[LLVMdev] A small pass to constant fold branch conditions in destination blocks

[Duncan Sands]

>>> While I know PS removed tons of code from the .ll I was never really
>>> able to detect a runtime performance improvement; my guess is that while
>>> I was killing off lots of dead code it didn't impact the performance of
>>> the live code much or at all.
>>>
>>
>> Killing off lots of dead code is going to improve compile time,
>> since code-gen time tends to dominate optimise time.
>>
>> Improving compile time is important for those of us using the JIT compiler.
>
> Except PredSimplify was also a big compile time sink, and didn't make up for any benefits it gave on that front.

A big advantage of my pass is that it seems to be pretty quick.  That's because
it doesn't try to go beyond simple propagation of equalities.

Ciao, Duncan.