Don't use PassInfo* as a type identifier for passes. Instead, use the address of...

[oota-llvm.git] / lib / Analysis / ScalarEvolutionAliasAnalysis.cpp

diff --git a/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp b/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp
index ef0e97b6e10ebdc4a4562b6c27af58442ad5268d..93b2a8b06fbe9a8a8d8df7ff3a02ffb28e9f85c5 100644 (file)
--- a/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp
+++ b/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp
@@ -10,6 +10,10 @@
 // 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.
 //
@@ -30,7 +34,17 @@ namespace {
 
   public:
     static char ID; // Class identification, replacement for typeinfo
-    ScalarEvolutionAliasAnalysis() : FunctionPass(&ID), SE(0) {}
+    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(AnalysisID PI) {
+      if (PI == &AliasAnalysis::ID)
+        return (AliasAnalysis*)this;
+      return this;
+    }
 
   private:
     virtual void getAnalysisUsage(AnalysisUsage &AU) const;
@@ -44,11 +58,8 @@ 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(ScalarEvolutionAliasAnalysis, AliasAnalysis, "scev-aa",
+                   "ScalarEvolution-based Alias Analysis", false, true, false);
 
 FunctionPass *llvm::createScalarEvolutionAliasAnalysisPass() {
   return new ScalarEvolutionAliasAnalysis();
@@ -79,7 +90,7 @@ ScalarEvolutionAliasAnalysis::GetBaseValue(const SCEV *S) {
   } 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()))
+    if (Last->getType()->isPointerTy())
       return GetBaseValue(Last);
   } else if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
     // This is a leaf node.
@@ -92,6 +103,12 @@ ScalarEvolutionAliasAnalysis::GetBaseValue(const SCEV *S) {
 AliasAnalysis::AliasResult
 ScalarEvolutionAliasAnalysis::alias(const Value *A, unsigned ASize,
                                     const Value *B, unsigned BSize) {
+  // 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 (ASize == 0 || BSize == 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));
@@ -104,14 +121,32 @@ ScalarEvolutionAliasAnalysis::alias(const Value *A, unsigned ASize,
   if (SE->getEffectiveSCEVType(AS->getType()) ==
       SE->getEffectiveSCEVType(BS->getType())) {
     unsigned BitWidth = SE->getTypeSizeInBits(AS->getType());
-    APInt AI(BitWidth, ASize);
+    APInt ASizeInt(BitWidth, ASize);
+    APInt BSizeInt(BitWidth, BSize);
+
+    // 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.
@@ -120,8 +155,8 @@ ScalarEvolutionAliasAnalysis::alias(const Value *A, unsigned ASize,
   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)
+    if (alias(AO ? AO : A, AO ? UnknownSize : ASize,
+              BO ? BO : B, BO ? UnknownSize : BSize) == NoAlias)
       return NoAlias;
 
   // Forward the query to the next analysis.