Re: [RFC][IPA-VRP] Early VRP Implementation

[kugan <kugan dot vivekanandarajah at linaro dot org>]

Hi Richard,

On 12/08/16 20:43, Richard Biener wrote:
> On Wed, Aug 3, 2016 at 3:17 AM, kugan <kugan.vivekanandarajah@linaro.org> wrote:

[SNIP]

> diff --git a/gcc/common.opt b/gcc/common.opt
> index 8a292ed..7028cd4 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -2482,6 +2482,10 @@ ftree-vrp
>  Common Report Var(flag_tree_vrp) Init(0) Optimization
>  Perform Value Range Propagation on trees.
>
> +fdisable-tree-evrp
> +Common Report Var(flag_disable_early_vrp) Init(0) Optimization
> +Disable Early Value Range Propagation on trees.
> +
>
> no please, this is automatically supported via -fdisable-

I am now having -ftree-evrp which is enabled all the time. But This will 
only be used for disabling the early-vrp. That is, early-vrp will be run 
when ftree-vrp is enabled and ftree-evrp is not explicitly disabled. Is 
this OK?

> @@ -1728,11 +1736,12 @@ extract_range_from_assert (value_range *vr_p, tree expr)
>      always false.  */
>
>  static void
> -extract_range_from_ssa_name (value_range *vr, tree var)
> +extract_range_from_ssa_name (value_range *vr, bool dom_p, tree var)
>  {
>    value_range *var_vr = get_value_range (var);
>
> -  if (var_vr->type != VR_VARYING)
> +  if (var_vr->type != VR_VARYING
> +      && (!dom_p || var_vr->type != VR_UNDEFINED))
>      copy_value_range (vr, var_vr);
>    else
>      set_value_range (vr, VR_RANGE, var, var, NULL);
>
> why do you need these changes?  I think I already told you you need to
> initialize the lattice to sth else than VR_UNDEFINED and that you can't
> fully re-use update_value_range.  If you don't want to do that then instead
> of doing changes all over the place do it in get_value_range and have a
> global flag.

I have now added a global early_vrp_p and use this to initialize 
VR_INITIALIZER and get_value_range default to VR_VARYING.

> @@ -3594,7 +3643,8 @@ extract_range_from_cond_expr (value_range *vr,
> gassign *stmt)
>     on the range of its operand and the expression code.  */
>
>  static void
> -extract_range_from_comparison (value_range *vr, enum tree_code code,
> +extract_range_from_comparison (value_range *vr,
> +                              enum tree_code code,
>                                tree type, tree op0, tree op1)
>  {
>    bool sop = false;
>
> remove these kind of no-op changes.

Done.

> +/* Initialize local data structures for VRP.  If DOM_P is true,
> +   we will be calling this from early_vrp where value range propagation
> +   is done by visiting stmts in dominator tree.  ssa_propagate engine
> +   is not used in this case and that part of the ininitialization will
> +   be skipped.  */
>
>  static void
> -vrp_initialize (void)
> +vrp_initialize (bool dom_p)
>  {
>    basic_block bb;
>
> @@ -6949,6 +7010,9 @@ vrp_initialize (void)
>    vr_phi_edge_counts = XCNEWVEC (int, num_ssa_names);
>    bitmap_obstack_initialize (&vrp_equiv_obstack);
>
> +  if (dom_p)
> +    return;
> +
>
> split the function instead.
>
> @@ -7926,7 +7992,8 @@ vrp_visit_switch_stmt (gswitch *stmt, edge *taken_edge_p)
>     If STMT produces a varying value, return SSA_PROP_VARYING.  */
>
>  static enum ssa_prop_result
> -vrp_visit_stmt (gimple *stmt, edge *taken_edge_p, tree *output_p)
> +vrp_visit_stmt_worker (gimple *stmt, bool dom_p,  edge *taken_edge_p,
> +                      tree *output_p)
>  {
>    tree def;
>    ssa_op_iter iter;
> @@ -7940,7 +8007,7 @@ vrp_visit_stmt (gimple *stmt, edge
> *taken_edge_p, tree *output_p)
>    if (!stmt_interesting_for_vrp (stmt))
>      gcc_assert (stmt_ends_bb_p (stmt));
>    else if (is_gimple_assign (stmt) || is_gimple_call (stmt))
> -    return vrp_visit_assignment_or_call (stmt, output_p);
> +    return vrp_visit_assignment_or_call (stmt, dom_p, output_p);
>    else if (gimple_code (stmt) == GIMPLE_COND)
>      return vrp_visit_cond_stmt (as_a <gcond *> (stmt), taken_edge_p);
>    else if (gimple_code (stmt) == GIMPLE_SWITCH)
> @@ -7954,6 +8021,12 @@ vrp_visit_stmt (gimple *stmt, edge
> *taken_edge_p, tree *output_p)
>    return SSA_PROP_VARYING;
>  }
>
> +static enum ssa_prop_result
> +vrp_visit_stmt (gimple *stmt, edge *taken_edge_p, tree *output_p)
> +{
> +  return vrp_visit_stmt_worker (stmt, false, taken_edge_p, output_p);
> +}
>
> as said the refactoring that would be appreciated is to split out the
> update_value_range calls
> from the worker functions so you can call the respective functions
> from the DOM implementations.
> That they are globbed in vrp_visit_stmt currently is due to the API of
> the SSA propagator.
Sent this as separate patch for easy reviewing and testing.

