🚀 go-pugleaf

In article <lgnojjINN627@exodus.Eng.Sun.COM> tremblay@flayout.Eng.Sun.COM (Marc Tremblay) writes:

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>>   Any conditional branch over
>>   a short sequence of instructions was optimised into a short
>>   sequence of conditionally-executed instructions, which reduced
>>   the code size and saved flushing the pipeline (there was no smart
>>   branch prediction or delayed branches).
>
>The last sentence is key here. If branches can be predicted with decent
>accuracy then it is hard to obtain benefits from conditional moves
>over using conditional branches. 

Do you have any data to back up this claim?

Don't forget that conditional move sequences can be shorter than the 
corresponding branch sequence.  In other words, the two instruction
sequence branch/op can sometimes be replaced with a single conditional move 
instruction.

Second, I believe the second order effect of providing larger basic blocks
is the conditional move's greatest benefit.  Larger basic blocks offer
more scheduling opportunities.  I don't have any data (yet), but I've 
certainly seen it happen.

-- 
Andrew C. Payne
DEC Cambridge Research Lab