[Bug c++/58063] default arguments evaluated twice per call
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 Jason Merrill changed: What|Removed |Added Status|NEW |RESOLVED Known to work||4.9.4, 5.2.0, 6.0 Resolution|--- |FIXED Target Milestone|--- |4.9.4 --- Comment #17 from Jason Merrill --- This was fixed a while back.
[Bug c++/58063] default arguments evaluated twice per call
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #16 from Jason Merrill --- Author: jason Date: Tue Aug 18 14:43:38 2015 New Revision: 226973 URL: https://gcc.gnu.org/viewcvs?rev=226973&root=gcc&view=rev Log: PR c++/58063 * tree.c (bot_manip): Remap SAVE_EXPR. Added: branches/gcc-4_9-branch/gcc/testsuite/g++.dg/overload/defarg10.C Modified: branches/gcc-4_9-branch/gcc/cp/ChangeLog branches/gcc-4_9-branch/gcc/cp/tree.c
[Bug c++/58063] default arguments evaluated twice per call
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 Ville Voutilainen changed: What|Removed |Added CC||ville.voutilainen at gmail dot com --- Comment #15 from Ville Voutilainen --- *** Bug 61856 has been marked as a duplicate of this bug. ***
[Bug c++/58063] default arguments evaluated twice per call
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #14 from Jason Merrill --- Author: jason Date: Wed Jun 17 14:33:17 2015 New Revision: 224559 URL: https://gcc.gnu.org/viewcvs?rev=224559&root=gcc&view=rev Log: PR c++/58063 * tree.c (bot_manip): Remap SAVE_EXPR. Added: branches/gcc-5-branch/gcc/testsuite/g++.dg/overload/defarg10.C Modified: branches/gcc-5-branch/gcc/cp/ChangeLog branches/gcc-5-branch/gcc/cp/tree.c
[Bug c++/58063] default arguments evaluated twice per call
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #13 from Jason Merrill --- Author: jason Date: Tue Jun 16 19:29:09 2015 New Revision: 224533 URL: https://gcc.gnu.org/viewcvs?rev=224533&root=gcc&view=rev Log: PR c++/58063 * tree.c (bot_manip): Remap SAVE_EXPR. Added: trunk/gcc/testsuite/g++.dg/overload/defarg10.C Modified: trunk/gcc/cp/ChangeLog trunk/gcc/cp/tree.c
[Bug c++/58063] default arguments evaluated twice per call
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #12 from plokinom at gmail dot com --- I can confirm this still happens with g++ 5.1.0.
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 Paolo Carlini changed: What|Removed |Added Keywords||wrong-code Priority|P3 |P2 Status|UNCONFIRMED |NEW Last reconfirmed||2013-08-04 CC||jason at gcc dot gnu.org Ever confirmed|0 |1 --- Comment #11 from Paolo Carlini --- Thanks!
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063
Fanael changed:
What|Removed |Added
CC||fanael4 at gmail dot com
--- Comment #10 from Fanael ---
My attempt at reducing:
struct basic_ios
{
virtual ~basic_ios() {}
bool operator!() const { return false; }
};
struct ostream : virtual basic_ios
{
ostream() {}
~ostream() {}
private:
ostream(const ostream&);
ostream& operator=(const ostream&);
};
ostream& operator<<(ostream& os, const char* s) {
__builtin_printf("%s", s);
return os;
}
ostream cout;
void f(bool x = !(cout << "hi!\n")) {
__builtin_printf("%d\n", static_cast(x));
}
int main() {
f();
}
Seems like virtual inheritance is the culprit.
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #9 from Paolo Carlini --- Your help is always very appreciated, Daniel. Here we have plenty of work to do anyway, if when you will back the bug will be unchanged, consider helping more.
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #8 from Daniel Krügler --- (In reply to Paolo Carlini from comment #7) > But it happens with -O0 too, right? Yes. > In any case we badly need a reduced testcase ;) I agree. Unfortunately I'm on vacations from tomorrow on (1 week), so I cannot look into it until next week.
