lea esi, [rdx - 32]+cmp edx, 32+mov edx, esi => sub edx, 32 #163125
Description
[Zig Godbolt]
[C Godbolt]
[LLVM Godbolt]
Here's some C code:
#include <stdint.h>
#include <immintrin.h>
uint32_t foo(uint8_t byte) {
uint32_t q = byte;
uint32_t acc = 0;
while (1) {
uint32_t mask = _bzhi_u32(~0u, q);
acc ^= mask;
int br = q <= 16;
q -= 16;
if (br) break;
}
return acc;
}Compiles to: (current in red, ideal in green)
foo:
mov ecx, -1
xor eax, eax
.LBB0_1:
bzhi edx, ecx, edi
xor eax, edx
- lea edx, [rdi - 16]
- cmp edi, 16
- mov edi, edx
+ sub edi, 16
ja .LBB0_1
ret