[llvm] [Transform][LoadStoreVectorizer] allow redundant in Chain (PR #163019)

[Drew Kersnar via llvm-commits]

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@@ -964,22 +977,24 @@ bool Vectorizer::vectorizeChain(Chain &C) {
 
     // Build the vector to store.
     Value *Vec = PoisonValue::get(VecTy);
-    unsigned VecIdx = 0;
-    auto InsertElem = [&](Value *V) {
+    auto InsertElem = [&](Value *V, unsigned VecIdx) {
       if (V->getType() != VecElemTy)
         V = Builder.CreateBitOrPointerCast(V, VecElemTy);
-      Vec = Builder.CreateInsertElement(Vec, V, Builder.getInt32(VecIdx++));
+      Vec = Builder.CreateInsertElement(Vec, V, Builder.getInt32(VecIdx));
     };
     for (const ChainElem &E : C) {
       auto *I = cast<StoreInst>(E.Inst);
+      int EOffset = (E.OffsetFromLeader - C[0].OffsetFromLeader).getSExtValue();
+      int VecIdx = 8 * EOffset / DL.getTypeSizeInBits(VecElemTy);
       if (FixedVectorType *VT =
               dyn_cast<FixedVectorType>(getLoadStoreType(I))) {
         for (int J = 0, JE = VT->getNumElements(); J < JE; ++J) {
           InsertElem(Builder.CreateExtractElement(I->getValueOperand(),
-                                                  Builder.getInt32(J)));
+                                                  Builder.getInt32(J)),
+                     VecIdx++);
         }
       } else {
-        InsertElem(I->getValueOperand());
+        InsertElem(I->getValueOperand(), VecIdx);
       }
     }
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dakersnar wrote:

Ahh, I see, makes sense. In that case, why change the store logic in vectorizeChain? Is it just to proactively account for potential future changes that allow these redundant stores to make it past splitChainByMayAliasInstrs? That sounds reasonable to me if so.

https://github.com/llvm/llvm-project/pull/163019