[llvm] [X86][DAGCombiner][SelectionDAG] - Fold Zext Build Vector to Bitcast of widen Build Vector (PR #135010)

[Rohit Aggarwal via llvm-commits]

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@@ -14195,6 +14195,66 @@ static SDValue widenAbs(SDNode *Extend, SelectionDAG &DAG) {
   return DAG.getZExtOrTrunc(NewAbs, SDLoc(Extend), VT);
 }
 
+// Try to widen the build vector and bitcast it to the type of zext.
+// This is a special case for the 128-bit vector types. Intention is to remove
+// the zext and replace it with a bitcast the wider type. While lowering
+// the bitcast is removed and extra commutation due to zext is avoided.
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rohitaggarwal007 wrote:

@arsenm Add such comment like  zext(build_vec) -> bitcast(build_vec). which visualize the transformation, right?

https://github.com/llvm/llvm-project/pull/135010