https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88797
Bug ID: 88797
Summary: Unneeded branch added when function is inlined
(function runs faster if not inlined)
Product: gcc
Version: 8.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: cassio.neri at gmail dot com
Target Milestone: ---
Consider:
void use(unsigned);
bool f(unsigned x, unsigned y) {
return x < 1111 + (y <= 2222);
}
void test_f(unsigned x, unsigned y) {
for (unsigned i = 0; i < 3333; ++i)
use(f(x++, y++));
}
The generated code for f seems fine and the there's no branch to test y <=
2222:
f(unsigned int, unsigned int):
xorl %eax, %eax
cmpl $2222, %esi
setbe %al
addl $1111, %eax
cmpl %edi, %eax
seta %al
ret
However, when f is inlined in test_f, a branch is introduced to decide whether
x should be compared to 1111 or 1112 (code cut for brevity)
test_f(unsigned int, unsigned int):
[...]
jmp .L6
.L14:
cmpl $1111, %eax
.L12:
[...]
.L6:
[...]
cmpl $2222, %ebx
jbe .L14
cmpl $1110, %eax
jmp .L12
[...]
See https://godbolt.org/z/_EC992 use -O3.
This seems to be a regression: it used to be OK up to 6.3 and then degraded in
7.1 (according to godbolt).
