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Re: GCC 4.1 now the default GCC version for etch

On Tue, Jun 20, 2006 at 12:32:18PM +0200, Goswin von Brederlow wrote:
> Exactly. Isn't the x86_64 instruction set basicaly the same as ia32
> just with a few extra opcodes and more registers? Any general fault in
> the instruction set should still remain.

x86 processors have multiple modes with different instructions and
registers in each mode.  AMD decided to make long mode remove some old
features and in some cases replace them with new features.

If there was a problem with some instruction in previous modes doesn't
mean that they had to keep that fault in the new mode, since the new
mode only applies to any OS that switches the cpu into that mode and
hence knows about the new behaviour.

So goodbye to mmx, and various other crap thigns.  x87 is supported on
current CPUs but there are feature flags that will permit the removal of
x87 support in the future.  Both linux and windows encourage the use of
sse instead of x87 for floating point, and I believe all compilers by
default do so in long mode for all current OSs that support amd64, so
the removal shouldn't be a problem sometime in the future (although
doing so would I suppose prevent running 32bit floating point
applications anymore without recompiling those for sse.)

Len Sorensen

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