Propagate value ranges of return values

[Jan Hubicka <hubicka@ucw.cz>]

Hi,
this patch implements very basic propaation of return value ranges from VRP
pass.  This helps std::vector's push_back since we work out value range of
allocated block.  This propagates only within single translation unit.  I hoped
we will also do the propagation at WPA stage, but that needs more work on
ipa-cp side.

I also added code auto-detecting return_nonnull and corresponding -Wsuggest-attribute

Variant of this patch bootstrapped/regtested x86_64-linux, testing with
this version is running.  I plan to commit the patch at Monday provided
there are no issues.

gcc/ChangeLog:

	* cgraph.cc (add_detected_attribute_1): New function.
	(cgraph_node::add_detected_attribute): New member function.
	* cgraph.h (struct cgraph_node): Declare it.
	* common.opt: Add Wsuggest-attribute=returns_nonnull.
	* doc/invoke.texi: Document +Wsuggest-attribute=returns_nonnull.
	* gimple-range-fold.cc: Include ipa-prop and dependencies.
	(fold_using_range::range_of_call): Look for return value range.
	* ipa-prop.cc (struct ipa_return_value_summary): New structure.
	(class ipa_return_value_sum_t): New summary.
	(ipa_record_return_value_range): New function.
	(ipa_return_value_range): New function.
	* ipa-prop.h (ipa_return_value_range): Declare.
	(ipa_record_return_value_range): Declare.
	* ipa-pure-const.cc (warn_function_returns_nonnull): New function.
	* ipa-utils.h (warn_function_returns_nonnull): Declare.
	* symbol-summary.h: Fix comment typo.
	* tree-vrp.cc (execute_ranger_vrp): Record return values.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/return-value-range-1.c: New test.

diff --git a/gcc/cgraph.cc b/gcc/cgraph.cc
index e41e5ad3ae7..71dacf23ce1 100644
--- a/gcc/cgraph.cc
+++ b/gcc/cgraph.cc
@@ -2629,6 +2629,54 @@ cgraph_node::set_malloc_flag (bool malloc_p)
   return changed;
 }
 
+/* Worker to set malloc flag.  */
+static void
+add_detected_attribute_1 (cgraph_node *node, const char *attr, bool *changed)
+{
+  if (!lookup_attribute (attr, DECL_ATTRIBUTES (node->decl)))
+    {
+      DECL_ATTRIBUTES (node->decl) = tree_cons (get_identifier (attr),
+					 NULL_TREE, DECL_ATTRIBUTES (node->decl));
+      *changed = true;
+    }
+
+  ipa_ref *ref;
+  FOR_EACH_ALIAS (node, ref)
+    {
+      cgraph_node *alias = dyn_cast<cgraph_node *> (ref->referring);
+      if (alias->get_availability () > AVAIL_INTERPOSABLE)
+	add_detected_attribute_1 (alias, attr, changed);
+    }
+
+  for (cgraph_edge *e = node->callers; e; e = e->next_caller)
+    if (e->caller->thunk
+	&& (e->caller->get_availability () > AVAIL_INTERPOSABLE))
+      add_detected_attribute_1 (e->caller, attr, changed);
+}
+
+/* Set DECL_IS_MALLOC on NODE's decl and on NODE's aliases if any.  */
+
+bool
+cgraph_node::add_detected_attribute (const char *attr)
+{
+  bool changed = false;
+
+  if (get_availability () > AVAIL_INTERPOSABLE)
+    add_detected_attribute_1 (this, attr, &changed);
+  else
+    {
+      ipa_ref *ref;
+
+      FOR_EACH_ALIAS (this, ref)
+	{
+	  cgraph_node *alias = dyn_cast<cgraph_node *> (ref->referring);
+	  if (alias->get_availability () > AVAIL_INTERPOSABLE)
+	    add_detected_attribute_1 (alias, attr, &changed);
+	}
+    }
+  return changed;
+}
+
 /* Worker to set noreturng flag.  */
 static void
 set_noreturn_flag_1 (cgraph_node *node, bool noreturn_p, bool *changed)
diff --git a/gcc/cgraph.h b/gcc/cgraph.h
index cedaaac3a45..cfdd9f693a8 100644
--- a/gcc/cgraph.h
+++ b/gcc/cgraph.h
@@ -1190,6 +1190,10 @@ struct GTY((tag ("SYMTAB_FUNCTION"))) cgraph_node : public symtab_node
 
   bool set_pure_flag (bool pure, bool looping);
 
