[llvm] [RISCV] Fix illegal build_vector when lowering double id buildvec on RV32 (PR #67017)

[Luke Lau via llvm-commits]

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@@ -259,25 +259,40 @@ define <4 x i8> @buildvec_vid_stepn3_add3_v4i8() {
 ; CHECK-NEXT:    vsetivli zero, 4, e8, mf4, ta, ma
 ; CHECK-NEXT:    vmv.v.i v9, 3
 ; CHECK-NEXT:    vid.v v8
-; CHECK-NEXT:    li a0, -3
+; CHECK-NEXT:    li a0, 253
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lukel97 wrote:

This and the regressions below are caused by `SelectionDAG::getConstant` not sign-extending the splat value. I'll try to fix this in a separate PR

https://github.com/llvm/llvm-project/pull/67017