https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77705
Bug ID: 77705
Summary: Optimize away some static constructors
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jakub at gcc dot gnu.org
Target Milestone: ---
struct S { int a; };
void baz (S *);
#if __cpp_constexpr >= 200704
constexpr
#endif
inline S foo () { return (S) { 2 }; }
S s = foo ();
for -std=c++98 -O2 we have the runtime initializer. If we had some pass that
would analyze the ctor functions after they were inlined into and if they only
write constants into file-scope vars defined in the current TU (except for
comdat vars?) turn the ctor function into static initializers for the
file-scope vars.
Not sure if we can do it generally for any (non-comdat?) vars, or if e.g. the
C++ FE wouldn't have to mark such vars some way for us, or if we wouldn't need
to analyze if there aren't some ctors in the same TU that would run earlier
(higher (or is that lower?) priority) and could access those vars, or for vars
visible outside of the TU if some other TU's ctor couldn't access them.
An argument for some guidance from the C++ FE would be that say in C:
int a __attribute__((nocommon));
static __attribute__((constructor)) void
foo (void)
{
a = 6;
}
some other TU could say in heither priority ctor expect to see a == 0.
