScalarEvolutionAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredTransitive<ScalarEvolution>();
AU.setPreservesAll();
AliasAnalysis::getAnalysisUsage(AU);
}
-bool
-ScalarEvolutionAliasAnalysis::runOnFunction(Function &F) {
- InitializeAliasAnalysis(this);
+bool ScalarEvolutionAliasAnalysis::runOnFunction(Function &F) {
+ InitializeAliasAnalysis(this, &F.getParent()->getDataLayout());
SE = &getAnalysis<ScalarEvolution>();
return false;
}
-Value *
-ScalarEvolutionAliasAnalysis::GetUnderlyingIdentifiedObject(const SCEV *S) {
+/// GetBaseValue - Given an expression, try to find a
+/// base value. Return null is none was found.
+Value *ScalarEvolutionAliasAnalysis::GetBaseValue(const SCEV *S) {
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
- return GetUnderlyingIdentifiedObject(AR->getStart());
+ // In an addrec, assume that the base will be in the start, rather
+ // than the step.
+ 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) {
+AliasResult ScalarEvolutionAliasAnalysis::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;
+
// This is ScalarEvolutionAliasAnalysis. Get the SCEVs!
- const SCEV *AS = SE->getSCEV(const_cast<Value *>(A));
- const SCEV *BS = SE->getSCEV(const_cast<Value *>(B));
+ const SCEV *AS = SE->getSCEV(const_cast<Value *>(LocA.Ptr));
+ const SCEV *BS = SE->getSCEV(const_cast<Value *>(LocB.Ptr));
// If they evaluate to the same expression, it's a MustAlias.
- if (AS == BS) return 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 AI(BitWidth, ASize);
+ APInt ASizeInt(BitWidth, LocA.Size);
+ APInt BSizeInt(BitWidth, LocB.Size);
+
+ // Compute the difference between the two pointers.
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;
- }
+
+ // 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 = 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)
+ 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 AliasAnalysis::alias(A, ASize, B, BSize);
+ return AliasAnalysis::alias(LocA, LocB);
}
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