[Bug c++/107360] ICE on sizeof(*f(x)) when f's (deduced) return type is a pointer to VLA
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107360 --- Comment #5 from Martin Uecker --- Yes. After reconsidering this, this is not related to the other bugs mentioned above. I think your first example needs to be invalid, because the derived return type then depends on a variable inside the nested functions, which can not work without new pointer types. The second example could work.
[Bug c++/107360] ICE on sizeof(*f(x)) when f's (deduced) return type is a pointer to VLA
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107360
--- Comment #4 from Alexey Izbyshev ---
(In reply to Martin Uecker from comment #3)
> I think there there are cases were variably modified
> return types are allowed in ISO C:
>
> void f(int n, double (*(bar(void)))[n])
> {
> double (*p)[n] = bar();
> }
Yes, I should have been more precise. Per C11 6.7.6.2:
> If an identifier is declared as having a variably modified type, it shall be
> an ordinary identifier (as defined in 6.2.3), have no linkage, and have
> either block scope or function prototype scope.
So, since my original example is in C++ and involves return type deduction,
what I really wanted to say is that it's not allowed to *define* a function
with a variably modified return type in ISO C (hence it seems fine to not
support it in GCC's VLA extension for C++ too and consider such code invalid).
GCC does allow to define a nested function with a variably modified return type
though, and, perhaps surprisingly, a test case similar to my original C++ one
is compiled successfully:
extern int n;
int f() {
int a[n];
int (*g())[n] {
return &a;
};
return sizeof *g();
}
But what would seem to be a C++ equivalent crashes GCC:
extern int n;
int f() {
int a[n];
auto g = [&]() {
return &a;
};
return sizeof *g();
}
during RTL pass: expand
: In function 'int f()':
:6:13: internal compiler error: in expand_expr_real_1, at expr.cc:10586
6 | return &a;
| ^
...
And for this one it's less clear to me whether GCC wants to consider it
invalid.
But without return type deduction GCC refuses to compile:
extern int n;
int f() {
typedef int t[n];
t a;
auto g = [&]() -> t* {
return &a;
};
return sizeof *g();
}
: In function 'int f()':
:6:12: error: data member may not have variably modified type 'int
(*())[n]'
6 | auto g = [&]() -> t* {
|^
:6:12: error: declaration of 'operator()' as non-function
Compiler returned: 1
[Bug c++/107360] ICE on sizeof(*f(x)) when f's (deduced) return type is a pointer to VLA
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107360
Martin Uecker changed:
What|Removed |Added
CC||muecker at gwdg dot de
--- Comment #3 from Martin Uecker ---
This is likely related to PR108423 and PR107557.
I think there there are cases were variably modified
return types are allowed in ISO C:
void f(int n, double (*(bar(void)))[n])
{
double (*p)[n] = bar();
}
[Bug c++/107360] ICE on sizeof(*f(x)) when f's (deduced) return type is a pointer to VLA
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107360
--- Comment #2 from Alexey Izbyshev ---
(In reply to Andrew Pinski from comment #1)
> Maybe this should be invalid code ...
Yes, I think it should be invalid. VLAs are not allowed in function return
types in C. VLAs in C++ are a GCC extension, but it's unclear to me why (and
how) GCC should allow them in return types, even when they don't depend on
function parameters.
Currently, GCC crashes even in the latter case, e.g.:
extern int n;
auto f() {
int (*a)[n] = 0;
return a;
}
int g() {
return sizeof *f();
}
[Bug c++/107360] ICE on sizeof(*f(x)) when f's (deduced) return type is a pointer to VLA
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107360 Andrew Pinski changed: What|Removed |Added Keywords|ice-on-valid-code | --- Comment #1 from Andrew Pinski --- Maybe this should be invalid code ...