> @@ -8768,6 +8842,12 @@ vrp_visit_phi_node (gphi *phi)
>               fprintf (dump_file, "\n");
>             }
>
> +         if (dom_p && vr_arg.type == VR_UNDEFINED)
> +           {
> +             set_value_range_to_varying (&vr_result);
> +             break;
> +           }
> +
>
> eh...  ok, so another way to attack this is, instead of initializing
> the lattice to sth else
> than VR_UNDEFINED, make sure to drop the lattice to varying for all PHI args on
> yet unvisited incoming edges (you're not doing optimistic VRP).  That's the only
> place you _have_ to do it.

Even when it is initialize (as I am doing now), we can still end up with 
VR_UNDEFINED during the propagation.  I have just left the above so that 
we dont end up with the wrong VR.

I also noticed that g++.dg/warn/pr33738.C testcase is now failing. This 
is because, with early-vrp setting value range ccp2 is optimizing 
without issuing a warning. I will look into it.

bootstrap and regression testing is in progress.

Thanks,
Kugan

>From 255054400db3f6cd20abc89f3735c7e488985c1e Mon Sep 17 00:00:00 2001
From: Kugan Vivekanandarajah <kugan.vivekanandarajah@linaro.org>
Date: Mon, 15 Aug 2016 10:11:36 +1000
Subject: [PATCH 3/5] Add Early VRP

---
 gcc/common.opt                            |   4 +
 gcc/doc/invoke.texi                       |   9 +
 gcc/passes.def                            |   1 +
 gcc/testsuite/g++.dg/tree-ssa/pr31146-2.C |   2 +-
 gcc/testsuite/gcc.dg/tree-ssa/evrp1.c     |  13 +
 gcc/testsuite/gcc.dg/tree-ssa/evrp2.c     |  18 ++
 gcc/testsuite/gcc.dg/tree-ssa/evrp3.c     |  15 ++
 gcc/testsuite/gcc.dg/tree-ssa/pr22117.c   |   2 +-
 gcc/testsuite/gcc.dg/tree-ssa/pr25382.c   |   2 +-
 gcc/testsuite/gcc.dg/tree-ssa/vrp58.c     |   4 +-
 gcc/testsuite/gcc.dg/tree-ssa/vrp67.c     |   5 +-
 gcc/timevar.def                           |   1 +
 gcc/tree-pass.h                           |   1 +
 gcc/tree-vrp.c                            | 419 ++++++++++++++++++++++++++----
 14 files changed, 434 insertions(+), 62 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/evrp1.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/evrp2.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/evrp3.c

diff --git a/gcc/common.opt b/gcc/common.opt
index 65a9762..aec618e 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2499,6 +2499,10 @@ ftree-vrp
 Common Report Var(flag_tree_vrp) Init(0) Optimization
 Perform Value Range Propagation on trees.
 
+ftree-evrp
+Common Report Var(flag_early_vrp) Init(1) Optimization
+This can be used to disable Early Value Range Propagation on trees.
+
 fsplit-paths
 Common Report Var(flag_split_paths) Init(0) Optimization
 Split paths leading to loop backedges.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index d04be6f..3cad409 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -7715,6 +7715,10 @@ enabled by default at @option{-O2} and higher.  Null pointer check
 elimination is only done if @option{-fdelete-null-pointer-checks} is
 enabled.
 
+@item -fdisable-tree-evrp
+@opindex fdisable-tree-evrp
+Disables Early Value Range Propagation on trees.
+
 @item -fsplit-paths
 @opindex fsplit-paths
 Split paths leading to loop backedges.  This can improve dead code
@@ -12350,6 +12354,11 @@ is made by appending @file{.slp} to the source file name.
 Dump each function after Value Range Propagation (VRP).  The file name
 is made by appending @file{.vrp} to the source file name.
 
