Re: [patch] require sse3 for fisttp

[Uros Bizjak <ubizjak at gmail dot com>]

Eric Christopher wrote:

> 2006-09-15 Eric Christopher <echristo@apple.com>

> * config/i386/i386.h (TARGET_FISTTP): Depend only on SSE3 and
> 387.


We have discussed this a couple of months ago, where we decided that 
-msse3 should enable fisttp.

However, looking at your patch, I can't see why it should be better than 
current implementation. Currently, fisttp is enabled only when -msse3 is 
selected _or_ -march=nocona is specified. This is IMO the best 
combination that has some logic in it:

a) user specifies -msse3 and (even if it is counter-intuitive), fisttp 
is generated. This is added to follow Intel arch manual.
b) user specifies -march=nocona. As all nocona cores have fisttp, fisttp 
is generated even without -msse3.

The problem might arise for -march=nocona -mno-sse, where fisttp is 
still generated. But since user knows that his code will run only on 
nocona, but he wants to disable sse insn set (IMO this means usage of 
xmm registers), everything should be OK.

Another problem is 64bit -march=k8 -mfpmath=387, where not all k8 
processors have sse3 and fisttp. There is nothing we can do, but expect 
user to provide -msse3 in this case.

I can't see the benefit of having fisttp disabled by default on nocona 
(this is the only target_fisttp target).

Uros.