https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106864
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
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Keywords| |missed-optimization
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this is just a missed optimization really.
Because GCC does the right thing inside the inner most lambda and it is
considered as a constexpr there still. But the inner lambda L has a capture
still.
You can see the missed optimization via:
void bad() {
constexpr int x = 123;
auto Outer = [&] [[gnu::noipa]] () {
auto L = [=] [[gnu::noipa]] () {
for (int i = 0; i < x; ++i) { asm("":::"memory"); }
};
//static_assert(sizeof(L) == 1); // fails
asm("":::"memory");
L();
};
Outer();
static_assert(sizeof(Outer) == 1); // fails
}
And look at the assembly for `bad()::{lambda()#1}::operator()() const` which
does the store before calling `bad()::{lambda()#1}::operator()()
const::{lambda()#1}::operator()() const`
But `bad()::{lambda()#1}::operator()() const::{lambda()#1}::operator()() const`
uses 123 always.
Even at -O2 and such.
