Re: [trans-mem] make alias oracle understand TM read/writes

[Richard Henderson <rth at redhat dot com>]

On 08/31/2009 02:30 PM, Richard Guenther wrote:
> I see that pass_tm_mark is run right before expansion - so you only
> need it to have points-to information on RTL working.  Is there any
> reason you lower TM so late?

The implementation of TM adds edges from each TM read/write function 
back to the start of the transaction, so as to model the transaction 
restart that the library may force.  However, modeling this is only 
required at the rtl level, since the only thing that is affected by this 
restart are hard registers.

At the gimple level a model in which the entire transaction occurs, or 
none of it occurs (i.e. transaction abort), is correct and is 
significantly easier for the optimizers to cope with.

> Note that if we ever get IPA PTA working
> everything that re-computes points-to information after it will
> likely scrap IPA points-to information.

Is it your contention, then, that we do not need to re-compute alias 
information at all, if we're merely making local substitutions? 
Frankly, I've lost track of how alias information actually works.

It would be like me to tell Aldy to add all the TM builtins to the 
oracle to make sure alias info still works and then find that absolutely 
nothing needed to happen at all...


r~