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #7 from Paolo Carlini --- I'm not at all sure! But it happens with -O0 too, right?, thus at this point the front-end seems more likely than the back-end, I would not change the Component from c++ to something else. In any case we badly need a reduced testcase ;)
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063
--- Comment #6 from Daniel Krügler ---
(In reply to Paolo Carlini from comment #5)
> Ah, in case isn't obvious already: it only happens when the "I/O expression"
> has the ! operator in front.
I suspected that and ensured that I added a similar operator! to my ostream
model type, but this hadn't any impact on the outcome for that type. Further, I
don't understand how it is related to ostream initialization, because the issue
also occurs when we invert the order of the function calls:
int main() {
f2();
std::cout << "--\n";
f();
}
gives me:
hi!
0
--
hi!
hi!
0
Are you sure that this is not due to improper code generation?
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #5 from Paolo Carlini --- Ah, in case isn't obvious already: it only happens when the "I/O expression" has the ! operator in front.
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #4 from Paolo Carlini --- Sorry, I didn't study it in sufficient detail. Anyway, no mysteries, this is free software: libstdc++-v3/src/c++98/ios_init.cc etc.
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #3 from Daniel Krügler --- (In reply to Paolo Carlini from comment #2) > I suppose a minimal reproducer could involve a file scope static of some > sort... I'm a bit confused by your reply, Paolo: Isn't my_cout also a "file scope static"? (Even, if I declare it to have static linkage, it still behaves differently compared to std::cout)
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063 --- Comment #2 from Paolo Carlini --- The standard streams are indeed special, being constructed once and never destroyed, see libstdc++-v3/src/c++98/ios_init.cc. I suppose a minimal reproducer could involve a file scope static of some sort...
[Bug c++/58063] default arguments evaluated twice per call
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58063
Daniel Krügler changed:
What|Removed |Added
CC||daniel.kruegler@googlemail.
||com
--- Comment #1 from Daniel Krügler ---
The behavior looks indeed odd to me (and I can confirm it for gcc 4.9 as well).
I suspect at the moment that it is somehow related to the very specific
definition of std::cout, because when I try to mimic the problem for a model
type like the following, I cannot produce this effect:
//-
#include
struct my_ostream
{
my_ostream(){}
virtual ~my_ostream() {}
operator void*() const { return const_cast(this); }
bool operator!() const { return false; }
private:
my_ostream(const my_ostream&);
my_ostream& operator=(const my_ostream&);
} my_cout;
my_ostream& operator<<(my_ostream& os, const char* s)
{
std::cout << s;
return os;
}
void f(bool x = !(std::cout << "hi!\n")) {
std::cout << x << '\n';
}
void f2(bool x = !(my_cout << "hi!\n")) {
std::cout << x << '\n';
}
int main() {
f();
std::cout << "--\n";
f2();
}
//-
gives the output:
hi!
hi!
0
--
hi!
0
Looking at the generate assembly (mingw 64 but), I see the following relevant
lines:
0x004017ADlea0x7a86d(%rip),%rdx# 0x47c021
0x004017B4mov0x7e4a5(%rip),%rcx# 0x47fc60 <.refptr._ZSt4cout>
0x004017BBcallq 0x4624c0
>(std::basic_ostream >&, char const*)>
0x004017C0mov%rax,%rbx
0x004017C3lea0x7a857(%rip),%rdx# 0x47c021
0x004017CAmov0x7e48f(%rip),%rcx# 0x47fc60 <.refptr._ZSt4cout>
0x004017D1callq 0x4624c0
>(std::basic_ostream >&, char const*)>
0x004017D6mov(%rax),%rax
0x004017D9sub$0x18,%rax
0x004017DDmov(%rax),%rax
0x004017E0add%rbx,%rax
0x004017E3mov%rax,%rcx
0x004017E6callq 0x433f60
>::operator!() const>
0x004017EBmovzbl %al,%eax
0x004017EEmov%eax,%ecx
