[Bug c++/102704] NRVO for throw expression
redi at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Wed Oct 13 08:43:56 GMT 2021
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102704
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed| |2021-10-13
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
[class.copy.elision] p1:
This elision of copy/move operations, called copy elision, is permitted in the
following circumstances (which may be combined to eliminate multiple copies):
-- in a return statement [...]
-- in a throw-expression (7.6.18), when the operand is the name of a
non-volatile object with automatic storage duration (other than a function or
catch-clause parameter) that belongs to a scope that does not contain the
innermost enclosing compound-statement associated with a try-block (if there is
one), the copy/move operation can be omitted by constructing the object
directly into the exception object
-- in a coroutine [...]
-- when the exception-declaration of an exception handler [...]
The slightly confusing "does not contain the innermost enclosing
compound-statement" means you can't elide if the throw is in a try-block and
the variable was defined outside it.
So this cannot be elided:
void f()
{
mytype x;
try {
throw x;
} catch (int) {
}
}
But this can be:
void g()
{
try {
mytype x;
throw x;
} catch (int) {
}
}
And the example in comment 0 can be.
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