+@item early vrp
+@opindex fdump-tree-evrp
+Dump each function after Early Value Range Propagation (EVRP).  The file name
+is made by appending @file{.evrp} to the source file name.
+
 @item oaccdevlow
 @opindex fdump-tree-oaccdevlow
 Dump each function after applying device-specific OpenACC transformations.
diff --git a/gcc/passes.def b/gcc/passes.def
index 3647e90..ebd360b 100644
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -89,6 +89,7 @@ along with GCC; see the file COPYING3.  If not see
 	     execute TODO_rebuild_alias at this point.  */
 	  NEXT_PASS (pass_build_ealias);
 	  NEXT_PASS (pass_fre);
+	  NEXT_PASS (pass_early_vrp);
 	  NEXT_PASS (pass_merge_phi);
           NEXT_PASS (pass_dse);
 	  NEXT_PASS (pass_cd_dce);
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr31146-2.C b/gcc/testsuite/g++.dg/tree-ssa/pr31146-2.C
index 5e09583..dce05d6 100644
--- a/gcc/testsuite/g++.dg/tree-ssa/pr31146-2.C
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr31146-2.C
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-forwprop1" } */
+/* { dg-options "-O -fno-tree-evrp -fdump-tree-forwprop1" } */
 
 #include <new>
 
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/evrp1.c b/gcc/testsuite/gcc.dg/tree-ssa/evrp1.c
new file mode 100644
index 0000000..8c6e4e6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/evrp1.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-evrp" } */
+
+int foo (int i);
+int bar (int j)
+{
+  if (j > 2)
+    return foo (j + 2);
+  else
+    return j;
+}
+
+/* { dg-final { scan-tree-dump "\\\[5, \\+INF" "evrp" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/evrp2.c b/gcc/testsuite/gcc.dg/tree-ssa/evrp2.c
new file mode 100644
index 0000000..e6d4235
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/evrp2.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-evrp" } */
+
+int foo (int i);
+int bar2 (int j)
+{
+  if (j > 2)
+    {
+      if (j < 7)
+	return foo (j + 1);
+      else
+	return foo (j + 2);
+    }
+  return j;
+}
+
+
+/* { dg-final { scan-tree-dump "\\\[4, 7\\\]" "evrp" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/evrp3.c b/gcc/testsuite/gcc.dg/tree-ssa/evrp3.c
new file mode 100644
index 0000000..1a3bbd5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/evrp3.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-evrp" } */
+
+int foo (int i);
+void bar (int j)
+{
+  unsigned int i;
+  for (i = 0; i < 10; ++i)
+    {
+      bar (i + 1);
+    }
+}
+
+/* { dg-final { scan-tree-dump "\\\[1, 10\\\]" "evrp" } } */
+
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr22117.c b/gcc/testsuite/gcc.dg/tree-ssa/pr22117.c
index 7efdd63..d4fcdfe 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr22117.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr22117.c
@@ -3,7 +3,7 @@
    known to be zero after entering the first two "if" statements.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1" } */
+/* { dg-options "-O2 -fno-tree-evrp -fdump-tree-vrp1" } */
 
 void link_error (void);
 
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr25382.c b/gcc/testsuite/gcc.dg/tree-ssa/pr25382.c
index dcf9148..c4fda8b 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr25382.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr25382.c
@@ -3,7 +3,7 @@
    Check that VRP now gets ranges from BIT_AND_EXPRs.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O2 -fno-tree-ccp -fdump-tree-vrp1" } */
+/* { dg-options "-O2 -fno-tree-ccp -fdump-tree-vrp" } */
 
 int
 foo (int a)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp58.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp58.c
index 5b44ae2..6df91ca 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/vrp58.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp58.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1-details" } */
+/* { dg-options "-O2 -fdump-tree-evrp-details" } */
 
 long long
 foo (long long a, signed char b, signed char c)
@@ -9,4 +9,4 @@ foo (long long a, signed char b, signed char c)
 }
 
 /* { dg-final { scan-tree-dump "Folded into" "vrp1" { target int32plus } } } */
-/* { dg-final { scan-tree-dump "Folding statement: _\[0-9\]\* = \\(long long int\\) bc_\[0-9\]\*;" "vrp1" { target int16 } } } */
+/* { dg-final { scan-tree-dump "Folding statement: _\[0-9\]\* = \\(long long int\\) bc_\[0-9\]\*;" "evrp" { target int16 } } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp67.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp67.c
index ef5e8f9..ec1cc9a 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/vrp67.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp67.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1" } */
+/* { dg-options "-O2 -fdump-tree-ccp2 -fdump-tree-vrp1" } */
 
 extern void link_error (void);
 
