[Bug tree-optimization/92867] Use ERF_RETURNS_ARG in more places
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92867 Andrew Pinski changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |DUPLICATE --- Comment #7 from Andrew Pinski --- Dup of bug 67797. *** This bug has been marked as a duplicate of bug 67797 ***
[Bug tree-optimization/92867] Use ERF_RETURNS_ARG in more places
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92867 Richard Biener changed: What|Removed |Added Status|NEW |ASSIGNED
[Bug tree-optimization/92867] Use ERF_RETURNS_ARG in more places
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92867
Martin Sebor changed:
What|Removed |Added
CC||msebor at gcc dot gnu.org
--- Comment #6 from Martin Sebor ---
The "returns-argument" attribute should also be used to help detect buffer
overflow after returning from functions declared with it (either built-ins or
user-defined):
__attribute__ ((returns_arg (1))) char* f (char*);
char a[4], b[8];
void g (void)
{
memcpy (b, f (a), sizeof b); // reads 8 bytes from a
}
[Bug tree-optimization/92867] Use ERF_RETURNS_ARG in more places
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92867 --- Comment #5 from Jakub Jelinek --- GCC already has various attributes that take argument positions, e.g. the nonnull, alloc_size, format, format_arg, so we should follow what is used for those for this argument. E.g. for format_arg we document: The parameter STRING-INDEX specifies which argument is the format string argument (starting from one). Since non-static C++ methods have an implicit 'this' argument, the arguments of such methods should be counted from two. and similarly for format, for nonnull and alloc_size we don't, so it might be worth checking what we actually do. There is also the case of an artificial argument holding address to the return slot, I think that is what comes up only in RTL and would hope RTL handles it right, but it is worth checking that too.
[Bug tree-optimization/92867] Use ERF_RETURNS_ARG in more places
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92867
Ulrich Drepper changed:
What|Removed |Added
CC||drepper.fsp+rhbz at gmail dot
com
--- Comment #4 from Ulrich Drepper ---
This BZ came out of a discussion around C++ function call chaining along the
line of:
void f1(std::string& s, int a)
{
std::cout << "hello " << s;
if (a != 0)
std::cout << a;
std::cout << '\n';
}
The 'if' prevents one single series of calls through operator<< from being used
and the compiler has reload std::cout from memory every time. There are ugly
work-arounds in the source to get the desired behaviour but this should happen
automatically. The work-arounds are too ugly and there is lots of code out
there.
One way would be to expose a way to specify one of the arguments is returned.
Jakub mentioned that there is already internally a way to use the "fn spec"
attribute. How about exposing this explicitly as a function attribute?
Jakub also raised the point how this should be applied to member functions. I
suggest that the parameter for the attribute is really a number (not parameter
name) and that argument 1 (or 0, if you want the count start at zero) refers to
'this' in case of member functions.
How about this?
[Bug tree-optimization/92867] Use ERF_RETURNS_ARG in more places
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92867 --- Comment #3 from Jakub Jelinek --- Sure, go ahead.
[Bug tree-optimization/92867] Use ERF_RETURNS_ARG in more places
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92867 prathamesh3492 at gcc dot gnu.org changed: What|Removed |Added CC||prathamesh3492 at gcc dot gnu.org --- Comment #2 from prathamesh3492 at gcc dot gnu.org --- If it's OK, I will try to implement this. Thanks, Prathamesh
[Bug tree-optimization/92867] Use ERF_RETURNS_ARG in more places
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92867 Richard Biener changed: What|Removed |Added Keywords||missed-optimization Status|UNCONFIRMED |NEW Last reconfirmed||2019-12-09 Ever confirmed|0 |1 --- Comment #1 from Richard Biener --- Yes, yes and yes.
