| Issue |
90417
|
| Summary |
Reopen of Bug 49389 - Condition not constant folded
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
tesuji
|
This old issue doesn't seem to be fixed as all: https://bugs.llvm.org/show_bug.cgi?id=49389
Bug 49389 would be reposted below (godbolt link: https://godbolt.org/z/hdza9Pb8z):
```c
#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>
#define N 1234
bool eat_digits(uint8_t s[N]) {
size_t i = 0;
while (i < N) {
uint8_t c = s[i];
if ('0' <= c && c <= '9') {
i += 1;
} else {
break;
}
}
return i <= N;
}
```
compiles to:
```asm
eat_digits: # @eat_digits
xor ecx, ecx
.LBB0_1: # =>This Inner Loop Header: Depth=1
mov rax, rcx
cmp rcx, 1234
je .LBB0_3
movzx edx, byte ptr [rdi + rax]
add dl, -48
lea rcx, [rax + 1]
cmp dl, 10
jb .LBB0_1
.LBB0_3:
cmp rax, 1235
setb al
ret
```
GCC is able to compile it to:
```asm
eat_digits:
mov eax, 1
ret
```
This is originally from: https://github.com/rust-lang/rust/issues/81432
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