[llvm] [ValueTracking] Handle flipped strictness cases in `matchSelectPattern` (PR #121958)

[Nikita Popov via llvm-commits]

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@@ -19,6 +19,18 @@ define i32 @foo(i32 %h) {
   ret i32 %r
 }
 
+define i32 @foo_commuted(i32 %h) {
+; CHECK-LABEL: @foo_commuted(
+; CHECK-NEXT:    [[SD:%.*]] = sdiv i32 [[H:%.*]], 2
+; CHECK-NEXT:    [[R:%.*]] = call i32 @llvm.smin.i32(i32 [[SD]], i32 1)
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %sd = sdiv i32 %h, 2
+  %t = icmp sgt i32 %sd, 0
+  %r = select i1 %t, i32 1, i32 %sd
+  ret i32 %r
+}
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nikic wrote:

Do I understand correctly that the reason why this only matters in cases like this is that usually tryToReuseConstantFromSelectInComparison will convert it into a form that SPF recognizes, and what this change effectively does is just make the bailout for simplifying icmps that are part of a min/max pattern stronger?

https://github.com/llvm/llvm-project/pull/121958