[Bug c/56977] gcc -Og incorrectly warns about 'constant zero length parameter'

[harald at gigawatt dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56977

Harald van Dijk <harald at gigawatt dot nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |harald at gigawatt dot nl

--- Comment #1 from Harald van Dijk <harald at gigawatt dot nl> ---
This is a bigger problem with glibc's open() implementation, where correct use
does not just lead to a warning, but to a compile-time error. Self-contained
test:

__attribute__((__error__("error"))) void error ();

void f (int);

extern inline __attribute__((__always_inline__)) void f (int i) {
  if (__builtin_constant_p (i)) {
    error ();
  }
}

void g(int j) {
  f (j);
}

Compiling with -Og leads to:

$ gcc -Og -c test.c
In function ‘f’,
    inlined from ‘g’ at test.c:12:5:
test.c:7:11: error: call to ‘error’ declared with attribute error: error
     error ();
           ^
$ gcc --version
gcc (GCC) 4.8.1 20130603 (Red Hat 4.8.1-1)
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

The if block, including the call to error(), gets removed at all optimization
levels (even -O0) other than -Og.