Re: Extending constraints using register subclasses

[Jim Wilson <wilson at codesourcery dot com>]

Jamie Prescott wrote:
> enum reg_class
> {
>         NO_REGS = 0,
>         GENERAL_REGS,
>         X_REGS,
>         R0_REG, R1_REG, R2_REG, R3_REG,

The only obvious thing I notice is that you have the largest classes 
first.  The docs say to put the smaller classes first.  The compiler 
always assumes that if a register matches more than one class, then the 
class with the lowest number is the smallest one (most specific one). 
This matters when looking for the smallest matching class.

In tm.texi, REGISTER CLASSES, it says
> Order the classes so that if class @var{x} is contained in class @var{y}
> then @var{x} has a lower class number than @var{y}.

Otherwise, you should try to debug this a little.  The place in 
reload1.c where the error message is printed isn't hard to find.  Put a 
break point before the constrain_operands call.  Check to see if the 
instruction was reloaded correctly, or if constrain_operands is failing. 
 If the failure is in constrain_operands, then it shouldn't be too hard 
to find the problem.  If the insn rtl is wrong, then this will take some 
work to figure out where it went wrong.

Jim