[patch] Fix for PR17520

[patch] Fix for PR17520

[Sebastian Pop]

Here is the patch that solves the compile time regression for PR17520.
The solution is to give up as soon as we detect that the result is
chrec_dont_know instead of iterating over all the edges.

Bootstrapped and tested on i686-pc-linux-gnu.

2004-10-11  Sebastian Pop  <pop@cri.ensmp.fr>

	* tree-scalar-evolution.c (follow_ssa_edge_in_condition_phi): 
	Give up as soon as the evolution is known not computable.

Index: tree-scalar-evolution.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-scalar-evolution.c,v
retrieving revision 2.8
diff -d -u -p -r2.8 tree-scalar-evolution.c
--- tree-scalar-evolution.c	1 Oct 2004 09:05:57 -0000	2.8
+++ tree-scalar-evolution.c	11 Oct 2004 11:07:57 -0000
@@ -1398,6 +1398,11 @@ follow_ssa_edge_in_condition_phi (struct
 
   for (i = 1; i < PHI_NUM_ARGS (condition_phi); i++)
     {
+      /* Quickly give up when the evolution of one of the branches is
+	 not known.  */
+      if (*evolution_of_loop == chrec_dont_know)
+	return true;
+
       if (!follow_ssa_edge_in_condition_phi_branch (i, loop, condition_phi,
 						    halting_phi,
 						    &evolution_of_branch,