https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85799
Bug ID: 85799
Summary: __builin_expect doesn't propagate through inlined
functions
Product: gcc
Version: 8.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redbeard0531 at gmail dot com
Target Milestone: ---
It seems like __builtin_expect doesn't propagate to conditions when inlined.
This is unfortunate because in some cases it would be nice to be able to put
the expectation into methods so that every user doesn't need to do their own
hinting. Currently we need to use macros to achieve this.
See https://godbolt.org/g/MuPM77 for full example
inline bool expect_false(bool b) {
return __builtin_expect(b, false);
}
void inline_func_hint(bool b) {
if (expect_false(b)) {
unlikely(); // treated as more likely!!!
} else {
likely();
}
}
inline_func_hint(bool):
test dil, dil
je .L11
jmp unlikely()
.L11:
jmp likely()
