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Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."

From: Scott Robert Ladd
Subject: Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
Date: Fri, 29 Dec 2006 16:28:09 -0500
User-agent: Thunderbird (Windows/20061207)

Ian Lance Taylor wrote:
I fully appreciate that there is a real problem here which needs to be
addressed, but this does not seem like the best solution to me.  A
great number of C programs are built using autoconf.  If we make this
change, then they will all be built with -fwrapv.  That will disable
useful loop optimizations, optimizations which are enabled by default
by gcc's competitors.  The result will be to make gcc look worse than
it is.

The inclusion of -fwrapv is a good idea from the standpoint of producing reliable code; it is a bad idea from the point of GCC PR.

Which begs the question: Should GCC care about its PR?

GCC suffers from many misconceptions due to its complexity. When it comes to code optimization, GCC offers more options than any other compiler I know. Literally hundreds of options combine in sometimes surprising ways, allowing a knowledgeable GCC user to fine-tune their code generation.

Back in the "old days", GCC was only used by expert UNIX hackers who were educated about their tools. Today, GCC is being used by a more general audience to develop consumer code. As such, GCC needs to err on the side of reliability and backward compatibility, benchmarks be damned.

So if adding -fwrapv to autoconf keeps the current GCC from breaking existing code at the cost of some speed, that's a Good Thing. Vendors and Gentoo users who really care about performance can manually set flags to boost their performance.

I don't want to see GCC "dumbed down" -- experts need a compiler with this sort of fine-tuned power.


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