Re: [PATCH] Don’t use AC_EGREP_CPP if affected by CFLAGS

[Paul Eggert]

On 11/06/2017 11:23 AM, Bruno Haible wrote:
> When the error rate is so high, we should
>    1) improve the documentation (this is mainly install.texi from Autoconf),
>    2) add a consistency check in AC_PROG_CC or AC_PROG_CPP.
(2) would be better than what we have now, yes. But how could such a 
check be implemented robustly? Wouldn't it require a comprehensive 
knowledge of which compiler options affect which predefined macros on 
which platforms?

The problem is not limited to flags like -m32 and -m64. Flags like 
-fsanitize=address can also affect preprocessor behavior. A complete 
list of such flags would be daunting to maintain.

In contrast, it's relatively simple to say "Don't use AC_EGREP_CPP 
unless you know the result isn't likely to depend on compiler options."