@@ -36,4 +36,5 @@ unsigned baz (unsigned i)
   return i;
 }
 
-/* { dg-final { scan-tree-dump-times "Folding predicate" 3 "vrp1" } } */
+/* { dg-final { scan-tree-dump-times "Folding predicate" 1 "ccp2" } } */
+/* { dg-final { scan-tree-dump-times "Folding predicate" 2 "vrp1" } } */
diff --git a/gcc/timevar.def b/gcc/timevar.def
index 5f12118..8837832 100644
--- a/gcc/timevar.def
+++ b/gcc/timevar.def
@@ -149,6 +149,7 @@ DEFTIMEVAR (TV_TREE_CFG		     , "tree CFG construction")
 DEFTIMEVAR (TV_TREE_CLEANUP_CFG	     , "tree CFG cleanup")
 DEFTIMEVAR (TV_TREE_TAIL_MERGE       , "tree tail merge")
 DEFTIMEVAR (TV_TREE_VRP              , "tree VRP")
+DEFTIMEVAR (TV_TREE_EARLY_VRP        , "tree Early VRP")
 DEFTIMEVAR (TV_TREE_COPY_PROP        , "tree copy propagation")
 DEFTIMEVAR (TV_FIND_REFERENCED_VARS  , "tree find ref. vars")
 DEFTIMEVAR (TV_TREE_PTA		     , "tree PTA")
diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
index 36299a6..d836d57 100644
--- a/gcc/tree-pass.h
+++ b/gcc/tree-pass.h
@@ -440,6 +440,7 @@ extern gimple_opt_pass *make_pass_fre (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_check_data_deps (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_copy_prop (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_isolate_erroneous_paths (gcc::context *ctxt);
+extern gimple_opt_pass *make_pass_early_vrp (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_vrp (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_uncprop (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_return_slot (gcc::context *ctxt);
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index b56ceec..1eb0fa7 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -62,7 +62,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "alloc-pool.h"
 #include "domwalk.h"
 
-#define VR_INITIALIZER { VR_UNDEFINED, NULL_TREE, NULL_TREE, NULL }
+#define VR_INITIALIZER { early_vrp_p ? VR_VARYING: VR_UNDEFINED, NULL_TREE, NULL_TREE, NULL }
 
 /* Allocation pools for tree-vrp allocations.  */
 static object_allocator<value_range> vrp_value_range_pool ("Tree VRP value ranges");
@@ -72,6 +72,9 @@ static bitmap_obstack vrp_equiv_obstack;
    for still active basic-blocks.  */
 static sbitmap *live;
 
+/* True if we are in DOM based Early VRP.  */
+static bool early_vrp_p = false;
+
 /* Return true if the SSA name NAME is live on the edge E.  */
 
 static bool
@@ -669,6 +672,8 @@ get_value_range (const_tree var)
   /* Create a default value range.  */
   vr_value[ver] = vr = vrp_value_range_pool.allocate ();
   memset (vr, 0, sizeof (*vr));
+  if (early_vrp_p)
+    vr->type = VR_VARYING;
 
   /* Defer allocating the equivalence set.  */
   vr->equiv = NULL;
@@ -1441,44 +1446,17 @@ op_with_boolean_value_range_p (tree op)
 	  && integer_onep (vr->max));
 }
 
-/* Extract value range information from an ASSERT_EXPR EXPR and store
-   it in *VR_P.  */
+/* Extract value range information for VAR when (OP COND_CODE LIMIT) is
+   true and store it in *VR_P.  */
 
 static void
-extract_range_from_assert (value_range *vr_p, tree expr)
+extract_range_for_var_from_comparison_expr (tree var, enum tree_code cond_code,
+					    tree op, tree limit,
+					    value_range *vr_p)
 {
-  tree var, cond, limit, min, max, type;
+  tree  min, max, type;
   value_range *limit_vr;
-  enum tree_code cond_code;
-
-  var = ASSERT_EXPR_VAR (expr);
-  cond = ASSERT_EXPR_COND (expr);
-
-  gcc_assert (COMPARISON_CLASS_P (cond));
-
-  /* Find VAR in the ASSERT_EXPR conditional.  */
-  if (var == TREE_OPERAND (cond, 0)
-      || TREE_CODE (TREE_OPERAND (cond, 0)) == PLUS_EXPR
-      || TREE_CODE (TREE_OPERAND (cond, 0)) == NOP_EXPR)
-    {
-      /* If the predicate is of the form VAR COMP LIMIT, then we just
-	 take LIMIT from the RHS and use the same comparison code.  */
-      cond_code = TREE_CODE (cond);
-      limit = TREE_OPERAND (cond, 1);
-      cond = TREE_OPERAND (cond, 0);
-    }
-  else
-    {
-      /* If the predicate is of the form LIMIT COMP VAR, then we need
-	 to flip around the comparison code to create the proper range
-	 for VAR.  */
-      cond_code = swap_tree_comparison (TREE_CODE (cond));
-      limit = TREE_OPERAND (cond, 0);
-      cond = TREE_OPERAND (cond, 1);
-    }
-
   limit = avoid_overflow_infinity (limit);
-
   type = TREE_TYPE (var);
   gcc_assert (limit != var);
 
