https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114305
Bug ID: 114305
Summary: GCC doesn't use [[gnu::pure]] attribute on the inline
function
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: khim at google dot com
Target Milestone: ---
The following program is an illustration (https://godbolt.org/z/PYW34ccvP):
#include <cstddef>
GNU_PURE1 extern size_t foo(size_t);
template <size_t size>
GNU_PURE2 inline size_t test() {
return foo(size);
}
int test_func(int x, int y) {
return test<sizeof x>() + test<sizeof y>();
}
If GNU_PURE1 is [[gnu::pure]] then both gcc and clang optimize away second
call, if GNU_PURE2 is [[gnu::pure]] then only clang does that.
That means that it's impossible to add [[gnu::pure]] optimization on top of
function that's pure according to the docs but is not declared as such in the
header file.
