re PR tree-optimization/34244 (VRP/SCEV miscompiles Firefox)

	PR tree-optimization/34244
	* tree-vrp.c (adjust_range_with_scev): Clear scev cache.
	(record_numbers_of_iterations): New function.
	(execute_vrp): Cache the numbers of iterations of loops.
	* tree-scalar-evolution.c (scev_reset_except_niters):
	New function.
	(scev_reset): Use scev_reset_except_niters.
	* tree-scalar-evolution.h (scev_reset_except_niters): Declare.

	* gcc.dg/tree-ssa/pr34244.c: New test.

From-SVN: r130527

1 files changed, 32 insertions, 0 deletions

diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index 00264d9..1e1ffaa 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -2636,6 +2636,13 @@ adjust_range_with_scev (value_range_t *vr, struct loop *loop, tree stmt,
   if (vr->type == VR_ANTI_RANGE)
     return;
 
+  /* Ensure that there are not values in the scev cache based on assumptions
+     on ranges of ssa names that were changed
+     (in set_value_range/set_value_range_to_varying).  Preserve cached numbers
+     of iterations, that were computed before the start of VRP (we do not
+     recompute these each time to save the compile time).  */
+  scev_reset_except_niters ();
+
   chrec = instantiate_parameters (loop, analyze_scalar_evolution (loop, var));
 
   /* Like in PR19590, scev can return a constant function.  */
@@ -6047,6 +6054,20 @@ vrp_finalize (void)
   vr_phi_edge_counts = NULL;
 }
 
+/* Calculates number of iterations for all loops, to ensure that they are
+   cached.  */
+
+static void
+record_numbers_of_iterations (void)
+{
+  loop_iterator li;
+  struct loop *loop;
+
+  FOR_EACH_LOOP (li, loop, 0)
+    {
+      number_of_latch_executions (loop);
+    }
+}
 
 /* Main entry point to VRP (Value Range Propagation).  This pass is
    loosely based on J. R. C. Patterson, ``Accurate Static Branch
@@ -6101,6 +6122,17 @@ execute_vrp (void)
 
   insert_range_assertions ();
 
+  /* Compute the # of iterations for each loop before we start the VRP
+     analysis.  The value ranges determined by VRP are used in expression
+     simplification, that is also used by the # of iterations analysis.
+     However, in the middle of the VRP analysis, the value ranges do not take
+     all the possible paths in CFG into account, so they do not have to be
+     correct, and the # of iterations analysis can obtain wrong results.
+     This is a problem, since the results of the # of iterations analysis
+     are cached, so these mistakes would not be corrected when the value
+     ranges are corrected.  */
+  record_numbers_of_iterations ();
+
   vrp_initialize ();
   ssa_propagate (vrp_visit_stmt, vrp_visit_phi_node);
   vrp_finalize ();