https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105670
Bug ID: 105670
Summary: [x86] suboptimal code for branch over two bools
Product: gcc
Version: 12.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: fent at in dot tum.de
Target Milestone: ---
void test(bool a, bool b, int* t) {
if (a & b)
*t = 42;
}
With -O1, -O2, -O3, and -Os this produces:
test(bool, bool, int*):
test dil, dil
je .L1
test sil, sil
je .L1
mov DWORD PTR [rdx], 42
.L1:
ret
The following would be 5B shorter and also faster, since it minimizes branch
misses:
test(bool, bool, int*):
test sil, dil
je .L1
mov DWORD PTR [rdx], 42
.L1:
ret
Note that this is (somewhat) ABI dependent, but works on x86-64 System V,
since:
> bit 0 contains the truth value and bits 1 to 7 shall be zero
