https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70734
Bug ID: 70734
Summary: __builtin_add_overflow emits poor code on x86-64
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: arigo at tunes dot org
Target Milestone: ---
Tested on gcc_5_branch:
extern void abort(void);
void f(int a, int b, int *r)
{
if (__builtin_add_overflow(a, b, r))
abort();
}
Results in this x86-64 assembler (xgcc -O2 -S):
xorl %eax, %eax
addl %edi, %esi
seto %al
movl %esi, (%rdx)
testl %eax, %eax
jne .L8
I would expect code with a direct "jo" instead of "seto/test/jne". I guess it
is a known issue related to the difficulties of returning the condition code
from an asm() statement. Still, I would have expected this builtin to work
around that issue.