@@ -1524,15 +1502,15 @@ extract_range_from_assert (value_range *vr_p, tree expr)
      as well build the range [b_4, +INF] for it.
      One special case we handle is extracting a range from a
      range test encoded as (unsigned)var + CST <= limit.  */
-  if (TREE_CODE (cond) == NOP_EXPR
-      || TREE_CODE (cond) == PLUS_EXPR)
+  if (TREE_CODE (op) == NOP_EXPR
+      || TREE_CODE (op) == PLUS_EXPR)
     {
-      if (TREE_CODE (cond) == PLUS_EXPR)
+      if (TREE_CODE (op) == PLUS_EXPR)
         {
-          min = fold_build1 (NEGATE_EXPR, TREE_TYPE (TREE_OPERAND (cond, 1)),
-			     TREE_OPERAND (cond, 1));
+	  min = fold_build1 (NEGATE_EXPR, TREE_TYPE (TREE_OPERAND (op, 1)),
+			     TREE_OPERAND (op, 1));
           max = int_const_binop (PLUS_EXPR, limit, min);
-	  cond = TREE_OPERAND (cond, 0);
+	  op = TREE_OPERAND (op, 0);
 	}
       else
 	{
@@ -1716,6 +1694,41 @@ extract_range_from_assert (value_range *vr_p, tree expr)
   vrp_intersect_ranges (vr_p, get_value_range (var));
 }
 
+/* Extract value range information from an ASSERT_EXPR EXPR and store
+   it in *VR_P.  */
+
+static void
+extract_range_from_assert (value_range *vr_p, tree expr)
+{
+  tree var = ASSERT_EXPR_VAR (expr);
+  tree cond = ASSERT_EXPR_COND (expr);
+  tree limit, op;
+  enum tree_code cond_code;
+  gcc_assert (COMPARISON_CLASS_P (cond));
+
+  /* Find VAR in the ASSERT_EXPR conditional.  */
+  if (var == TREE_OPERAND (cond, 0)
+      || TREE_CODE (TREE_OPERAND (cond, 0)) == PLUS_EXPR
+      || TREE_CODE (TREE_OPERAND (cond, 0)) == NOP_EXPR)
+    {
+      /* If the predicate is of the form VAR COMP LIMIT, then we just
+	 take LIMIT from the RHS and use the same comparison code.  */
+      cond_code = TREE_CODE (cond);
+      limit = TREE_OPERAND (cond, 1);
+      op = TREE_OPERAND (cond, 0);
+    }
+  else
+    {
+      /* If the predicate is of the form LIMIT COMP VAR, then we need
+	 to flip around the comparison code to create the proper range
+	 for VAR.  */
+      cond_code = swap_tree_comparison (TREE_CODE (cond));
+      limit = TREE_OPERAND (cond, 0);
+      op = TREE_OPERAND (cond, 1);
+    }
+  extract_range_for_var_from_comparison_expr (var, cond_code, op,
+					      limit, vr_p);
+}
 
 /* Extract range information from SSA name VAR and store it in VR.  If
    VAR has an interesting range, use it.  Otherwise, create the
@@ -6938,19 +6951,28 @@ stmt_interesting_for_vrp (gimple *stmt)
   return false;
 }
 
-
-/* Initialize local data structures for VRP.  */
+/* Initialize VRP lattice.  */
 
 static void
-vrp_initialize (void)
+vrp_initialize_lattice ()
 {
-  basic_block bb;
-
   values_propagated = false;
   num_vr_values = num_ssa_names;
   vr_value = XCNEWVEC (value_range *, num_vr_values);
   vr_phi_edge_counts = XCNEWVEC (int, num_ssa_names);
   bitmap_obstack_initialize (&vrp_equiv_obstack);
+}
+
+/* Initialize local data structures for VRP.  If DOM_P is true,
+   we will be calling this from early_vrp where value range propagation
+   is done by visiting stmts in dominator tree.  ssa_propagate engine
+   is not used in this case and that part of the ininitialization will
+   be skipped.  */
+
+static void
+vrp_initialize ()
+{
+  basic_block bb;
 