+  /* Add attribute ATTR to cgraph_node's decl and on aliases of the node
+     if any.  */
+  bool add_detected_attribute (const char *attr);
+
   /* Call callback on function and aliases associated to the function.
      When INCLUDE_OVERWRITABLE is false, overwritable aliases and thunks are
      skipped. */
diff --git a/gcc/common.opt b/gcc/common.opt
index d21db5d4a20..0be4f02677c 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -781,6 +781,10 @@ Wsuggest-attribute=malloc
 Common Var(warn_suggest_attribute_malloc) Warning
 Warn about functions which might be candidates for __attribute__((malloc)).
 
+Wsuggest-attribute=returns_nonnull
+Common Var(warn_suggest_attribute_malloc) Warning
+Warn about functions which might be candidates for __attribute__((malloc)).
+
 Wsuggest-final-types
 Common Var(warn_suggest_final_types) Warning
 Warn about C++ polymorphic types where adding final keyword would improve code quality.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 557d613a1e6..b9e98843613 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -8092,7 +8092,7 @@ if the array is referenced as a flexible array member.
 
 @opindex Wsuggest-attribute=
 @opindex Wno-suggest-attribute=
-@item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}cold@r{|}malloc@r{]}
+@item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}cold@r{|}malloc@r{]}returns_nonnull@r{|}
 Warn for cases where adding an attribute may be beneficial. The
 attributes currently supported are listed below.
 
@@ -8112,9 +8112,11 @@ attributes currently supported are listed below.
 @itemx -Wsuggest-attribute=noreturn
 @itemx -Wmissing-noreturn
 @itemx -Wsuggest-attribute=malloc
+@itemx -Wsuggest-attribute=returns_nonnull
+@itemx -Wno-suggest-attribute=returns_nonnull
 
 Warn about functions that might be candidates for attributes
-@code{pure}, @code{const} or @code{noreturn} or @code{malloc}. The compiler
+@code{pure}, @code{const}, @code{noreturn}, @code{malloc} or @code{returns_nonnull}. The compiler
 only warns for functions visible in other compilation units or (in the case of
 @code{pure} and @code{const}) if it cannot prove that the function returns
 normally. A function returns normally if it doesn't contain an infinite loop or
diff --git a/gcc/gimple-range-fold.cc b/gcc/gimple-range-fold.cc
index 6e9530c3d7f..0af3fa1b008 100644
--- a/gcc/gimple-range-fold.cc
+++ b/gcc/gimple-range-fold.cc
@@ -44,6 +44,11 @@ along with GCC; see the file COPYING3.  If not see
 #include "value-query.h"
 #include "gimple-range-op.h"
 #include "gimple-range.h"
+#include "cgraph.h"
+#include "alloc-pool.h"
+#include "symbol-summary.h"
+#include "ipa-utils.h"
+#include "ipa-prop.h"
 // Construct a fur_source, and set the m_query field.
 
 fur_source::fur_source (range_query *q)
@@ -1013,6 +1018,24 @@ fold_using_range::range_of_call (vrange &r, gcall *call, fur_source &)
   else
     r.set_varying (type);
 
+  tree callee = gimple_call_fndecl (call);
+  if (callee)
+    {
+      Value_Range val;
+      if (ipa_return_value_range (val, callee))
+	{
+	  r.intersect (val);
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "Using return value range of ");
+	      print_generic_expr (dump_file, callee, TDF_SLIM);
+	      fprintf (dump_file, ": ");
+	      val.dump (dump_file);
+	      fprintf (dump_file, "\n");
+	    }
+	}
+    }
+
   // If there is an LHS, intersect that with what is known.
   if (lhs)
     {
diff --git a/gcc/ipa-prop.cc b/gcc/ipa-prop.cc
index 7de2b788185..e77bc9c340b 100644
--- a/gcc/ipa-prop.cc
+++ b/gcc/ipa-prop.cc
@@ -237,6 +237,35 @@ gt_ggc_mx (ipa_vr *&x)
   return gt_ggc_mx ((ipa_vr *) x);
 }
 
