[llvm] [InstCombine] Remove scalable vector extracts to and from the same type (PR #69702)

[David Sherwood via llvm-commits]

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@@ -2997,24 +2997,26 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
         return replaceOperand(CI, 0, InsertTuple);
     }
 
-    auto *DstTy = dyn_cast<FixedVectorType>(ReturnType);
-    auto *VecTy = dyn_cast<FixedVectorType>(Vec->getType());
+    auto *DstTy = dyn_cast<VectorType>(ReturnType);
+    auto *VecTy = dyn_cast<VectorType>(Vec->getType());
 
-    // Only canonicalize if the destination vector and Vec are fixed
-    // vectors.
     if (DstTy && VecTy) {
-      unsigned DstNumElts = DstTy->getNumElements();
-      unsigned VecNumElts = VecTy->getNumElements();
+      auto DstEltCnt = DstTy->getElementCount();
       unsigned IdxN = cast<ConstantInt>(Idx)->getZExtValue();
 
       // Extracting the entirety of Vec is a nop.
-      if (VecNumElts == DstNumElts) {
+      if (DstEltCnt == VecTy->getElementCount()) {
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david-arm wrote:

nit: Given you have to query the element count for VecTy anyway here you could just save a copy of it, i.e.

`auto VecEltCnt = VecTy->getElementCount();`

and reuse it for the check below so it's consistent with  Dst, i.e.

`if (VecEltCnt.isScalable() || DstEltCnt.isScalable())`

https://github.com/llvm/llvm-project/pull/69702