[C PATCH] Warn about unused RHS of COMPOUND_EXPR (PR c/59871)

[Marek Polacek]

On Tue, Jan 21, 2014 at 09:18:17PM +0100, Marc Glisse wrote:
> On Tue, 21 Jan 2014, Marek Polacek wrote:
> 
> >--- gcc/libdecnumber/decNumberLocal.h.mp	2014-01-21 18:34:32.235540589 +0100
> >+++ gcc/libdecnumber/decNumberLocal.h	2014-01-21 19:04:12.173243034 +0100
> >@@ -155,8 +155,10 @@ see the files COPYING3 and COPYING.RUNTI
> >  /* Store a uInt, etc., into bytes starting at a char* or uByte*.    */
> >  /* Returns i, evaluated, for convenience; has to use uiwork because */
> >  /* i may be an expression.					      */
> >-  #define UBFROMUS(b, i)  (uswork=(i), memcpy(b, (void *)&uswork, 2), uswork)
> >-  #define UBFROMUI(b, i)  (uiwork=(i), memcpy(b, (void *)&uiwork, 4), uiwork)
> >+  #define UBFROMUS(b, i)  (uswork=(i), memcpy(b, (void *)&uswork, 2), \
> >+			   (void)uswork)
> >+  #define UBFROMUI(b, i)  (uiwork=(i), memcpy(b, (void *)&uiwork, 4), \
> >+			   (void)uiwork)
> 
> This looks wrong to me. The comment before says that those macros
> "return" uiwork, so you can't cast it to void in the macro. Options:
> 
> 1) cast to void in the users of the macro:
> (void) UBFROMUS(acc+4, 0);
> 
> 2) Make the macros not return (since none of the users use the
> return value), i.e. remove ", uiwork" at the end and update the
> comment before. (you may need to cast the return of memcpy to void,
> which makes more sense)

I went with 2).  Still it looks kind of weird, but I don't care enough as long
as it bootstraps ;).  I'll post a patch once the regtesting finishes.
Thanks.

	Marek