Expanding instructions with condition codes inter-deps

Paulo J. Matos paulo@matos-sorge.com
Tue Oct 18 13:44:00 GMT 2011

On 17/10/11 17:20, Andrew Pinski wrote:
> On Mon, Oct 17, 2011 at 3:50 AM, Paulo J. Matos<paulo@matos-sorge.com>  wrote:
>> addc_internal looks like:
>> (define_insn "addc_internal"
>>   [(set (match_operand:QI 0 "nonimmediate_operand" "=c")
>>         (plus:QI
>>           (plus:QI
>>             (ltu:QI (reg:CC RCC) (const_int 0))
>>             (match_operand:QI 1 "nonimmediate_operand" "%0"))
>>           (match_operand:QI 2 "general_operand" "cwmi")))
>>    (clobber (reg:CC RCC))]
>>   ""
>>   "addc\\t%0,%f2")
> Try adding (use (reg:CC RCC)) to the pattern above.

Currently compiling that change into the code. I have a feeling that it 
will either confuse compare-elim.c or that it will be too strict and 
remove any possibility of optimization since with (use (reg:CC RCC)) we 
are not really saying that we are only interested in the carry flag 
instead of the whole thing. It will avoid anything clobbering RCC which 
is most of the instructions.

I will give it a spin and see what actually happens.



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