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Re: [Qemu-devel] Re: Performances on Mac OS X

From: Fabrice Bellard
Subject: Re: [Qemu-devel] Re: Performances on Mac OS X
Date: Wed, 04 Aug 2004 22:56:30 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030624

Don't spend your time in using another compiler than gcc : most of the time is spent in the generated code, and the quality of this code relies on very small functions which are too simple for being optimized better.


Roine Gustafsson wrote:
Joshua Root address@hidden wrote:

Laurent Amon <address@hidden> wrote:

I was wondering whether the implementation of qemu is tied to gcc or
if it might
be interesting to try to compile using IBM's compiler, which is able to generate
Altivec code...

I have tried compiling qemu with xlc and it chokes on the asm. I believe that it uses a different syntax than gcc for this. I don't know what its syntax is, but if anybody does it shouldn't be too hard to make a patch which lets it compile.

Using xlc does seem to give substantially better performance than gcc, and not just on floating point code.

xlc is picky with the source and takes FOREVER to compile with -O6. However,
xlc is object compatible with gcc, so usually you just use xlc on core stuff
that needs the speed, and gcc for everything else.
Compile everything with gcc, rm the object files you want to remake with xlc
(based on profiling), edit the makefiles to use xlc and make again.

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