i386/x86-64 UNSPEC_NOP usage

[Jim Wilson]

Jan Beulich wrote:
> Would you be able to explain what UNSPEC_NOP is really good for.

Try deleting it and see what breaks.

Since the comments refer to combine cleverness, and the affected 
patterns are mostly DImode/TImode ones, I assume the problem is that the 
optimizer does not know much about how to optimize vector modes, but it 
does know how to optimize integer modes.  So perhaps our carefully 
crafted mmx DImode patterns are being rewritten in ways that prevent us 
from later emitting the mms/sse instructions we want.  Or maybe mmx 
instructions are being created where we don't want them.

 > While I'm trying
 > to fix various inconsistencies in the MMX/SSE support, I'd like to also
 > do away with some of the superfluous builtins.

Superfluous how?  Just because there are builtins that are not useful to 
users does not mean they can be eliminated.  If there is a standard, or 
a reference compiler (e.g. icc) that has them, then we need them also, 
even if they aren't really needed by end users.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com