[llvm] [SLP][REVEC] Expand getelementptr into vector form. (PR #103704)

[Han-Kuan Chen via llvm-commits]

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@@ -13760,6 +13760,26 @@ Value *BoUpSLP::vectorizeTree(TreeEntry *E, bool PostponedPHIs) {
           LLVM_DEBUG(dbgs() << "SLP: Diamond merged for " << *VL0 << ".\n");
           return E->VectorizedValue;
         }
+        if (isa<FixedVectorType>(ScalarTy)) {
+          assert(SLPReVec && "FixedVectorType is not expected.");
+          // CreateMaskedGather expects VecTy and VecPtr have same size. We need
+          // to expand VecPtr if ScalarTy is a vector type.
+          unsigned ScalarTyNumElements =
+              cast<FixedVectorType>(ScalarTy)->getNumElements();
+          unsigned VecTyNumElements =
+              cast<FixedVectorType>(VecTy)->getNumElements();
+          SmallVector<Constant *> Indices(VecTyNumElements);
+          transform(seq(VecTyNumElements), Indices.begin(), [=](unsigned I) {
+            return Builder.getInt64(I % ScalarTyNumElements);
+          });
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HanKuanChen wrote:

> Also, do you have the cost model for this change?

GEPs are calculated by `TTI.getGEPCost` in `getGEPCosts`.
`TTI->getGatherScatterOpCost` correctly calculates the cost if ScalarTy is FixedVectorType.

https://github.com/llvm/llvm-project/pull/103704