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

[Scott Robert Ladd]

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.

..Scott