[PATCH][1/2] Fix PR77768

[Richard Biener]

On Thu, 29 Sep 2016, Markus Trippelsdorf wrote:

> On 2016.09.28 at 13:33 +0200, Richard Biener wrote:
> > 
> > I am testing the following patch to avoid useless VRP range allocations
> > when we just ask for varying on stmts we don't know how to handle.
> > I think it should fix the PR where we end up assigning to the
> > static const vr_const_varying returned by get_value_range in the early VRP
> > context.
> > 
> > Eventually the VRP lattice needs to become sparse (or just growable, I 
> > have a patch for that as well).  Not until early VRP gets some more
> > capabilities though, it would be a waste otherwise.
> > 
> > Bootstrap / regtest in progress on x86_64-unknown-linux-gnu.
> 
> You probably noticed this yourself, but the patch causes conftests to
> spin during stageprofile. For example libiberty:
> 
> configure:6516: checking for working fork
> configure:6538:  /home/trippels/gcc_build_dir_/./prev-gcc/xgcc -B/home/trippels/gcc_build_dir_/./prev-gcc/ -B/usr/local/powerpc64le-unknown-linux-gnu/bin/ -B/usr/local/powerpc64le-unknown-linux-gnu/bin/ -B/usr/local/powerpc64le-unknown-linux-gnu/lib/ -isystem /usr/local/powerpc64le-unknown-linux-gnu/include -isystem /usr/local/powerpc64le-unknown-linux-gnu/sys-include    -o conftest -mcpu=power8 -O3 -pipe -gtoggle -fprofile-generate  -static-libstdc++ -static-libgcc  conftest.c  >&5
> configure:6538: $? = 0
> configure:6538: ./conftest
> <<spinning>>

I did.  The following is what I have installed (not allocating the
ranges doesn't work - they end up UNDEFINED, but we can avoid storing
to already VR_VARYING ones).

Bootstrapped / tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2016-09-29  Richard Biener  <rguenther@suse.de>

	* tree-vrp.c (set_defs_to_varying): New helper avoiding
	writing to vr_const_varying.
	(vrp_initialize): Call it.
	(vrp_visit_stmt): Likewise.
	(evrp_dom_walker::before_dom_children): Likewise.

Index: gcc/tree-vrp.c
===================================================================
--- gcc/tree-vrp.c	(revision 240568)
+++ gcc/tree-vrp.c	(working copy)
@@ -710,6 +710,23 @@ get_value_range (const_tree var)
   return vr;
 }
 
+/* Set value-ranges of all SSA names defined by STMT to varying.  */
+
+static void
+set_defs_to_varying (gimple *stmt)
+{
+  ssa_op_iter i;
+  tree def;
+  FOR_EACH_SSA_TREE_OPERAND (def, stmt, i, SSA_OP_DEF)
+    {
+      value_range *vr = get_value_range (def);
+      /* Avoid writing to vr_const_varying get_value_range may return.  */
+      if (vr->type != VR_VARYING)
+	set_value_range_to_varying (vr);
+    }
+}
+
+
 /* Return true, if VAL1 and VAL2 are equal values for VRP purposes.  */
 
 static inline bool
@@ -7022,10 +7039,7 @@ vrp_initialize ()
 	    prop_set_simulate_again (stmt, true);
 	  else if (!stmt_interesting_for_vrp (stmt))
 	    {
-	      ssa_op_iter i;
-	      tree def;
-	      FOR_EACH_SSA_TREE_OPERAND (def, stmt, i, SSA_OP_DEF)
-		set_value_range_to_varying (get_value_range (def));
+	      set_defs_to_varying (stmt);
 	      prop_set_simulate_again (stmt, false);
 	    }
 	  else
@@ -7901,8 +7915,6 @@ vrp_visit_stmt (gimple *stmt, edge *take
 {
   value_range vr = VR_INITIALIZER;
   tree lhs = gimple_get_lhs (stmt);
-  tree def;
-  ssa_op_iter iter;
   extract_range_from_stmt (stmt, taken_edge_p, output_p, &vr);
 
   if (*output_p)
@@ -7997,8 +8009,7 @@ vrp_visit_stmt (gimple *stmt, edge *take
 
   /* All other statements produce nothing of interest for VRP, so mark
      their outputs varying and prevent further simulation.  */
-  FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)
-    set_value_range_to_varying (get_value_range (def));
+  set_defs_to_varying (stmt);
 
   return (*taken_edge_p) ? SSA_PROP_INTERESTING : SSA_PROP_VARYING;
 }
@@ -10726,12 +10737,7 @@ evrp_dom_walker::before_dom_children (ba
 	      && (vr.type == VR_RANGE || vr.type == VR_ANTI_RANGE))
 	    update_value_range (output, &vr);
 	  else
-	    {
-	      tree def;
-	      ssa_op_iter iter;
-	      FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)
-		set_value_range_to_varying (get_value_range (def));
-	    }
+	    set_defs_to_varying (stmt);
 
 	  /* Try folding stmts with the VR discovered.  */
 	  bool did_replace
@@ -10780,12 +10786,7 @@ evrp_dom_walker::before_dom_children (ba
 	    }
 	}
       else
-	{
-	  tree def;
-	  ssa_op_iter iter;
-	  FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)
-	    set_value_range_to_varying (get_value_range (def));
-	}
+	set_defs_to_varying (stmt);
     }
   bb->flags |= BB_VISITED;
   return NULL;