Re: [tree-ssa]: PRE updates

[Daniel Berlin <dberlin at dberlin dot org>]

On Wednesday, June 11, 2003, at 03:49  PM, Andrew MacLeod wrote:

> On Tue, 2003-06-10 at 19:08, Daniel Berlin wrote:
> > Updates for PRE make it do the right thing in more cases, and faster.
> > Also added a bit more dump info.
> > Eventually, we should be able to get the temporary without ever 
> > needing to
> > call get_reaching_def.
> > It'll mean i have to look more at open64's injury/repair stuff for
> > strength reduction, in order to get the temporary right for those 
> > cases.
> >
> > I now get stopped in the bootstrap here:
> > c-parse.c: In function `yyparse':
> > c-parse.c:5421: internal compiler error: in coalesce_ssa_name, at
> > tree-ssa.c:1350
> > Please submit a full bug report,
> > with preprocessed source if appropriate.
> > See <URL:http://gcc.gnu.org/bugs.html> for instructions.
> >
> >
> > Andrew, this is *with* your phi updating patch. Without it, we get 
> > the phi
> > node abort we discussed before the weekend. I'll note that this
> > file/function is the first file that requires splitting an edge to do 
> > an
> > insertion where it has  to update the phi's, and the location of the 
> > abort
> > gives me the feeling something else needs to be updated (maybe 
> > dominator
> > children or something? I haven't looked).
>
> SO when you split an edge, the current routines will take care of
> adjusting existing PHI's. What they dont do is take care of any new
> PHI's you are adding.
>
> The failure here is because  you inserted a stmt on the edge from the 
> IF
> to the next stmt. There was no else caluse, so the insert routines
> placed your stmt in the else clause of the IF stmt:
>
>           else
>             {
>
>               # BLOCK 1730.  PRED: 748.  SUCC: 754.
>               pretmp.1473_8344 = yyvsp_27 + -4B           <<-- 
> Inserted stmt
>             };
>
>           # BLOCK 754 (pre.i:18276).  PRED: 1730 753 749.  SUCC: 1681.
>           #   pretmp.1473_8320 = PHI <pretmp.1473_8344(748), 
> pretmp.1473_8360(749), pretmp.1473_8360(753)>;
>
>
> But the PHI you created still uses the original basic block of the IF
> (Ie, the PRED of the else block.).
My fault, i forgot to update the euse to the newly created block, (and 
update the EPHI edge) so it thinks it's on the old edge (where it would 
have been had the block not been split).

> So the PHI node says it gets pretmp.1473_8344 from BB 748, and the live
> reange routines find no def on that path, so they make it live on 
> entry.
> The same situation existed for pretmp.1473_8343, so it was marked as
> live on entry.  Since they were both live on entry, both need to
> coalesce to the same memory location, but they also interfere over the
> range they are live, so its an impossible situation, and hence the
> abort.

> So, are you inserting a stmt at a time, or inserting them all and then
> commiting?

Inserting one at a time and committing at the same time.

> If edges are split, and a new basic block is going to be created, you
> are going to need to know that to create your PHI node properly.
>
>
> Andrew