Re: Add macros for diagnostic control, use them in locale/weightwc.h

[Paul Eggert <eggert@cs.ucla.edu>]

On 11/18/2014 01:18 PM, Roland McGrath wrote:
> We should only ever disable warnings with the
> tightest possible scope around where we know for sure we need to.

In that case neither my patch nor Joseph's should be accepted.  If I 
understand Joseph's patch correctly,the maybe-uninitialized warning 
needs to be disabled only when dereferencing'cp'.  For example, in the 
expression 'cp[cnt]', the warning should be disabled only for the load 
from 'cp[cnt]'; it should not be disabled for the load from 'cp' itself, 
or for the load from 'cnt'.  So Joseph's proposed patch doesn't have a 
tight scope here.  It should be possible to tighten itto cover only the 
places where troublesome dereferences actually occur, e.g., by defining 
a macro 'NO_MAYBE_UNINITIALIZED_DEREFERENCE (p)' that suppresses the 
warning while dereferencing the pointer P, by using 
'NO_MAYBE_UNINITIALIZED_DEREFERENCE (cp + cnt)' in place of 'cp[cnt]', etc.

Also, as I understand it the warning should be disabled only on x86-64, 
and only if optimization is enabled, as we don't know of problems with 
other platforms or when optimization is turned off.

There may be other ways to tighten the scope, too.

However, I'm still not convinced that it's worth the trouble to insist 
on tight scopes like this.  Many of these bogus warnings are due to 
compiler bugs; I'm afraid we've seen this too often in gnulib, when 
supporting projects that use -Werror.  If we start worrying about tight 
scopes for workarounds for GCC cry-wolf bugs, we will too easily go down 
the rabbit hole of maintaining a fragile and evolving list of GCC 
compiler bugs rather than maintaining glibc.