[llvm] [RISCV][GISEL] Legalize G_EXTRACT_SUBVECTOR (PR #109426)

[Craig Topper via llvm-commits]

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@@ -597,6 +597,24 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
 
   SplatActions.clampScalar(1, sXLen, sXLen);
 
+  LegalityPredicate ExtractSubvecBitcastPred = [=](const LegalityQuery &Query) {
+    LLT DstTy = Query.Types[0];
+    LLT SrcTy = Query.Types[1];
+    return DstTy.getElementType() == LLT::scalar(1) &&
+           DstTy.getElementCount().getKnownMinValue() >= 8 &&
+           SrcTy.getElementCount().getKnownMinValue() >= 8;
+  };
+  getActionDefinitionsBuilder(G_EXTRACT_SUBVECTOR)
+      // We don't have the ability to slide mask vectors down indexed by their
+      // i1 elements; the smallest we can do is i8. Often we are able to bitcast
+      // to equivalent i8 vectors.
+      .bitcastIf(
+          all(typeIsLegalBoolVec(0, BoolVecTys, ST), ExtractSubvecBitcastPred),
+          /*Mutation=*/nullptr)
+      .customIf(
+          LegalityPredicates::any(typeIsLegalBoolVec(0, BoolVecTys, ST),
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topperc wrote:

You can't just check type0. You have to check type1 too. If type isn't legal, the operation needs to be split before you can do custom legalization.

https://github.com/llvm/llvm-project/pull/109426