[PATCH] Fix fallout of CFG scanning patch

[Eric Botcazou]

Hi,

This is another fallout of Zdenek's CFG scanning patch, this time for the Ada 
compiler on the attached testcase:

eric@linux:~/build/gcc/native32> gcc/xgcc -Bgcc -S -O p.adb -I gcc/ada/rts
p.adb:11:07: warning: variable "Tmp_Res" is read but never assigned
+===========================GNAT BUG DETECTED==============================+
| 4.3.0 20070501 (experimental) (i586-suse-linux-gnu) GCC error:           |
| in iterate_fix_dominators, at dominance.c:1044                           |
| Error detected at p.adb:26:1                        

The ICE occurs at the end of the DOM pass, when EH edges are purged:

  /* Removal of statements may make some EH edges dead.  Purge
     such edges from the CFG as needed.  */
  if (!bitmap_empty_p (need_eh_cleanup))
    {
      cfg_altered |= tree_purge_all_dead_eh_edges (need_eh_cleanup);
      bitmap_zero (need_eh_cleanup);
    }

  if (cfg_altered)
    free_dominance_info (CDI_DOMINATORS);


The pass has already modified the CFG (threaded a jump) so my understanding is 
that the dominance info are outdated.  Before Zdenek's patch, purging EH edges
would automatically invalidate the info; after Zdenek's patch, the compiler 
will try to incrementally (and locally) update them.  The problem is that it 
now starts from wrong info so it cannot compute a consistent result.

Hence the proposed patch, which moves up the calls to free_dominance_info.
It also occured to me that cfg_altered is never reset throughout the code!

Bootstrapped/regtested on i586-suse-linux, OK for mainline?


2007-05-06  Eric Botcazou  <ebotcazou@adacore.com>

	* tree-ssa-dom.c (tree_ssa_dominator_optimize): Reset cfg_altered.
	Free dominance info before purging EH edges as well as after.
	(eliminate_degenerate_phis): Likewise.
	(propagate_rhs_into_lhs): Set cfg_altered to true instead of 1.
	
	
2007-05-06  Eric Botcazou  <ebotcazou@adacore.com>

	* gnat.dg/opt1.ad[sb]: New testcase.


-- 
Eric Botcazou
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