Re: [PR51752] publication safety violations in loop invariant motion pass

[Aldy Hernandez <aldyh at redhat dot com>]

> Ok. I see.  So, I think what would be best is to have a way to check whether
> a store/load is part of a transaction - do we have a way to do that right now?
> (For example a flag on a gimple stmt?)  Then we can simply avoid the LIM

We do not (*).  My patch accumulates that information on demand.  I can 
certainly add a gimple bit for this, but can't the optimizations 
change/rewrite the stores/loads so we lose this information?

> transform by making transaction load/store stmts behave the same as
> potentially trapping stmts (thus, only optimize if the memory is accessed
> unconditional somewhere else).  That would work for PRE as well.
> [easiest would be to make *_could_trap_p return true for memory ops
> inside a transaction]

Provided the gimple bit works, this seems reasonable, though quite a big 
hammer.  But given that we are nearing a release, I would be in favor of it.

Richard Henderson, what do you think?

Aldy

(*) Well technically we do, but much later in the tmmark pass, when we 
instrument the loads, but this is useless since all the tree optimizers 
have been run (loop IM, etc).