https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117925
Bug ID: 117925
Summary: ice unexpected expression '(FnPtr)(fnPtr)' of kind
cast_expr
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: rogerio.souza at gmail dot com
Target Milestone: ---
GCC 14 returns a compiler internal error for the code below
(https://godbolt.org/z/b8EenvKj8):
************
using FnPtr = int(*)();
template <int T>
void fnICE(void* fnPtr)
{
((FnPtr)fnPtr)();
}
************
The error message is:
************
<source>: In function 'void fnICE(void*)':
<source>:6:6: internal compiler error: unexpected expression '(FnPtr)(fnPtr)'
of kind cast_expr
6 | ((FnPtr)fnPtr)();
| ~^~~~~~~~~~~~~
0x2031cbc internal_error(char const*, ...)
???:0
0x7f6550 cp_get_fndecl_from_callee(tree_node*, bool)
???:0
0x7f6be1 convert_to_void(tree_node*, impl_conv_void, int)
???:0
0x95bca1 finish_expr_stmt(tree_node*)
???:0
0x90ee14 c_parse_file()
???:0
0xa0d1b9 c_common_parse_file()
???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
Compiler returned: 1
************
It is interesting that the code is "(ucis_InternalSetValueRangePtr)fnPtr)", but
the GCC reports it as "(ucis_InternalSetValueRangePtr)(fnPtr)", with one
parenthese before "fnPtr".
>From man 3 dlopen:
/* According to the ISO C standard, casting between function
pointers and 'void *', as done above, produces undefined results.
POSIX.1-2003 and POSIX.1-2008 accepted this state of affairs and
proposed the following workaround:
*(void **) (&cosine) = dlsym(handle, "cos");
This (clumsy) cast conforms with the ISO C standard and will
avoid any compiler warnings.
The 2013 Technical Corrigendum to POSIX.1-2008 (a.k.a.
POSIX.1-2013) improved matters by requiring that conforming
implementations support casting 'void *' to a function pointer.
Nevertheless, some compilers (e.g., gcc with the '-pedantic'
option) may complain about the cast used in this program. */
Based on this we were able to provide the work around
(https://godbolt.org/z/jaKhPWPvT):
***************
using FnPtr = int(*)();
template <int T>
void fnICE(void* fnPtr)
{
FnPtr fn;
*(void**) &fn = fnPtr;
fn();
}
***************
Although we have the workaround GCC should not ICE, so I consider it a real bug
that should be fixed.