+/* Analysis summery of function call return value.  */
+struct GTY(()) ipa_return_value_summary
+{
+  /* Known value range.
+     This needs to be wrapped in struccture due to specific way
+     we allocate ipa_vr. */
+  ipa_vr *vr;
+};
+
+/* Function summary for return values.  */
+class ipa_return_value_sum_t : public function_summary <ipa_return_value_summary *>
+{
+public:
+  ipa_return_value_sum_t (symbol_table *table, bool ggc):
+    function_summary <ipa_return_value_summary *> (table, ggc) { }
+
+  /* Hook that is called by summary when a node is duplicated.  */
+  void duplicate (cgraph_node *,
+		  cgraph_node *,
+		  ipa_return_value_summary *data,
+		  ipa_return_value_summary *data2) final override
+  {
+    *data2=*data;
+  }
+};
+
+/* Variable hoding the return value summary.  */
+static GTY(()) function_summary <ipa_return_value_summary *> *ipa_return_value_sum;
+
 
 /* Return true if DECL_FUNCTION_SPECIFIC_OPTIMIZATION of the decl associated
    with NODE should prevent us from analyzing it for the purposes of IPA-CP.  */
@@ -5915,5 +5944,49 @@ ipcp_transform_function (struct cgraph_node *node)
   return modified_mem_access ? TODO_update_ssa_only_virtuals : 0;
 }
 
+/* Record that current function return value range is VAL.  */
+
+void
+ipa_record_return_value_range (Value_Range val)
+{
+  cgraph_node *n = cgraph_node::get (current_function_decl);
+  if (!ipa_return_value_sum)
+    {
+      if (!ipa_vr_hash_table)
+	ipa_vr_hash_table = hash_table<ipa_vr_ggc_hash_traits>::create_ggc (37);
+      ipa_return_value_sum = new (ggc_alloc_no_dtor <ipa_return_value_sum_t> ())
+	      ipa_return_value_sum_t (symtab, true);
+      ipa_return_value_sum->disable_insertion_hook ();
+    }
+  ipa_return_value_sum->get_create (n)->vr = ipa_get_value_range (val);
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fprintf (dump_file, "Recording return range ");
+      val.dump (dump_file);
+      fprintf (dump_file, "\n");
+    }
+}
+
+/* Return true if value range of DECL is known and if so initialize RANGE.  */
+
+bool
+ipa_return_value_range (Value_Range &range, tree decl)
+{
+  cgraph_node *n = cgraph_node::get (decl);
+  if (!n || !ipa_return_value_sum)
+    return false;
+  enum availability avail;
+  n = n->ultimate_alias_target (&avail);
+  if (avail < AVAIL_AVAILABLE)
+    return false;
+  if (n->decl != decl && !useless_type_conversion_p (TREE_TYPE (decl), TREE_TYPE (n->decl)))
+    return false;
+  ipa_return_value_summary *v = ipa_return_value_sum->get (n);
+  if (!v)
+    return false;
+  v->vr->get_vrange (range);
+  return true;
+}
+
 
 #include "gt-ipa-prop.h"
diff --git a/gcc/ipa-prop.h b/gcc/ipa-prop.h
index fcd0e5c638f..5901c805c40 100644
--- a/gcc/ipa-prop.h
+++ b/gcc/ipa-prop.h
@@ -309,7 +309,7 @@ public:
   void get_vrange (Value_Range &) const;
   bool equal_p (const vrange &) const;
   const vrange_storage *storage () const { return m_storage; }
-  void streamer_read (lto_input_block *, data_in *);
+  void streamer_read (lto_input_block *, class data_in *);
   void streamer_write (output_block *) const;
   void dump (FILE *) const;
 
@@ -1274,4 +1274,7 @@ ipa_range_set_and_normalize (vrange &r, tree val)
     r.set (val, val);
 }
 
+bool ipa_return_value_range (Value_Range &range, tree decl);
+void ipa_record_return_value_range (Value_Range val);
+
 #endif /* IPA_PROP_H */
diff --git a/gcc/ipa-pure-const.cc b/gcc/ipa-pure-const.cc
index 058a7dd3019..3060ffeefcd 100644
--- a/gcc/ipa-pure-const.cc
+++ b/gcc/ipa-pure-const.cc
@@ -292,6 +292,15 @@ warn_function_cold (tree decl)
 			 true, warned_about, "cold");
 }
 
