Re: [PATCH] libcpp: suppress builtin macro redefined warnings for __LINE__

[Joseph Myers <joseph@codesourcery.com>]

On Fri, 2 Dec 2022, Longjun Luo via Gcc-patches wrote:

> 
> On 12/2/2022 1:01 AM, Joseph Myers wrote:
> > On Thu, 1 Dec 2022, Longjun Luo via Gcc-patches wrote:
> > 
> > > diff --git a/gcc/testsuite/gcc.dg/builtin-redefine.c
> > > b/gcc/testsuite/gcc.dg/builtin-redefine.c
> > > index 882b2210992..9d5b42252ee 100644
> > > --- a/gcc/testsuite/gcc.dg/builtin-redefine.c
> > > +++ b/gcc/testsuite/gcc.dg/builtin-redefine.c
> > > @@ -71,7 +71,6 @@
> > >   /* { dg-bogus "Expected built-in is not defined" "" { target *-*-* } .-1
> > > } */
> > >   #endif
> > >   -#define __LINE__ 0           /* { dg-warning "-:\"__LINE__\" redef" }
> > > */
> > >   #define __INCLUDE_LEVEL__ 0  /* { dg-warning "-:\"__INCLUDE_LEVEL__\"
> > > redef" } */
> > >   #define __COUNTER__ 0        /* { dg-warning "-:\"__COUNTER__\" redef" }
> > > */
> > Is there some existing test that verifies that this redefinition is still
> > diagnosed by default (in the absence of -Wno-builtin-macro-redefined)?
> 
> I am not sure I have fully understood your meaning. The problem here is that
> if I try to redefine __LINE__ macro in the situation that projects use the
> option '-Werror', the compile will fail.

There are two cases:

(a) Is redefinition of __LINE__ diagnosed *without* 
-Wno-builtin-macro-redefined?

(b) Is redefinition of __LINE__ diagnosed *with* 
-Wno-builtin-macro-redefined?

My understanding is that both (a) and (b) have answer "yes" at present, 
and your patch would change the answer to (b) to "no", without changing 
the answer to (a).

My question is about whether there is a test verifying the answer to (a).  
If not, I think the patch should add one.

-- 
Joseph S. Myers
joseph@codesourcery.com