[llvm] Fix Failure to fold (and %x, (sext i1 %m)) -> (select %m, %x, 0) with multiple uses of %m Resolve #81288 (PR #81409)

[Nikita Popov via llvm-commits]

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@@ -2768,3 +2768,18 @@ define i32 @add_constant_equal_with_the_top_bit_of_demandedbits_insertpt(i32 %x,
   %and = and i32 %or, 24
   ret i32 %and
 }
+
+define i32 @and_sext(i32 %x, i32 %y, i32 %a, i32 %b) {
+; CHECK-LABEL: @and_sext(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i32 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[ADD:%.*]] = select i1 [[CMP]], i32 [[TMP1]], i32 0
+; CHECK-NEXT:    ret i32 [[ADD]]
+;
+  %cmp = icmp sgt i32 %x, %y
+  %sext = sext i1 %cmp to i32
+  %and1 = and i32 %sext, %a
+  %and2 = and i32 %sext, %b
+  %add = add i32 %and1, %and2
+  ret i32 %add
+}
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nikic wrote:

TBH, I don't think we need anything beyond this test. We already have all the necessary commuted / vector / multi-use coverage above. This test essentially just serves to illustrate why relaxing the one-use restriction is useful.

https://github.com/llvm/llvm-project/pull/81409