+void
+warn_function_returns_nonnull (tree decl)
+{
+  static hash_set<tree> *warned_about;
+  warned_about
+    = suggest_attribute (OPT_Wsuggest_attribute_returns_nonnull, decl,
+			 true, warned_about, "returns_nonnull");
+}
+
 /* Check to see if the use (or definition when CHECKING_WRITE is true)
    variable T is legal in a function that is either pure or const.  */
 
diff --git a/gcc/ipa-utils.h b/gcc/ipa-utils.h
index 0eefcf40d44..84728c589ea 100644
--- a/gcc/ipa-utils.h
+++ b/gcc/ipa-utils.h
@@ -105,6 +105,7 @@ tree prevailing_odr_type (tree type);
 void enable_odr_based_tbaa (tree type);
 bool odr_based_tbaa_p (const_tree type);
 void set_type_canonical_for_odr_type (tree type, tree canonical);
+void warn_function_returns_nonnull (tree);
 
 void register_odr_enum (tree type);
 
diff --git a/gcc/symbol-summary.h b/gcc/symbol-summary.h
index 3ed61627382..5fd49a2552e 100644
--- a/gcc/symbol-summary.h
+++ b/gcc/symbol-summary.h
@@ -71,7 +71,7 @@ public:
 	= m_symtab->add_cgraph_insertion_hook (m_symtab_insertion, this);
   }
 
-  /* Enable insertion hook invocation.  */
+  /* Disable insertion hook invocation.  */
   void disable_insertion_hook ()
   {
     if (m_symtab_insertion_hook != NULL)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/return-value-range-1.c b/gcc/testsuite/gcc.dg/tree-ssa/return-value-range-1.c
new file mode 100644
index 00000000000..4db52233c5d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/return-value-range-1.c
@@ -0,0 +1,22 @@
+/* { dg-do ling } */
+/* { dg-options "-O1 -dump-tree-evrp-details" } */
+__attribute__ ((__noinline__))
+int a(char c)
+{
+	return c;
+}
+void link_error ();
+
+void
+test(int d)
+{
+	if (a(d) > 200)
+		link_error ();
+}
+int
+main(int argc, char **argv)
+{
+	test(argc);
+	return 0;
+}
+/* { dg-final { scan-tree-dump-times "Recording return range" 2 "evrp"} } */
diff --git a/gcc/tree-vrp.cc b/gcc/tree-vrp.cc
index 917fa873714..11a382170d8 100644
--- a/gcc/tree-vrp.cc
+++ b/gcc/tree-vrp.cc
@@ -52,6 +52,11 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-fold.h"
 #include "tree-dfa.h"
 #include "tree-ssa-dce.h"
+#include "alloc-pool.h"
+#include "cgraph.h"
+#include "symbol-summary.h"
+#include "ipa-utils.h"
+#include "ipa-prop.h"
 
 // This class is utilized by VRP and ranger to remove __builtin_unreachable
 // calls, and reflect any resulting global ranges.
@@ -1081,6 +1086,47 @@ execute_ranger_vrp (struct function *fun, bool warn_array_bounds_p,
       array_checker.check ();
     }
 
+
+  if (Value_Range::supports_type_p (TREE_TYPE (TREE_TYPE (current_function_decl))))
+    {
+      edge e;
+      edge_iterator ei;
+      bool found = false;
+      Value_Range return_range (TREE_TYPE (TREE_TYPE (current_function_decl)));
+      FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR_FOR_FN (cfun)->preds)
+	if (greturn *ret = dyn_cast <greturn *> (*gsi_last_bb (e->src)))
+	  {
+	    tree retval = gimple_return_retval (ret);
+	    if (!retval)
+	      {
+		return_range.set_varying (TREE_TYPE (TREE_TYPE (current_function_decl)));
+		found = true;
+		continue;
+	      }
+	    Value_Range r (TREE_TYPE (retval));
+	    if (ranger->range_of_expr (r, retval, ret)
+		&& !r.undefined_p ()
+		&& !r.varying_p ())
+	      {
+		if (!found)
+		  return_range = r;
+		else
+		  return_range.union_ (r);
+	      }
+	    else
+	      return_range.set_varying (TREE_TYPE (retval));
+	    found = true;
+	  }
+      if (found && !return_range.varying_p ())
+	{
+	  ipa_record_return_value_range (return_range);
+	  if (POINTER_TYPE_P (TREE_TYPE (TREE_TYPE (current_function_decl)))
+	      && return_range.nonzero_p ()
+	      && cgraph_node::get (current_function_decl)->add_detected_attribute ("returns_nonnull"))
+	    warn_function_returns_nonnull (current_function_decl);
+	}
+    }
+
   phi_analysis_finalize ();
   disable_ranger (fun);
   scev_finalize ();