[llvm-branch-commits] [llvm] [ConstantFolding] Add constant folding for mask.beforefirst (PR #234472)

[Luke Lau via llvm-branch-commits]

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@@ -0,0 +1,58 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt -p instsimplify -S < %s | FileCheck %s
+
+define <4 x i1> @v4i1_zero() {
+; CHECK-LABEL: define <4 x i1> @v4i1_zero() {
+; CHECK-NEXT:    ret <4 x i1> splat (i1 true)
+;
+  %res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> zeroinitializer)
+  ret <4 x i1> %res
+}
+
+define <4 x i1> @v4i1_ones() {
+; CHECK-LABEL: define <4 x i1> @v4i1_ones() {
+; CHECK-NEXT:    ret <4 x i1> zeroinitializer
+;
+  %res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> splat (i1 true))
+  ret <4 x i1> %res
+}
+
+define <4 x i1> @v4i1() {
+; CHECK-LABEL: define <4 x i1> @v4i1() {
+; CHECK-NEXT:    ret <4 x i1> <i1 true, i1 false, i1 false, i1 false>
+;
+  %res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> <i1 false, i1 true, i1 false, i1 true>)
+  ret <4 x i1> %res
+}
+
+define <4 x i1> @v4i1_poison() {
+; CHECK-LABEL: define <4 x i1> @v4i1_poison() {
+; CHECK-NEXT:    ret <4 x i1> poison
+;
+  %res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> <i1 false, i1 true, i1 poison, i1 false>)
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lukel97 wrote:

Also worth noting that this matches the current cttz.elts semantics used by the loop vectorizer today. We need to freeze the early exit condition regardless because lanes past it are used in a variety of other places, e.g. when checking that any lane has exited we use a vector.reduce.or reduction

https://github.com/llvm/llvm-project/pull/234472