[LoadStoreVectorizer] Use getMinusScev() to compute the distance between two pointers.

Summary: Currently, isConsecutiveAccess() detects two pointers(PtrA and PtrB) as consecutive by
         comparing PtrB with BaseDelta+PtrA. This works when both pointers are factorized or
         both of them are not factorized. But isConsecutiveAccess() fails if one of the
         pointers is factorized but the other one is not.

         Here is an example:
         PtrA = 4 * (A + B)
         PtrB = 4 + 4A + 4B

         This patch uses getMinusSCEV() to compute the distance between two pointers.
         getMinusSCEV() allows combining the expressions and computing the simplified distance.

Author: FarhanaAleen

Reviewed By: rampitec

Differential Revision: https://reviews.llvm.org/D49516

llvm-svn: 337471

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp b/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
index ce77ea80a28..8ce408294c0 100644
--- a/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
@@ -340,6 +340,14 @@ bool Vectorizer::isConsecutiveAccess(Value *A, Value *B) {
   if (X == PtrSCEVB)
     return true;
 
+  // The above check will not catch the cases where one of the pointers is
+  // factorized but the other one is not, such as (C + (S * (A + B))) vs
+  // (AS + BS). Get the minus scev. That will allow re-combining the expresions
+  // and getting the simplified difference.
+  const SCEV *Dist = SE.getMinusSCEV(PtrSCEVB, PtrSCEVA);
+  if (C == Dist)
+    return true;
+
   // Sometimes even this doesn't work, because SCEV can't always see through
   // patterns that look like (gep (ext (add (shl X, C1), C2))). Try checking
   // things the hard way.