[llvm] Re-land [Transform][LoadStoreVectorizer] allow redundant in Chain (PR #168135)

[Drew Kersnar via llvm-commits]

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@@ -626,22 +626,25 @@ std::vector<Chain> Vectorizer::splitChainByContiguity(Chain &C) {
   std::vector<Chain> Ret;
   Ret.push_back({C.front()});
 
-  unsigned ElemBytes = DL.getTypeStoreSize(getChainElemTy(C));
+  unsigned ChainElemTyBits = DL.getTypeSizeInBits(getChainElemTy(C));
   APInt PrevReadEnd = C[0].OffsetFromLeader +
                       DL.getTypeStoreSize(getLoadStoreType(&*C[0].Inst));
   for (auto It = std::next(C.begin()), End = C.end(); It != End; ++It) {
-    // `prev` accesses offsets [PrevDistFromBase, PrevReadEnd).
     auto &CurChain = Ret.back();
     unsigned SzBytes = DL.getTypeStoreSize(getLoadStoreType(&*It->Inst));
 
     // Add this instruction to the end of the current chain, or start a new one.
-    assert(SzBytes % ElemBytes == 0);
+    assert(
+        8 * SzBytes % ChainElemTyBits == 0 &&
+        "Every chain-element size must be a multiple of the element size after "
+        "vectorization.");
     APInt ReadEnd = It->OffsetFromLeader + SzBytes;
     // Allow redundancy: partial or full overlap counts as contiguous.
     bool AreContiguous = false;
     if (It->OffsetFromLeader.sle(PrevReadEnd)) {
+      // Check overlap is a multiple of the element size after vectorization.
       uint64_t Overlap = (PrevReadEnd - It->OffsetFromLeader).getZExtValue();
-      if (Overlap % ElemBytes == 0)
+      if (8 * Overlap % ChainElemTyBits == 0)
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dakersnar wrote:

Will this overlap condition ever fail? If so, can you add a unit test that demonstrates an example where the chain is broken due to this condition being false? And if not, maybe we should change this to an assert.

https://github.com/llvm/llvm-project/pull/168135