[Loads] Move generic code out of vectorizer into a location it might be reused [NFC]

llvm-svn: 371558

1 files changed, 50 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp
index e74df9c69d7..ea98ca915c6 100644
--- a/llvm/lib/Analysis/Loads.cpp
+++ b/llvm/lib/Analysis/Loads.cpp
@@ -12,6 +12,9 @@
 
 #include "llvm/Analysis/Loads.h"
 #include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/GlobalAlias.h"
@@ -190,6 +193,53 @@ static bool AreEquivalentAddressValues(const Value *A, const Value *B) {
   return false;
 }
 
+bool llvm::isDereferenceableAndAlignedInLoop(LoadInst *LI, Loop *L,
+                                             ScalarEvolution &SE,
+                                             DominatorTree &DT) {
+  auto &DL = LI->getModule()->getDataLayout();
+  Value *Ptr = LI->getPointerOperand();
+  auto *AddRec = dyn_cast<SCEVAddRecExpr>(SE.getSCEV(Ptr));
+  if (!AddRec || AddRec->getLoop() != L || !AddRec->isAffine())
+    return false;
+  auto* Step = dyn_cast<SCEVConstant>(AddRec->getStepRecurrence(SE));
+  if (!Step)
+    return false;
+  APInt StepC = Step->getAPInt();
+  APInt EltSize(DL.getIndexTypeSizeInBits(Ptr->getType()),
+                 DL.getTypeStoreSize(LI->getType()));
+  // TODO: generalize to access patterns which have gaps
+  // TODO: handle uniform addresses (if not already handled by LICM)
+  if (StepC != EltSize)
+    return false;
+
+  // TODO: If the symbolic trip count has a small bound (max count), we might
+  // be able to prove safety.
+  auto TC = SE.getSmallConstantTripCount(L);
+  if (!TC)
+    return false;
+
+  const APInt AccessSize = TC * EltSize;
+
+  auto *StartS = dyn_cast<SCEVUnknown>(AddRec->getStart());
+  if (!StartS)
+    return false;
+  assert(SE.isLoopInvariant(StartS, L) && "implied by addrec definition");
+  Value *Base = StartS->getValue();
+
+  Instruction *HeaderFirstNonPHI = L->getHeader()->getFirstNonPHI();
+
+  unsigned Align = LI->getAlignment();
+  if (Align == 0)
+    Align = DL.getABITypeAlignment(LI->getType());
+  // For the moment, restrict ourselves to the case where the access size is a
+  // multiple of the requested alignment and the base is aligned.
+  // TODO: generalize if a case found which warrants
+  if (EltSize.urem(Align) != 0)
+    return false;
+  return isDereferenceableAndAlignedPointer(Base, Align, AccessSize,
+                                            DL, HeaderFirstNonPHI, &DT);
+}
+
 /// Check if executing a load of this pointer value cannot trap.
 ///
 /// If DT and ScanFrom are specified this method performs context-sensitive