Re: Coloring problem - Pass 0 for finding allocno costs

[Jeff Law <law at redhat dot com>]

On 03/18/10 08:30, Frank Isamov wrote:
>  From the h file:
>
> #define REG_CLASS_CONTENTS                                              \
>   {
>              \
>     {0x00000000, 0x00000000, 0x00000000}, /* NO_REGS*/          \
>     {0xFFFFFFFF, 0x0000FFFF, 0x00000000}, /* D_REGS*/          \
>     {0x00000000, 0xFFFF0000, 0x0000FFFF}, /* R_REGS*/           \
>
> ABI requires use of R registers for arguments and return value. Other
> than that all of these instructions are more or less symmetrical in
> sense of using D or R. So, an optimal choice would be use of R for
> this example. And if D register is chosen, it involves additional copy
> from R to D and back to R.
>    
Define a union class which includes all the registers in D_REGS and 
R_REGS, then define IRA_COVER_CLASSES to that union class.  When 
register classes are mostly symmetrical, except for stuff like argument 
passing, return values and the like, you usually get better code by 
defining IRA_COVER_CLASSES with a single union class rather than the 
component subclasses.

In fact, if the only reason D & R are separate is calling conventions, 
then I'd just drop them those classes completely and define 
GENERAL_REGISTERS.   You would typically only define separate register 
classes if there are instructions which have to operate on specific 
subsets of the register file.


Jeff