| Issue |
146131
|
| Summary |
Missed optimization when `b - a` is known nonnegative
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Explorer09
|
This issue is consider a follow-up of #142283.
I just found out additional scenarios where `b - a` (both signed integer types) can be known nonnegative.
```c
#include <stdint.h>
uint64_t func1(int32_t a, int32_t b) {
if (b < a)
a = b;
return (int32_t)(b - a);
}
uint64_t func2(int32_t a, int32_t b) {
if (b < a)
a = b;
return (uint32_t)(b - a);
}
uint64_t func3(int32_t a, int32_t b) {
return (b < a ? 0 : (int32_t)(b - a));
}
uint64_t func4(int32_t a, int32_t b) {
return (b < a ? 0 : (uint32_t)(b - a));
}
```
All four functions are equivalent. `b - a` should be known nonnegative in all four cases. In x86-64, for example, it would make shorter code by zero-extending instead of sign-extending `b - a`.
The optimizer should also be able to recognize `b - b` and optimize to constant `0`, but that's not part of the issue I'm filing now.
![]()
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