   FOR_EACH_BB_FN (bb, cfun)
     {
@@ -8803,6 +8825,12 @@ vrp_visit_phi_node_worker (gphi *phi, value_range *vr_result)
 	      fprintf (dump_file, "\n");
 	    }
 
+	  if (early_vrp_p && vr_arg.type == VR_UNDEFINED)
+	    {
+	      set_value_range_to_varying (vr_result);
+	      break;
+	    }
+
 	  if (first)
 	    copy_value_range (vr_result, &vr_arg);
 	  else
@@ -8831,6 +8859,7 @@ vrp_visit_phi_node_worker (gphi *phi, value_range *vr_result)
      simulate this PHI again with the same number of edges then iterate
      one more time.  */
   if (edges > 0
+      && !early_vrp_p
       && gimple_phi_num_args (phi) > 1
       && edges == old_edges
       && lhs_vr->type != VR_UNDEFINED
@@ -8898,7 +8927,8 @@ scev_check:
      scev_check can be reached from two paths, one is a fall through from above
      "varying" label, the other is direct goto from code block which tries to
      avoid infinite simulation.  */
-  if ((l = loop_containing_stmt (phi))
+  if (!early_vrp_p
+      && (l = loop_containing_stmt (phi))
       && l->header == gimple_bb (phi))
     adjust_range_with_scev (vr_result, l, phi, lhs);
 
@@ -10419,6 +10449,22 @@ finalize_jump_threads (void)
   delete equiv_stack;
 }
 
+/* Free VRP lattice.  */
+
+static void
+vrp_free_lattice ()
+{
+  /* Free allocated memory.  */
+  free (vr_value);
+  free (vr_phi_edge_counts);
+  bitmap_obstack_release (&vrp_equiv_obstack);
+  vrp_value_range_pool.release ();
+
+  /* So that we can distinguish between VRP data being available
+     and not available.  */
+  vr_value = NULL;
+  vr_phi_edge_counts = NULL;
+}
 
 /* Traverse all the blocks folding conditionals with known ranges.  */
 
@@ -10465,17 +10511,237 @@ vrp_finalize (bool warn_array_bounds_p)
   /* We must identify jump threading opportunities before we release
      the datastructures built by VRP.  */
   identify_jump_threads ();
+}
 
-  /* Free allocated memory.  */
-  free (vr_value);
-  free (vr_phi_edge_counts);
-  bitmap_obstack_release (&vrp_equiv_obstack);
-  vrp_value_range_pool.release ();
+/* Check to see if the PHI stmt has any back edges.  In dominator based
+   VRP, if we have back-edges, we will have to set the resulting VR to
+   varying.  This is because we dont iteratetively visit the stmt till
+   we reach fixed point.  */
 
