Check in LLVM r95781.
diff --git a/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp b/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp
new file mode 100644
index 0000000..498c4a8
--- /dev/null
+++ b/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp
@@ -0,0 +1,139 @@
+//===- ScalarEvolutionAliasAnalysis.cpp - SCEV-based Alias Analysis -------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the ScalarEvolutionAliasAnalysis pass, which implements a
+// simple alias analysis implemented in terms of ScalarEvolution queries.
+//
+// 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"
+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) {}
+
+ /// getAdjustedAnalysisPointer - This method is used when a pass implements
+ /// an analysis interface through multiple inheritance. If needed, it
+ /// should override this to adjust the this pointer as needed for the
+ /// specified pass info.
+ virtual void *getAdjustedAnalysisPointer(const PassInfo *PI) {
+ if (PI->isPassID(&AliasAnalysis::ID))
+ return (AliasAnalysis*)this;
+ return this;
+ }
+
+ 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 *GetBaseValue(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();
+}
+
+void
+ScalarEvolutionAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequiredTransitive<ScalarEvolution>();
+ AU.setPreservesAll();
+ AliasAnalysis::getAnalysisUsage(AU);
+}
+
+bool
+ScalarEvolutionAliasAnalysis::runOnFunction(Function &F) {
+ InitializeAliasAnalysis(this);
+ SE = &getAnalysis<ScalarEvolution>();
+ return false;
+}
+
+/// 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)) {
+ // 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 GetBaseValue(Last);
+ } else if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
+ // This is a leaf node.
+ return U->getValue();
+ }
+ // No Identified object found.
+ return 0;
+}
+
+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));
+
+ // 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 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;
+ }
+ }
+
+ // 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 != A) || (BO && BO != B))
+ if (alias(AO ? AO : A, AO ? ~0u : ASize,
+ BO ? BO : B, BO ? ~0u : BSize) == NoAlias)
+ return NoAlias;
+
+ // Forward the query to the next analysis.
+ return AliasAnalysis::alias(A, ASize, B, BSize);
+}