https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96846
--- Comment #2 from andysem at mail dot ru ---
(In reply to Jakub Jelinek from comment #1)
In the godbolt link there is also a third case, which is similar to the second
one, but does not reuse the source register for comparison results.
unsigned int doubletmatch(unsigned int arr[], unsigned int key)
{
unsigned count = 0;
for (int i=0; i<1024 ; i++) {
count += (arr[i] == key) | (arr[i] == ~key);
}
return count;
}
doubletmatch(unsigned int*, unsigned int):
mov r9d, esi
not r9d
lea rcx, [rdi+4096]
xor r8d, r8d
.L7:
mov edx, DWORD PTR [rdi]
cmp edx, esi
sete al
cmp edx, r9d
sete dl
or eax, edx
movzx eax, al
add rdi, 4
add r8d, eax
cmp rcx, rdi
jne .L7
mov eax, r8d
ret
Note that in this case eax is not cleared either, so the "or eax, edx" has a
dependency on whatever prior instruction wrote to eax (before sete).
