------- Comment #5 from rguenther at suse dot de 2009-04-01 14:10 -------
Subject: Re: [4.3/4.4/4.5 Regression] tree-ssa-sink
breaks stack layout
On Wed, 1 Apr 2009, jakub at gcc dot gnu dot org wrote:
> ------- Comment #3 from jakub at gcc dot gnu dot org 2009-04-01 14:00 -------
> Even for live range analysis of the vars that must go into stack the block
> info
> needs to be used, otherwise once address of a stack var escapes, you'd have to
> assume it is live almost till the end of the function (at least live on any
> function calls that might see it through global state, or global ptr
> dereferences etc.). Using the block info, you can find out that:
> {
> char buf[10];
> foo (buf);
> bar ();
> }
> baz ();
> in baz () call the buf var doesn't need to be live anymore. At least short
> term I think it would be best just to walk the function to be expanded, look
> at
> all gimple_block BLOCKs referenced and note which originally non-overlapping
> BLOCKs are indeed still non-overlapping after the tree passes and don't
> consider originally non-overlapping BLOCKs during stack slot sharing decisions
> if they are overlapping.
Note that once we use more precise alias information during RTL
optimizations (via alias exports patch) avoiding stack slot sharing
solely based on type-based conflicts will no longer be working.
Richard.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39604
