Re: [Patch, AVR]: Fix PR46779

[Georg-Johann Lay <avr@gjlay.de>]

Georg-Johann Lay schrieb:
> Denis Chertykov schrieb:
> 
>>2011/6/9 Georg-Johann Lay <avr@gjlay.de>:
>>
>>>This is a tentative patch to fix PR46779 and hopefully also related
>>>issues like PR45291.
>>>
>>
>>-  /* Disallow QImode in stack pointer regs.  */
>>-  if ((regno == REG_SP || regno == (REG_SP + 1)) && mode == QImode)
>>+  /* Don't allocate data to non-GENERAL_REGS registers.  */
>>+
>>+  if (regno >= 32)
>>     return 0;
>>
>>I think that we not need in this code.
>>GCC core must bother about this.
> 
> 
> I am unsure about that. There is the "q" constraint that is used for
> SP. register_operand will accept SP because regno_reg_class does not
> return NO_REGS for SP. So something must stop the register allocator
> from allocating ordinary data to SP.
> 
> In the current md there is "*movhi_sp" insn prior to "*movhi" insn.
> Besides that it is strongly discouraged to have more than one move
> insn for one mode, not each and every place looks at insn conditions.
> 
> Moreover, if there is an insn like
> (set (reg:HI 100)
>      (reg:HI 101))
> that matches "*movhi", what will keep IRA from allocating one of the
> values to SP, i.e. chose alternative "q,r" or "r,q"?

Ok, SP is a fixed register, I missed that above :-)

For the "*movhi_sp" I will provide a patch too as soon as I find the time.

Johann