[llvm] [RISCV][GISEL] Legalize G_BITCAST for scalable vectors (PR #85970)

[Matt Arsenault via llvm-commits]

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@@ -155,6 +155,9 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
 
   getActionDefinitionsBuilder(G_BITREVERSE).maxScalar(0, sXLen).lower();
 
+  getActionDefinitionsBuilder(G_BITCAST).legalIf(
+      all(isScalableVector(0), isScalableVector(1)));
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arsenm wrote:

No. In the legality rules, there's no need to ensure you only claim valid bitcasts are legal. 
Independently of that, I would expect you need to limit this to supported element sizes 


https://github.com/llvm/llvm-project/pull/85970