[RTL, i386] Use subreg instead of UNSPEC_CAST

Richard Henderson rth@redhat.com
Wed Mar 20 15:13:00 GMT 2013

On 03/20/2013 08:00 AM, Marc Glisse wrote:
> Do you at least agree that vector-vector subregs make sense, or is that part
> wrong as well?

You mean a V4SImode subreg of a V8SImode register, not just same-size casting?
It makes logical sense, but I'm fairly sure you'll need a lot more surgery
throughout the compiler to make that happen.

I'm curious how a define_expand can fail in LRA, but your define_insn succeeds?
Is the failure because of ix86_cannot_change_mode_class?  Because that hook
fairly well defines what subregs are valid.  And if that says it isn't valid,
then even having a define_insn that uses such is wrong.


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