Re: Problem with address reloading

[Jim Wilson <wilson at specifix dot com>]

Juul Vanderspek wrote:
> In order to enable indexed loads, I extended
> GO_IF_LEGITIMATE_ADDRESS to also match indexed
> addresses, added a memory constraint 'R' to match
> nonindexed addresses, and used R for stores in the
> 'mov' rule (see below).

This may be easier if you do it the other way.  I.e. remove indexed 
addresses from GO_IF_LEGITIMATE_ADDRESS, add an 'R' constraint that only 
matches indexed addresses, and then use "mR" for load memory operands, 
and "m" for store memory operands.  With a proper predicate for 
input_operands that accepts memory_operand plus indexed addresses, 
combine can create the indexed loads.

It should be possible to make your approach work.  First thing is that 
you have to fix the predicate.  You can't use nonimmediate_operand here, 
as this will accept invalid indexed addresses.  Define your own 
output_operand predicate that rejects indexed addresses.  It is always 
better to reject an operand than to rely on reload to fix it.  You 
probably also need a mov* expander that fixes a store indexed address if 
one is passed in, since it is a bad idea for the mov* patterns to fail.

Another problem here is that reload knows how to fix simple things like 
'm' and 'r' operands, but it doesn't know how to fix an 'R' operand. 
This means you either have to be careful to only accept operands that 
will never be reloading, or add code to reload it yourself, or add hints 
to help reload.  The last one is the easiest option, see the 
EXTRA_MEMORY_CONSTRAINT documentation.  If you define this, then reload 
will know that it can always fix an 'R' by reloading the address into a 
register.
--
Jim Wilson, GNU Tools Support, http://www.specifix.com