Imported Upstream version 6.0.0.172

Former-commit-id: f3cc9b82f3e5bd8f0fd3ebc098f789556b44e9cd

external/llvm/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp

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+//===- 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.
+//
+// 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/ScalarEvolutionAliasAnalysis.h"
+using namespace llvm;
+
+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;
+
+  // 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));
+
+  // 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);
+}
+
+/// 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 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 (Last->getType()->isPointerTy())
+      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 nullptr;
+}
+
+AnalysisKey SCEVAA::Key;
+
+SCEVAAResult SCEVAA::run(Function &F, FunctionAnalysisManager &AM) {
+  return SCEVAAResult(AM.getResult<ScalarEvolutionAnalysis>(F));
+}
+
+char SCEVAAWrapperPass::ID = 0;
+INITIALIZE_PASS_BEGIN(SCEVAAWrapperPass, "scev-aa",
+                      "ScalarEvolution-based Alias Analysis", false, true)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
+INITIALIZE_PASS_END(SCEVAAWrapperPass, "scev-aa",
+                    "ScalarEvolution-based Alias Analysis", false, true)
+
+FunctionPass *llvm::createSCEVAAWrapperPass() {
+  return new SCEVAAWrapperPass();
+}
+
+SCEVAAWrapperPass::SCEVAAWrapperPass() : FunctionPass(ID) {
+  initializeSCEVAAWrapperPassPass(*PassRegistry::getPassRegistry());
+}
+
+bool SCEVAAWrapperPass::runOnFunction(Function &F) {
+  Result.reset(
+      new SCEVAAResult(getAnalysis<ScalarEvolutionWrapperPass>().getSE()));
+  return false;
+}
+
+void SCEVAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.setPreservesAll();
+  AU.addRequired<ScalarEvolutionWrapperPass>();
+}