[llvm] [SelectionDAG] Use SimplifyDemandedBits from SimplifyDemandedVectorElts Bitcast. (PR #133717)

[Thomas Lively via llvm-commits]

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@@ -27,8 +27,8 @@ define <2 x i2> @i2x2_splat(i1 %x) {
 
 ; CHECK-LABEL: not_a_vec:
 ; CHECK-NEXT: .functype not_a_vec (i64, i64) -> (v128){{$}}
-; CHECK-NEXT: i32.wrap_i64    $push[[L:[0-9]+]]=, $0
-; CHECK-NEXT: i32x4.splat     $push[[R:[0-9]+]]=, $pop[[L]]
+; CHECK-NEXT: i64x2.splat     $push[[L:[0-9]+]]=, $0
+; CHECK-NEXT: i8x16.shuffle   $push[[R:[0-9]+]]=, $pop[[L]], $2, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3
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tlively wrote:

Looks like the test was originally added to show that an assertion was not hit, so it's still correctly showing that after this change. The actual codegen change looks like a regression, but I don't think the test is representative of common patterns, so that's probably fine. LGTM to land the patch from the Wasm point of view.

https://github.com/llvm/llvm-project/pull/133717