[llvm] [RISCV] Select zero splats of EEW=64 on RV32 (PR #107205)

[Craig Topper via llvm-commits]

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@@ -3452,10 +3452,37 @@ bool RISCVDAGToDAGISel::selectVSplat(SDValue N, SDValue &SplatVal) {
   return true;
 }
 
+// Look for splats of zero. On RV32 a EEW=64 there may be a bitcast in between.
+//
+//   t72: nxv16i32 = RISCVISD::VMV_V_X_VL ...
+//   t73: v32i32 = extract_subvector t72, Constant:i32<0>
+//   t21: v16i64 = bitcast t73
+//   t42: nxv8i64 = insert_subvector undef:nxv8i64, t21, Constant:i32<0>
+static bool isZeroSplat(SDValue N) {
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topperc wrote:

Proposed patch https://github.com/llvm/llvm-project/pull/107290

https://github.com/llvm/llvm-project/pull/107205