[llvm] [AArch64][GlobalISel] Fold buildvector of bitcast (PR #141553)

[Amara Emerson via llvm-commits]

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@@ -386,6 +386,75 @@ void CombinerHelper::applyCombineConcatVectors(
   MI.eraseFromParent();
 }
 
+bool CombinerHelper::matchCombineBuildVectorOfBitcast(
+    MachineInstr &MI, SmallVector<Register> &Ops) const {
+  assert(MI.getOpcode() == TargetOpcode::G_BUILD_VECTOR &&
+         "Invalid instruction");
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aemerson wrote:

Can replace this with a `auto &BV = cast<GBuildVector>(MI);` which does an assertion for you. Then you have the `getNumSources()` and `getSourceReg(I)` helpers you can use later.

https://github.com/llvm/llvm-project/pull/141553