[llvm] AMDGPU/GlobalISel: add RegBankLegalize rules for bitfield extract (PR #132381)

[Pierre van Houtryve via llvm-commits]

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@@ -127,6 +131,112 @@ void RegBankLegalizeHelper::widenLoad(MachineInstr &MI, LLT WideTy,
   MI.eraseFromParent();
 }
 
+static bool isSignedBFE(MachineInstr &MI) {
+  if (isa<GIntrinsic>(MI)) {
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Pierre-vh wrote:

nit: How about dyn_cast + use the `.is(IID)` helper?

https://github.com/llvm/llvm-project/pull/132381