[llvm] [LLVM] Add `llvm.masked.compress` intrinsic (PR #92289)

[Matt Arsenault via llvm-commits]

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@@ -7502,6 +7504,53 @@ LegalizerHelper::lowerShuffleVector(MachineInstr &MI) {
   return Legalized;
 }
 
+LegalizerHelper::LegalizeResult
+LegalizerHelper::lowerMCOMPRESS(llvm::MachineInstr &MI) {
+  auto [Dst, DstTy, Vec, VecTy, Mask, MaskTy] = MI.getFirst3RegLLTs();
+
+  if (VecTy.isScalableVector())
+    report_fatal_error(
+        "Lowering masked_compress for scalable vectors is undefined.");
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arsenm wrote:

I'd expect this to be caught in the IR verifier, and then you don't need to worry about it 

https://github.com/llvm/llvm-project/pull/92289