AW: C and C++ parser performing optimizations

["Stefan Franke" <stefan@franke.ms>]

> -----Ursprüngliche Nachricht-----
> Von: Alexander Monakov <amonakov@ispras.ru>
> Gesendet: Sonntag, 2. August 2020 20:41
> An: Stefan Franke <stefan@franke.ms>
> Cc: gcc-help@gcc.gnu.org
> Betreff: Re: C and C++ parser performing optimizations
> 
> On Sun, 2 Aug 2020, Stefan Franke wrote:
> 
> > So the parser performs unwanted and uncontrollable optimizations,
> > which I consider bogus.
> 
> On occasion they are also incorrect.
> 
> My (possibly wrong or incomplete) understanding is that GCC does not have
> internal separation of mandatory simplifications that need to be done in
the
> frontend (like constant folding in the context of integer constant
> expressions) vs. optional simplifications (optimizing substitutions).
> So it just does both at the same time.
> 
> Alexander

Here is an example where gcc creates wrong code:

test.c:
int foo() {
  const char * const txt = "hello";
  register const char * const p asm("ecx") = txt;
  register int dx asm("edx");
  asm(" call _faa" :"=r" (dx) :"rf" (p));
}

gcc -O1 -S test.c -fdump-tree-original

The variable p gets replaced and the asm input parameters are wrong:

__asm__(" call _faa":"=r" dx:"rf" (const char * const) "hello");

Uh - oh!

Stefan