[llvm] [AArch64][GlobalISel] Refactor BITCAST Legalization (PR #80505)

[Matt Arsenault via llvm-commits]

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@@ -5342,6 +5380,20 @@ LegalizerHelper::moreElementsVector(MachineInstr &MI, unsigned TypeIdx,
     Observer.changedInstr(MI);
     return Legalized;
   }
+  case TargetOpcode::G_BITCAST: {
+    if (TypeIdx != 0)
+      return UnableToLegalize;
+
+    unsigned SrcScalSize =
+        MRI.getType(MI.getOperand(1).getReg()).getScalarSizeInBits();
+    LLT NewTy =
+        LLT::fixed_vector(MoreTy.getSizeInBits() / SrcScalSize, SrcScalSize);
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arsenm wrote:

Can you keep this in terms of TypeSize and avoid the fixed_vector?

https://github.com/llvm/llvm-project/pull/80505