On Thu, Nov 1, 2012 at 11:16 AM, Dmitry Vyukov <dvyu...@google.com> wrote: > On Thu, Nov 1, 2012 at 10:14 PM, Dmitry Vyukov <dvyu...@google.com> wrote: >>> >>> >> > On Wed, Oct 31, 2012 at 11:00:17PM -0700, Xinliang David Li wrote: >>> >> >> > + /* Below are things we do not instrument >>> >> >> > + (no possibility of races or not implemented yet). */ >>> >> >> > + if (/* Compiler-emitted artificial variables. */ >>> >> >> > + (DECL_P (expr) && DECL_ARTIFICIAL (expr)) >>> >> >> > + /* The var does not live in memory -> no possibility of >>> >> >> > races. >>> >> >> > */ >>> >> >> > + || (tcode == VAR_DECL >>> >> >> > + && TREE_ADDRESSABLE (expr) == 0 >>> >> >> >>> >> >> ==> !TREE_ADDRESSABLE (expr) >>> >> >> >>> >> >> > + && TREE_STATIC (expr) == 0) >>> >> >> >>> >> >> >>> >> >> To detect stack varaible, TREE_STATIC can not be used. Use >>> >> >> !DECL_EXTERNAL instead. >>> >> > >>> >> > TREE_STATIC is right for that. >>> >> >>> >> Hmm, what does this condition try to capture then? >>> > >>> > >>> > >>> > As far as I remember, I've seen global variables marked as >>> > !ADDRESSABLE. And >>> > this condition is to instrument global vars in any case. >>> > But it was a long time ago. >>> >>> But it skips those globals without static storage and marked as not >>> addressable. >>> >>> It seems to me you want to skip all stack local variables that are not >>> address escaped. >> >> >> Yes, that's correct. I am pretty sure I implemented it incorrectly :) > > > > The high-level intention is to skip memory accesses that can't constitute a > data race. > Originally there were some other checks, e.g. check for loads from vtable. >
That should be caught by the is_load_const check there. David > > >> >> >>> >>> Without address escape analysis, the address taken >>> bit (not the same as addressable attribute) should be used. As far as >>> I can tell, such bit is not available in var_decl. The varpool_node >>> has one, but it is only for var_decls with static storage. It is also >>> unfortunate that there is no single bit to test if a variable is >>> function auto, though there is an interface to call which is >>> 'auto_var_in_fn_p (...)'. The condition to skip such variable >>> references are: >>> >>> if (tcode == VAR_DECL && auto_var_in_fn_p (expr, ..) && >>> !address_taken (expr)) >>> >>> The TREE_ADDRESSABLE check seems redundant -- if the var_decl (instead >>> of ssa name) appears in the assignment, why would it not be >>> 'addressable'? And being addressable does not mean it is address taken >>> either. >>> >>> Diego, is there a way to check address taken attribute for auto vars? >>> >>> thanks, >>> >>> David >> >> >
