[Bug c/8081] ICE with variably sized types returned from nested functions
rguenth at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Thu Jan 12 10:23:00 GMT 2012
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8081
--- Comment #24 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-01-12 10:23:05 UTC ---
Created attachment 26306
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26306
A patch for using by-reference passing
(In reply to comment #23)
> as alternative to rejecting this case we can lower returning variable-size
> types during un-nesting to explicit passing of a return slot and using
> memcpy, making the nested function return nothing.
It's of course not that easy as we gimplify before un-nesting. The frontend
would be responsible to arrange things that way, similar to how we pass
a return slot in the C++ frontend (DECL_BY_REFERENCE on the DECL_RESULT
variable). Like for the attached patch. Passes
extern void abort (void);
int
main (int argc, char **argv)
{
int size = 10;
typedef struct
{
char val[size];
}
block;
block a, b;
block __attribute__((noinline))
retframe_block ()
{
return *(block *) &b;
}
b.val[0] = -1;
b.val[1] = -2;
a=retframe_block ();
if (a.val[0] != -1
|| a.val[1] != -2)
abort ();
return 0;
}
I'm not sure if one can construct a testcase where using return-slot
optimization causes wrong-code generation. Alternatively checking
DECL_BY_REFERENCE on the callees DECL_RESULT instead of applying it to
all VLA types could work (though not for indirect calls).
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