https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81914
Bug ID: 81914
Summary: gcc 7.1 generates branch for code which was branchless
in earlier gcc version
Product: gcc
Version: 7.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: bugzi...@poradnik-webmastera.com
Target Milestone: ---
Code:
#include <stdint.h>
int cmp(int64_t a, int64_t b)
{
return a < b ? -1 : a > b;
}
Above function compiled with gcc 4.5 or above and -O2 is compiled in following
way. It is branchless:
cmp(long, long):
xor eax, eax
cmp rdi, rsi
mov edx, -1
setg al
cmovl eax, edx
ret
gcc 7.1 generates different code. It has branch:
cmp(long, long):
cmp rdi, rsi
jl .L3
setg al
movzx eax, al
ret
.L3:
mov eax, -1
ret
