[InstCombine] Add ub-safe negation patterns (PR27817)

RKSimon · RKSimon · commit 16d2065cfc88 · 2020-03-23T12:47:32.000Z
diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
@@ -1348,6 +1348,29 @@ define i32 @PR27137(i32 %a) {
   ret i32 %s1
 }
 
+; ub-safe negation pattern
+define i32 @PR27817(i32 %x) {
+; CHECK-LABEL: @PR27817(
+; CHECK-NEXT:    [[SUB:%.*]] = sub i32 0, [[X:%.*]]
+; CHECK-NEXT:    ret i32 [[SUB]]
+;
+  %cmp = icmp eq i32 %x, -2147483648
+  %sub = sub i32 0, %x
+  %sel = select i1 %cmp, i32 -2147483648, i32 %sub
+  ret i32 %sel
+}
+
+define i32 @PR27817_nsw(i32 %x) {
+; CHECK-LABEL: @PR27817_nsw(
+; CHECK-NEXT:    [[SUB:%.*]] = sub i32 0, [[X:%.*]]
+; CHECK-NEXT:    ret i32 [[SUB]]
+;
+  %cmp = icmp eq i32 %x, -2147483648
+  %sub = sub nsw i32 0, %x
+  %sel = select i1 %cmp, i32 -2147483648, i32 %sub
+  ret i32 %sel
+}
+
 define i32 @select_icmp_slt0_xor(i32 %x) {
 ; CHECK-LABEL: @select_icmp_slt0_xor(
 ; CHECK-NEXT:    [[TMP1:%.*]] = or i32 [[X:%.*]], -2147483648
