1 files changed, 169 insertions, 0 deletions
diff --git a/contrib/llvm-project/llvm/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp b/contrib/llvm-project/llvm/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp
new file mode 100644
index 000000000000..af8232b03f1e
--- /dev/null
+++ b/contrib/llvm-project/llvm/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp
@@ -0,0 +1,169 @@
+//===- ScalarEvolutionAliasAnalysis.cpp - SCEV-based Alias Analysis -------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// 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"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/InitializePasses.h"
+using namespace llvm;
+
+static bool canComputePointerDiff(ScalarEvolution &SE,
+                                  const SCEV *A, const SCEV *B) {
+  if (SE.getEffectiveSCEVType(A->getType()) !=
+      SE.getEffectiveSCEVType(B->getType()))
+    return false;
+
+  return SE.instructionCouldExistWithOperands(A, B);
+}
+
+AliasResult SCEVAAResult::alias(const MemoryLocation &LocA,
+                                const MemoryLocation &LocB, AAQueryInfo &AAQI,
+                                const Instruction *) {
+  // 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.isZero() || LocB.Size.isZero())
+    return AliasResult::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 AliasResult::MustAlias;
+
+  // If something is known about the difference between the two addresses,
+  // see if it's enough to prove a NoAlias.
+  if (canComputePointerDiff(SE, AS, BS)) {
+    unsigned BitWidth = SE.getTypeSizeInBits(AS->getType());
+    APInt ASizeInt(BitWidth, LocA.Size.hasValue()
+                                 ? static_cast<uint64_t>(LocA.Size.getValue())
+                                 : MemoryLocation::UnknownSize);
+    APInt BSizeInt(BitWidth, LocB.Size.hasValue()
+                                 ? static_cast<uint64_t>(LocB.Size.getValue())
+                                 : MemoryLocation::UnknownSize);
+
+    // 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 (!isa<SCEVCouldNotCompute>(BA) &&
+        ASizeInt.ule(SE.getUnsignedRange(BA).getUnsignedMin()) &&
+        (-BSizeInt).uge(SE.getUnsignedRange(BA).getUnsignedMax()))
+      return AliasResult::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 (!isa<SCEVCouldNotCompute>(AB) &&
+        BSizeInt.ule(SE.getUnsignedRange(AB).getUnsignedMin()) &&
+        (-ASizeInt).uge(SE.getUnsignedRange(AB).getUnsignedMax()))
+      return AliasResult::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 ? LocationSize::beforeOrAfterPointer()
+                                : LocA.Size,
+                             AO ? AAMDNodes() : LocA.AATags),
+              MemoryLocation(BO ? BO : LocB.Ptr,
+                             BO ? LocationSize::beforeOrAfterPointer()
+                                : LocB.Size,
+                             BO ? AAMDNodes() : LocB.AATags),
+              AAQI, nullptr) == AliasResult::NoAlias)
+      return AliasResult::NoAlias;
+
+  return AliasResult::MayAlias;
+}
+
+/// 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;
+}
+
+bool SCEVAAResult::invalidate(Function &Fn, const PreservedAnalyses &PA,
+                              FunctionAnalysisManager::Invalidator &Inv) {
+  // We don't care if this analysis itself is preserved, it has no state. But
+  // we need to check that the analyses it depends on have been.
+  return Inv.invalidate<ScalarEvolutionAnalysis>(Fn, PA);
+}
+
+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>();
+}