Re: [sdcc-devel] Optimal register allocator for hc08

[Philipp K. K. <pk...@sp...>]

Am 14.04.2012 07:48, schrieb Erik Petrich:
> 
> 
> On Fri, 13 Apr 2012, Philipp Klaus Krause wrote:
> 
>> I just commited revision #7585. Everything compiles, code looks much
>> better now, and all current failures are in the library, not the tests
>> themselves (13 tests are failing).
> 
> As of revision #7586, there are no regression test failures.

Thanks a lot!. There's one more issue I don't see clearly: When removing
the comments at

/*if(ic->op == RECEIVE && (!ic->next || !(ic->next->op == RECEIVE) ||
!result_in_X || getSize(operandType(result)) >= 2))
    return(true);*/

in ralloc2.cc, I get some regression failures. I looked at the diff in
the asm generated, but couldn't see the problem. A typical one
(gcc-torture-execute_compare-3) is attached.


> 
>> I wonder if it would be a good idea to allow more register combinations,
>> e.g. AX and AH. It should be easy to make instructions that don't care
>> about the order, like assignment and cast to accept them as input.
>> Furthermore they are cheap to emit as result by arithmetic instructions
>> (since the highest byte is calculated last and already in a at the end
>> of the instruction).
> 
> I'm still not very convinced of the usefulness of H in any context other 
> than HX. The only place I see that it might be useful is with the DIV 
> (divide) instruction; it uses HA as the dividend and leaves the remainder 
> in H. But the complications don't seem to me to be worth the payoff.
> 
> On the other hand, I think AX could be useful, particularly for 
> shifts/additions leading to a pointer get/set (which requires the address 
> in HX, so we only need to transfer A to H).

OK, so I'll try to enable AX later this week.

Philipp