[Bug c/67661] Wrong warning when declare VLAs: operation on 'x' may be undefined [-Wsequence-point]

[leechung at 126 dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67661

--- Comment #2 from leechung  ---
(In reply to jos...@codesourcery.com from comment #1)
> You'll need to give a full testcase (complete compilable file and options 
> used to compile it).  What you gave isn't a compilable testcase; it gives 
> "error: variably modified 'y' at file scope".  Put inside a function, it 
> gives "warning: unused variable 'y' [-Wunused-variable]", but does not 
> give the warning you mention.  And there's no variable 'b' in your example 
> at all.

Sorry, I am less experience.
The following is the complete code:

#include 

int main (void)
{
int x = 0, y [++ x], z [++ x];
printf ("%d, %d, %d\n", sizeof x, sizeof y, sizeof z);
return 0;
}

and are compiled with option '-Wall'.for example:
gcc xx.c -Wall

then produce a warning 'operation on 'x' may be undefined [-Wsequence-point]'

[Bug c/67661] New: Wrong warning when declare VLAs: operation on 'b' may be undefined [-Wsequence-point]

[leechung at 126 dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67661

Bug ID: 67661
   Summary: Wrong warning when declare VLAs: operation on 'b' may
be undefined [-Wsequence-point]
   Product: gcc
   Version: 5.2.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
  Assignee: unassigned at gcc dot gnu.org
  Reporter: leechung at 126 dot com
  Target Milestone: ---

The following code produces a warning: operation on 'b' may be
undefined.[-Wsequence-point]

int x = 0, y [++ x], z [++ x];

But N1570 6.8 says:
A block allows a set of declarations and statements to be grouped into one
syntactic unit. The initializers of objects that have automatic storage
duration, and the variable length array declarators of ordinary identifiers
with block scope, are evaluated and the values are stored in the objects
(including storing an indeterminate value in objects without an initializer)
each time the declaration is reached in the order of execution, as if it were a
statement, and within each declaration in the order that declarators appear.

and 6.7.6 says:
A full declarator is a declarator that is not part of another declarator. The
end of a full declarator is a sequence point.