-  /* So that we can distinguish between VRP data being available
-     and not available.  */
-  vr_value = NULL;
-  vr_phi_edge_counts = NULL;
+static bool
+visit_phi_node_p (gphi *phi)
+{
+  for (unsigned int i = 0; i < gimple_phi_num_args (phi); i++)
+    {
+      edge e = gimple_phi_arg_edge (phi, i);
+      if (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
+	return false;
+    }
+  return true;
+}
+
+/* evrp_dom_walker visits the basic blocks in the dominance order and set
+   the Value Ranges (VR) for SSA_NAMEs in the scope.  Use this VR to
+   discover more VRs.  */
+
+class evrp_dom_walker : public dom_walker
+{
+public:
+  evrp_dom_walker ()
+    : dom_walker (CDI_DOMINATORS), stack (10) {}
+
+  virtual edge before_dom_children (basic_block);
+  virtual void after_dom_children (basic_block);
+  void push_value_range (const_tree var, value_range *vr);
+  value_range *pop_value_range (const_tree var);
+
+  /* Cond_stack holds the old VR.  */
+  auto_vec<std::pair <const_tree, value_range*> > stack;
+};
+
+/* See if there is any new scope is entered with new VR and set that VR to
+   ssa_name before visiting the statements in the scope.  */
+
+edge
+evrp_dom_walker::before_dom_children (basic_block bb)
+{
+  value_range *new_vr = NULL;
+  tree op0 = NULL_TREE;
+  push_value_range (NULL_TREE, NULL);
+  if (single_pred_p (bb))
+    {
+      edge e = single_pred_edge (bb);
+      value_range vr = VR_INITIALIZER;
+      gimple *stmt = last_stmt (e->src);
+      if (stmt
+	  && gimple_code (stmt) == GIMPLE_COND
+	  && (op0 = gimple_cond_lhs (stmt))
+	  && TREE_CODE (op0) == SSA_NAME
+	  && INTEGRAL_TYPE_P (TREE_TYPE (gimple_cond_lhs (stmt))))
+	{
+	  /* Entering a new scope.  Try to see if we can find a VR
+	     here.  */
+	  tree op1 = gimple_cond_rhs (stmt);
+	  tree_code code = gimple_cond_code (stmt);
+	  value_range *old_vr = get_value_range (op0);
+
+	  if (TREE_OVERFLOW_P (op1))
+	    op1 = drop_tree_overflow (op1);
+
+	  /* If condition is false, invert the cond.  */
+	  if (e->flags & EDGE_FALSE_VALUE)
+	    code = invert_tree_comparison (gimple_cond_code (stmt),
+					   HONOR_NANS (op0));
+	  /* Discover VR when condition is true.  */
+	  extract_range_for_var_from_comparison_expr (op0, code, op0, op1, &vr);
+	  if (old_vr->type == VR_RANGE || old_vr->type == VR_ANTI_RANGE)
+	    vrp_intersect_ranges (&vr, old_vr);
+
+	  /* If we found any usable VR, set the VR to ssa_name and create a
+	     PUSH old value in the stack with the old VR.  */
+	  if (vr.type == VR_RANGE || vr.type == VR_ANTI_RANGE)
+	    {
+	      new_vr = vrp_value_range_pool.allocate ();
+	      *new_vr = vr;
+	      push_value_range (op0, new_vr);
+	    }
+	}
+    }
+
+  /* Visit PHI stmts and discover any new VRs possible.  */
+  gimple_stmt_iterator gsi;
+  for (gphi_iterator gpi = gsi_start_phis (bb);
+       !gsi_end_p (gpi); gsi_next (&gpi))
+    {
+      gphi *phi = gpi.phi ();
+      if (stmt_interesting_for_vrp (phi))
+	{
+	  tree lhs = PHI_RESULT (phi);
+	  value_range vr_result = VR_INITIALIZER;
+	  /* See if the PHI has any back edges.  If there is any
+	     backedges we will have to set the lattice to
+	     VR_VARYING as we will not be traversing it till it
+	     reach fix point.  */
+	  if (visit_phi_node_p (phi))
+	    vrp_visit_phi_node_worker (phi, &vr_result);
+	  else
+	    set_value_range_to_varying (&vr_result);
+	  update_value_range (lhs, &vr_result);
+	}
+    }
+
+  /* Visit all other stmts and discover any new VRs possible.  */
+  for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+    {
+      gimple *stmt = gsi_stmt (gsi);
+      edge taken_edge;
+      tree output;
+      /* TODO, if found taken_edge, we should visit (return it) and travel
+	 again to improve VR as done in DOM/SCCVN optimizations.  It should
+	 be done carefully as stmts might prematurely leave a BB like
+	 in EH.  */
+      if (stmt_interesting_for_vrp (stmt))
+	{
+	  tree lhs = gimple_get_lhs (stmt);
+	  value_range vr = VR_INITIALIZER;
+	  vrp_visit_stmt_worker (stmt, &taken_edge, &output, &vr);
+	  update_value_range (lhs, &vr);
+
+	  /* Try folding stmts with the VR discovered.  */
+	  if (fold_stmt (&gsi, follow_single_use_edges))
+	    update_stmt (gsi_stmt (gsi));
+
+	  def_operand_p def_p = SINGLE_SSA_DEF_OPERAND (stmt, SSA_OP_DEF);
+	  /* Set the SSA with the value range.  */
+	  if (def_p
+	      && TREE_CODE (DEF_FROM_PTR (def_p)) == SSA_NAME
+	      && INTEGRAL_TYPE_P (TREE_TYPE (DEF_FROM_PTR (def_p))))
+	    {
+	      tree def = DEF_FROM_PTR (def_p);
+	      unsigned ver = SSA_NAME_VERSION (def);
+	      if ((vr_value[ver]->type == VR_RANGE
+		   || vr_value[ver]->type == VR_ANTI_RANGE)
+		  && (TREE_CODE (vr_value[ver]->min) == INTEGER_CST)
+		  && (TREE_CODE (vr_value[ver]->max) == INTEGER_CST))
+		set_range_info (def, vr_value[ver]->type, vr_value[ver]->min,
+				vr_value[ver]->max);
+	    }
+	}
+    }
+  return NULL;
+}
+
+/* Restore/pop VRs valid only for BB when we leave BB.  */
+
+void
+evrp_dom_walker::after_dom_children (basic_block bb ATTRIBUTE_UNUSED)
+{
+  gcc_checking_assert (!stack.is_empty ());
+  while (stack.last ().first != NULL_TREE)
+    pop_value_range (stack.last ().first);
+  pop_value_range (stack.last ().first);
+}
+
+/* Push the Value Range of VAR to the stack and update it with new VR.  */
+
+void
+evrp_dom_walker::push_value_range (const_tree var, value_range *vr)
+{
+  if (vr != NULL)
+    {
+      unsigned ver = SSA_NAME_VERSION (var);
+      gcc_checking_assert (vr_value);
+      stack.safe_push (std::make_pair (var, vr_value[ver]));
+
+      if (ver < num_vr_values)
+	vr_value[ver] = vr;
+    }
+  else
+    stack.safe_push (std::make_pair (var, vr));
+}
+
+/* Pop the Value Range from the vrp_stack and update VAR with it.  */
+
+value_range *
+evrp_dom_walker::pop_value_range (const_tree var)
+{
+  value_range *vr = stack.last ().second;
+  if (vr != NULL)
+    {
+      unsigned ver = SSA_NAME_VERSION (var);
+      gcc_checking_assert (var == stack.last ().first);
+      gcc_checking_assert (vr_value);
+
+      if (ver < num_vr_values)
+	vr_value[ver] = vr;
+    }
+  stack.pop ();
+  return vr;
+}
+
+
+/* Main entry point for the early vrp pass which is a simplified non-iterative
+   version of VRP where basic blocks are visited in dominance order.  Value
+   ranges discovered in early vrp will also be used by ipa-vrp.  */
+
+static unsigned int
+execute_early_vrp ()
+{
+  edge e;
+  edge_iterator ei;
+  basic_block bb;
+  early_vrp_p = true;
+
+  calculate_dominance_info (CDI_DOMINATORS);
+  FOR_EACH_BB_FN (bb, cfun)
+    {
+      FOR_EACH_EDGE (e, ei, bb->preds)
+	e->flags |= EDGE_EXECUTABLE;
+    }
+  vrp_initialize_lattice ();
+
+  /* Walk stmts in dominance order and propagate VRP.  */
+  evrp_dom_walker walker;
+  walker.walk (ENTRY_BLOCK_PTR_FOR_FN (cfun));
+  if (dump_file)
+    {
+      fprintf (dump_file, "\nValue ranges after Early VRP:\n\n");
+      dump_all_value_ranges (dump_file);
+      fprintf (dump_file, "\n");
+    }
+  vrp_free_lattice ();
+  early_vrp_p = false;
+  return 0;
 }
 
