[llvm-commits] patch: CXAGuardElimination pass.

[Duncan Sands]

Hi Nick,

>> What about this:
>>
>> bb1: acquire
>>       br bbr
>> bb2: acquire
>>       br bbr
>> bbr: release
>>
>> Aren't you going to eliminate the first acquire and the release, but
>> not the second acquire?
> 
> No, it'll eliminate the second acquire and the release, but not the 
> first acquire. Note that there's code to detect this case in 
> deadGuardElim (see the comments).

note that bb1 doesn't branch to bb2, it branches to bbr.

> As far as I can tell that's valid behaviour for this transform so long 
> as we don't mind removing infinite loops (note that these infinite loops 
> can't be deliberately constructed by the user code, the calls to 
> __cxa_guard are always emitted by the compiler...).

Not sure what you are saying?  I hope you are not saying that this
transform relies on a particular style of guard usage being fed into
it...

Ciao,

Duncan.