http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53637
Bug #: 53637
Summary: NRVO not applied in branches when it could be
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: [email protected]
ReportedBy: [email protected]
In the example below it should be possible to apply NRVO. This situation is
similar to, but more complicated than, the one reported in PR51571.
Note that while this is "just a missed optimization", NRVO can affect the way
interfaces are designed, so aggressively covering all possible cases seems more
important than with most optimizations.
$ cat nrvo.cc
class Foo {
public:
Foo() {}
// Declare but don't define so that if NRVO doesn't kick in we
// get a linker error.
Foo(const Foo& other);
};
Foo bar(int i) {
if (i > 1) {
Foo result;
return result;
} else {
Foo result;
return result;
}
}
int main(int argc, char* argv[]) {
Foo f = bar(argc);
}
$ g++-4.7 -O2 nrvo.cc
/tmp/ccRlHce1.o: In function `bar(int)':
nrvo.cc:(.text+0xe): undefined reference to `Foo::Foo(Foo const&)'
collect2: error: ld returned 1 exit status
$ g++-4.7 --version
g++-4.7 (Ubuntu/Linaro 4.7.0-7ubuntu3) 4.7.0
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