 
@@ -10546,9 +10812,11 @@ execute_vrp (bool warn_array_bounds_p)
   /* For visiting PHI nodes we need EDGE_DFS_BACK computed.  */
   mark_dfs_back_edges ();
 
+  vrp_initialize_lattice ();
   vrp_initialize ();
   ssa_propagate (vrp_visit_stmt, vrp_visit_phi_node);
   vrp_finalize (warn_array_bounds_p);
+  vrp_free_lattice ();
 
   free_numbers_of_iterations_estimates (cfun);
 
@@ -10646,3 +10914,44 @@ make_pass_vrp (gcc::context *ctxt)
 {
   return new pass_vrp (ctxt);
 }
+
+namespace {
+
+const pass_data pass_data_early_vrp =
+{
+  GIMPLE_PASS, /* type */
+  "evrp", /* name */
+  OPTGROUP_NONE, /* optinfo_flags */
+  TV_TREE_EARLY_VRP, /* tv_id */
+  PROP_ssa, /* properties_required */
+  0, /* properties_provided */
+  0, /* properties_destroyed */
+  0, /* todo_flags_start */
+  ( TODO_cleanup_cfg | TODO_update_ssa | TODO_verify_all ),
+};
+
+class pass_early_vrp : public gimple_opt_pass
+{
+public:
+  pass_early_vrp (gcc::context *ctxt)
+    : gimple_opt_pass (pass_data_early_vrp, ctxt)
+    {}
+
+  /* opt_pass methods: */
+  opt_pass * clone () { return new pass_early_vrp (m_ctxt); }
+  virtual bool gate (function *)
+    {
+      return flag_early_vrp != 0 && flag_tree_vrp != 0;
+    }
+  virtual unsigned int execute (function *)
+    { return execute_early_vrp (); }
+
+}; // class pass_vrp
+} // anon namespace
+
+gimple_opt_pass *
+make_pass_early_vrp (gcc::context *ctxt)
+{
+  return new pass_early_vrp (ctxt);
+}
+
-- 
2.7.4