[PATCH] Make __PRETTY_FUNCTION__-like functions mergeable string csts (PR c++/64266).

[Jason Merrill]

On Tue, Oct 23, 2018 at 4:59 AM Martin Liška <mliska@suse.cz> wrote:
> However, I still see some minor ICEs, it's probably related to decay_conversion in cp_fname_init:
>
> 1) ./xg++ -B. /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-__func__2.C
>
> /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-__func__2.C:6:17: internal compiler error: Segmentation fault
> 6 |     [] { return __func__; }();
>   |                 ^~~~~~~~
> 0x1344568 crash_signal
>         /home/marxin/Programming/gcc/gcc/toplev.c:325
> 0x7ffff6bc310f ???
>         /usr/src/debug/glibc-2.27-6.1.x86_64/signal/../sysdeps/unix/sysv/linux/x86_64/sigaction.c:0
> 0x9db134 is_capture_proxy(tree_node*)

The problem in both tests is that is_capture_proxy thinks your
__func__ VAR_DECL with DECL_VALUE_EXPR is a capture proxy, since it is
neither an anonymous union proxy nor a structured binding.

The standard says,

The function-local predefined variable __func__ is defined as if a
definition of the form
   static const char __func__[] = "function-name ";
had been provided, where function-name is an implementation-defined
string. It is unspecified whether such a variable has an address
distinct from that of any other object in the program.

So changing the type of __func__ (from array to pointer) still breaks
conformance.  And we need to keep the type checks from pretty4.C, even
though the checks for strings being distinct need to go.

Jason