[llvm] [SelectionDAG] Simplify vselect true, T, F -> T (PR #100992)

[Luke Lau via llvm-commits]

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@@ -0,0 +1,10 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=riscv64 -mattr=+v -verify-machineinstrs | FileCheck %s
+
+define <vscale x 1 x i64> @all_ones(<vscale x 1 x i64> %true, <vscale x 1 x i64> %false, i32 %evl) {
+; CHECK-LABEL: all_ones:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    ret
+  %v = call <vscale x 1 x i64> @llvm.vp.select.nxv1i64(<vscale x 1 x i1> splat (i1 true), <vscale x 1 x i64> %true, <vscale x 1 x i64> %false, i32 %evl)
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lukel97 wrote:

I tried creating a test case on r600 which seems to have the different behaviour but couldn't come up with anything meaningful. Mainly because the combine kicks in when the condition vector is at nxi1, so every behaviour considers it true.

https://github.com/llvm/llvm-project/pull/100992