[llvm] [InstCombine] Detect uadd with overflow idiom (PR #140178)

[Craig Topper via llvm-commits]

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@@ -147,3 +147,76 @@ define { <2 x i32>, <2 x i1> } @fold_simple_splat_constant_with_or_fail(<2 x i32
   %b = tail call { <2 x i32>, <2 x i1> } @llvm.uadd.with.overflow.v2i32(<2 x i32> %a, <2 x i32> <i32 30, i32 30>)
   ret { <2 x i32>, <2 x i1> } %b
 }
+
+define i32 @uadd_with_zext(i32 %x, i32 %y) {
+; CHECK-LABEL: @uadd_with_zext(
+; CHECK-NEXT:    [[UADD:%.*]] = call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
+; CHECK-NEXT:    [[CMP:%.*]] = extractvalue { i32, i1 } [[UADD]], 1
+; CHECK-NEXT:    [[COND:%.*]] = zext i1 [[CMP]] to i32
+; CHECK-NEXT:    ret i32 [[COND]]
+;
+  %conv = zext i32 %x to i64
+  %conv1 = zext i32 %y to i64
+  %add = add i64 %conv, %conv1
+  %cmp = icmp ugt i64 %add, 4294967295
+  %cond = zext i1 %cmp to i32
+  ret i32 %cond
+}
+
+define i32 @uadd_with_zext_use_and(i32 %x, i32 %y) {
+; CHECK-LABEL: @uadd_with_zext_use_and(
+; CHECK-NEXT:    [[UADD:%.*]] = call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
+; CHECK-NEXT:    [[UADD_VALUE:%.*]] = extractvalue { i32, i1 } [[UADD]], 0
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[UADD_VALUE]], 65536
+; CHECK-NEXT:    [[AND:%.*]] = zext nneg i32 [[TMP1]] to i64
+; CHECK-NEXT:    call void @usei64(i64 [[AND]])
+; CHECK-NEXT:    [[CMP:%.*]] = extractvalue { i32, i1 } [[UADD]], 1
+; CHECK-NEXT:    [[COND:%.*]] = zext i1 [[CMP]] to i32
+; CHECK-NEXT:    ret i32 [[COND]]
+;
+  %conv = zext i32 %x to i64
+  %conv1 = zext i32 %y to i64
+  %add = add i64 %conv, %conv1
+  %and = and i64 %add, 65536
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topperc wrote:

This is a bit of an odd choice of constant. 65536 has a single bit set. Something closer to 4294967295 would match the intent of the check in the code.

https://github.com/llvm/llvm-project/pull/140178