[llvm] [InstCombine] Handle more scalable geps in EmitGEPOffset (PR #71699)

[Nikita Popov via llvm-commits]

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@@ -66,16 +66,26 @@ Value *llvm::emitGEPOffset(IRBuilderBase *Builder, const DataLayout &DL,
     // Splat the index if needed.
     if (IntIdxTy->isVectorTy() && !Op->getType()->isVectorTy())
       Op = Builder->CreateVectorSplat(
-          cast<FixedVectorType>(IntIdxTy)->getNumElements(), Op);
+          cast<VectorType>(IntIdxTy)->getElementCount(), Op);
 
     // Convert to correct type.
     if (Op->getType() != IntIdxTy)
       Op = Builder->CreateIntCast(Op, IntIdxTy, true, Op->getName() + ".c");
     if (Size != 1 || TSize.isScalable()) {
       // We'll let instcombine(mul) convert this to a shl if possible.
-      auto *ScaleC = ConstantInt::get(IntIdxTy, Size);
-      Value *Scale =
-          !TSize.isScalable() ? ScaleC : Builder->CreateVScale(ScaleC);
+      Value *Scale = ConstantInt::get(IntIdxTy, Size);
+      if (TSize.isScalable()) {
+        Value *VScale;
+        if (IntIdxTy->isVectorTy()) {
+          VScale = Builder->CreateVScale(ConstantInt::get(
+              cast<VectorType>(IntIdxTy)->getElementType(), 1));
+          VScale = Builder->CreateVectorSplat(
+              cast<VectorType>(IntIdxTy)->getElementCount(), VScale);
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nikic wrote:

Can we instead move the above splat creation until after the multiply? I.e. calculate on scalars and then splat?

https://github.com/llvm/llvm-project/pull/71699