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

From: Paul Eggert
Subject: Re: [PATCH] Don’t use AC_EGREP_CPP if affected by CFLAGS
Date: Mon, 6 Nov 2017 16:08:37 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

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."

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