https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109112
Bug ID: 109112
Summary: [missed optimization] odd behaviour with
[[assume(...)]] and member variables
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ivan.lazaric.gcc at gmail dot com
Target Milestone: ---
Everything is built with flags: -std=c++23 -O3
[[assume(...)]] doesn't seem to work quite as well when dealing with member
variables.
First version of `fn`:
void do_something();
void fn(bool x){
[[assume(!x)]];
if (x) do_something();
}
`fn` compiles into nothing:
fn(bool):
ret
Second version of `fn`, wrapping the `bool` argument in a simple struct:
struct S { bool x; };
void do_something();
void fn(S s){
[[assume(!s.x)]];
if (s.x) do_something();
}
This no longer compiles into just `ret`:
fn(S):
test dil, dil
jne .L5
ret
.L5:
jmp do_something()
Expected behaviour was for `fn(S)` to reduce to just `ret`
Godbolt link with the examples: https://godbolt.org/z/nreM4Y6dW
