[Bug other/39347] Vector mode class for CCmode is missing

["amylaar at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from amylaar at gcc dot gnu dot org  2009-03-02 18:59 -------
(In reply to comment #3)
> I still don't understand what you mean by that.  Do you mean the registers are
> vector based and the instructions effect the conditional register and that
> conditional register has slots (elements) that correspond to the vector slots
> (elements)?

Exactly.  The conditiona register is known as V8CCImode
for ordinary integer instructions, V8CCZNmode if only N/Z flags matter,
and V8CCZmode when only the Z falg is relevant.  You can copy it from/to
a general purpose vector register, in which case it looks like a V8PHImode
register with 6 valid bits per element.

There are also use cases where it acts as having 32 bit partial elements.

>  Still having a vector mode of CCmode seems weird.

Actually, it makes more sense than a scalar CCmode register.
The limited clock frequency is compensated for by higher throughput
per cycle.

Van Neumann would have said that having a processor with 4 or 5 different
types of physical memory (L1 Dcache, L1 Icache, L2 cache, maybe L3 cache,
main memory) seems weird.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39347