Re: reload in incompatible constraints

[Ian Lance Taylor <iant@google.com>]

Aurelien Buhrig <aurelien.buhrig.gcc@gmail.com> writes:

> 2011/6/28 Ian Lance Taylor <iant@google.com>:
>> Aurelien Buhrig <aurelien.buhrig.gcc@gmail.com> writes:
>>
>>> I'm trying to implement TARGET_SECONDARY_RELOAD but I cannot make it
>>> work properly.
>>> The hook seems to work for preventing from moving from BASE_REG to
>>> BASE_REG in HImode by inserting a GENERAL_REG.
>>> But I also want to insert a GENERAL_REGS intermediate register when
>>> moving between BASE_REGS registers and memory in HImode.
>>>
>>> So I wrote something like that in my TARGET_SECONDARY_RELOAD:
>>> if (MEM_P(x) && (reload_mode == HImode) && reload_class == BASE_REGS)
>>>      return GENERAL_REGS;
>>>
>>>
>>> But it seems this do not work. For instance with DI function parameter
>>> access (movdi reg:DI <-- m) which are (automatically) split into movhi
>>> subreg:HI <-- m; then in movhi reg:HI <- m. But the hook do not seem
>>> to work since the reg:HI is reloaded into a BASE_REG...
>>>
>>> So when is this hook called? Is there something specific with spliting
>>> insn? Or just a general thing about TARGET_SECONDARY_RELOAD I missed ?
>>
>> The hook is called during reload, which is run as part of register
>> allocation.  When are you splitting the DImode load?
>>
>> Ian
>>
> I have no instruction for it. GCC automatically splits it, and it does
> it at the very beginning (131r.expand) by affecting a subreg:HI, and
> affects a reg:HI at 139r.subregs, and a hard base_reg at 176r.greg. It
> is never changed after.
>
> Would it be a reg class pb ?
> For now, I defined BASE_REGS class for address registers which does
> not intersect with GENERAL_REGS class (the data registers). Should I
> define Address register and data register as general register, with a
> class for address register and a new class for data registers (such as
> m68k) ?
>
> Does GCC treat GENERALS_REGS differently than other classes ?

Yes, but I don't see why this would be your problem.

From your description I don't know why this is not working.  You are
going to have to debug it.  Probably the first thing to try would be a
few debug statements in your TARGET_SECONDARY_RELOAD to see if it is
being invoked as you expect.

Ian