[llvm] [InstCombine] Fold `(add X, (sext/zext (icmp eq X, C)))` (PR #93840)

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,56 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+declare void @use.i8(i8)
+define i8 @fold_add_zext_eq_0(i8 %x) {
+; CHECK-LABEL: @fold_add_zext_eq_0(
+; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.umax.i8(i8 [[X:%.*]], i8 1)
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %x_eq = icmp eq i8 %x, 0
+  %x_eq_ext = zext i1 %x_eq to i8
+  %r = add i8 %x, %x_eq_ext
+  ret i8 %r
+}
+
+define i8 @fold_add_sext_eq_4(i8 %x) {
+; CHECK-LABEL: @fold_add_sext_eq_4(
+; CHECK-NEXT:    [[X_EQ:%.*]] = icmp eq i8 [[X:%.*]], 4
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[X_EQ]], i8 3, i8 [[X]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %x_eq = icmp eq i8 %x, 4
+  %x_eq_ext = sext i1 %x_eq to i8
+  %r = add i8 %x, %x_eq_ext
+  ret i8 %r
+}
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nikic wrote:

Commuted tests?

https://github.com/llvm/llvm-project/pull/93840