Re: [PATCH] Fix PR c/12446

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

Eric Botcazou <ebotcazou@libertysurf.fr> writes:

| Hi,
| 
| This is a (minor) regression from GCC 3.0.4 present on 3.3 branch and 
| mainline, introduced by this patch:
|    
|    http://gcc.gnu.org/ml/gcc-patches/2001-11/msg00319.html
| 
| Before the patch, GCC emitted "error: invalid use of non-lvalue array" for
| 
|    struct s { char c[1]; };
| 
|    extern struct s foo(void);
| 
|    void bar(void)
|    {
|      char *ptr = foo().c;
|    }
| 
| in C90 mode. After, it ICEs when trying to expand a BLKmode move.
| 
| 
| The patch added the comment
| 
| /* Before C99, non-lvalue arrays do not decay to pointers.
| +  Normally, using such an array would be invalid; but it can
| +  be used correctly inside sizeof or as a statement expression.
| +  Thus, do not give an error here; an error will result later.  */

More precisely, before C99, it was undefined behaviour if a program
needs a non-lvalue array to decay to a pointer.  Apparently, GCC
chosed to  error out.  It could also have chosen to accept the
construct with some warning.  In effect, since the construct is now
explicitly valid in C99, I would rather we accept the construct with a
warning, or reject the construct only if -pedantic and std=c90.
At nay rate, I believe your comment should be updated to reflect the
fact that it is an juridiction area left to the compiler.

-- Gaby