http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51165
--- Comment #6 from rguenther at suse dot de <rguenther at suse dot de> 2012-01-11 15:13:39 UTC --- On Wed, 11 Jan 2012, aldyh at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51165 > > Aldy Hernandez <aldyh at gcc dot gnu.org> changed: > > What |Removed |Added > ---------------------------------------------------------------------------- > CC| |rguenth at gcc dot gnu.org, > | |rth at gcc dot gnu.org > > --- Comment #5 from Aldy Hernandez <aldyh at gcc dot gnu.org> 2012-01-11 > 15:07:15 UTC --- > The main problem here is that we are using ptr_deref_may_alias_global_p() to > determine if a dereferenced address escapes whereas we were previously using > is_call_clobbered() which understood VAR_DECLs, not just SSA_NAMEs. > > In requires_barrier() we call ptr_deref_may_alias_global_p() to determine if > the address of `lala' below will escape: > > struct large { int x[100]; }; > extern struct large foobie (void) __attribute__((transaction_safe)); > int asdf; > > int f() > { > struct large lala; > struct large lacopy = foobie(); > __transaction_atomic { > lala = lacopy; <-- STORE SHOULD BE TRXN/THREAD LOCAL > } > return lala.x[asdf]; > } > > Before the fix to PR tree-optimization/43572, we used is_call_clobbered() > which > returned false for `lala', and everything worked fine. However, we are now > using ptr_deref_may_alias_global_p() which only understands SSA_NAMEs, and > `lala' is a VAR_DECL. > > Mr. Guenther (or Mr. Henderson), what is the recommended course of action > here? If you want to check whether something possibly escaped you can use may_be_aliased (get_base_address (xxxx)) and if xxx is always a VAR_DECL you can omit get_base_address. If get_base_addres (xxxx) returns a MEM_REF you can refine the result by calling ptr_deref_may_alias_global_p on its operand 0 (the pointer to the object). There is no existing predicate that would answer whether a tree accesses possibly 'escaped' memory (yet). If you write one, stick it into tree-ssa-alias.c. Richard.
