[llvm] [AArch64][GlobalISel] Legalize Insert vector element (PR #81453)

[Matt Arsenault via llvm-commits]

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@@ -2972,7 +2972,22 @@ bool IRTranslator::translateInsertElement(const User &U,
   Register Res = getOrCreateVReg(U);
   Register Val = getOrCreateVReg(*U.getOperand(0));
   Register Elt = getOrCreateVReg(*U.getOperand(1));
-  Register Idx = getOrCreateVReg(*U.getOperand(2));
+  const auto &TLI = *MF->getSubtarget().getTargetLowering();
+  unsigned PreferredVecIdxWidth = TLI.getVectorIdxTy(*DL).getSizeInBits();
+  Register Idx;
+  if (auto *CI = dyn_cast<ConstantInt>(U.getOperand(2))) {
+    if (CI->getBitWidth() != PreferredVecIdxWidth) {
+      APInt NewIdx = CI->getValue().zextOrTrunc(PreferredVecIdxWidth);
+      auto *NewIdxCI = ConstantInt::get(CI->getContext(), NewIdx);
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arsenm wrote:

Then that's also wrong. This is doing legalization work in the IRTranslator 

https://github.com/llvm/llvm-project/pull/81453