Re: A few simple DImode improvements

[Richard Henderson <rth@redhat.com>]

On 06/28/2010 11:33 AM, Jeff Law wrote:
> On 06/28/10 12:05, Ian Lance Taylor wrote:
>> I don't know
>> whether this a concern with IRA; can IRA allocate a DImode pseudo to a
>> floating point register if there are SImode SUBREGs of it?  The old
>> register allocator wouldn't, and you could wind up with a bunch of
>> reloads.
>>    
> I would expect that unless the target explicitly forbids such an
> allocation via CANNOT_CHANGE_MODE_CLASS, then it ought to work.  In
> fact, this is a normal code generation situation for the PA family to
> support xmpyu -- if it had been broken I suspect we would have heard
> about it by now as anything doing an integer multiply would suddenly be
> using libcalls instead of xmpyu.

CANNOT_CHANGE_MODE_CLASS is the normal state of affairs for several
ports doing int<->fp conversion.  Where DImode is the only valid
integer mode, and the single-precision load instruction does some
bit swizzling (to place the SFmode value into register format) so
that 32-bit integer values cannot be loaded or manipulated.

This is true of some ppc variants and alpha, at least.  As such,
this is sort-of a non-answer, Jeff.  


r~