[llvm] [SCEV] Use or disjoint flag (PR #74467)

[Nikita Popov via llvm-commits]

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@@ -6,15 +6,49 @@ define i8 @or-of-constant-with-no-common-bits-set(i8 %x, i8 %y) {
 ; CHECK-NEXT:  Classifying expressions for: @or-of-constant-with-no-common-bits-set
 ; CHECK-NEXT:    %t0 = shl i8 %x, 2
 ; CHECK-NEXT:    --> (4 * %x) U: [0,-3) S: [-128,125)
-; CHECK-NEXT:    %r = or i8 %t0, 3
+; CHECK-NEXT:    %r = or disjoint i8 %t0, 3
 ; CHECK-NEXT:    --> (3 + (4 * %x))<nuw><nsw> U: [3,0) S: [-125,-128)
 ; CHECK-NEXT:  Determining loop execution counts for: @or-of-constant-with-no-common-bits-set
 ;
   %t0 = shl i8 %x, 2
-  %r = or i8 %t0, 3
+  %r = or disjoint i8 %t0, 3
   ret i8 %r
 }
 
+define i8 @or-disjoint(i8 %x, i8 %y) {
+; CHECK-LABEL: 'or-disjoint'
+; CHECK-NEXT:  Classifying expressions for: @or-disjoint
+; CHECK-NEXT:    %or = or disjoint i8 %x, %y
+; CHECK-NEXT:    --> (%x + %y) U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @or-disjoint
+;
+  %or = or disjoint i8 %x, %y
+  ret i8 %or
+}
+
+define i8 @or-no-disjoint(i8 %x, i8 %y) {
+; CHECK-LABEL: 'or-no-disjoint'
+; CHECK-NEXT:  Classifying expressions for: @or-no-disjoint
+; CHECK-NEXT:    %or = or i8 %x, %y
+; CHECK-NEXT:    --> %or U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @or-no-disjoint
+;
+  %or = or i8 %x, %y
+  ret i8 %or
+}
+
+; FIXME: We could add nuw nsw flags here.
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nikic wrote:

I added some tests to make sure we don't incorrectly add the nuw/nsw flags if poison doesn't imply UB, but found that we actually never transfer these. This is because the NSW/NUW flags set in MatchBinaryOp end up being ignored in favor of the ones on the original instruction. I'll fix that in a followup.

https://github.com/llvm/llvm-project/pull/74467