Re: [PATCH 1/* v3] Generic string function optimization: Add skeleton

[OndÅej BÃlka <neleai at seznam dot cz>]

On Fri, May 29, 2015 at 10:42:17AM +0000, Joseph Myers wrote:
> On Fri, 29 May 2015, OndÅej BÃlka wrote:
> 
> > On Thu, May 28, 2015 at 08:54:31PM +0000, Joseph Myers wrote:
> > > On Thu, 28 May 2015, OndÅej BÃlka wrote:
> > > 
> > > > Both comments are correct. We should do it generically and surround
> > > > these functions with ifdef to supply arch-specific versions. 
> > > 
> > > #if, not #ifdef, please, for all architecture choices in these functions.  
> > > The sysdeps/generic version of the header architectures can use to change 
> > > the default choices should have detailed comments on the default 
> > > definitions of all the relevant macros to explain their semantics.
> > > 
> > For what purpose? Its pointless except that you would need to have
> > additional header say precommon.h, then undef and redefine macro when
> > you want change.
> 
> The general principle is that macro uses should be typo-proof.  That means 
> avoiding #ifdef, #ifndef and #undef where possible.
> 
> The principle of documenting macro semantics applies even if there's a 
> good reason typo-proof conventions are problematic in a particular case.  
> There should *never* be any sort of architecture hook without clear 
> documentation of the semantics of the hook (written from the perspective 
> of an architecture maintainer wanting to know how to set the hook for 
> their architecture, not from the perspective of the person writing the 
> code using the hook).  I always advise writing documentation early in the 
> process of developing a patch - the documentation is as important as the 
> rest of the code.
> 
> > And it doesn't help to catch any errors. If you misspell define then you
> > will get error with duplicate definition.
> 
> If the code does
> 
> #ifdef MACRO
> 
> or
> 
> #ifndef MACRO
> 
> then if an architecture does
> 
> #define MCARO
> 
> (with or without #undef) that will silently be ignored.
> 
> If, instead, the code does
> 
> #if MACRO
> 
> and there's a sysdeps/generic header that defines MACRO one way, if an 
> architecture overrides that header with one that misspells the name, a 
> -Wundef warning will be immediately visible (though we still need to fix 
> the -Wundef warnings in the testsuite and remove the -Wno-error=undef).
> 
Joseph, read previous mail before writing. Your suggestion is pointless.

For a code

#ifndef CUSTOM_FOO
int foo()
{
}
#endif

If architecture does
#define CUTSOM_FOO
int foo()
{
}

Then it gets error with redefinition of foo.