invoke.texi (Wsuggest-attribute=cold): Document.

	* invoke.texi (Wsuggest-attribute=cold): Document.
	* common.opt (Wsuggest-attribute=cold): New
	* ipa-pure-const.c (warn_function_cold): New function.
	* predict.c (compute_function_frequency): Use it.
	* predict.h (warn_function_cold): Declare.

	* gcc.dg/cold-1.c: New testcase.

From-SVN: r253513

gcc/ChangeLog

+2017-10-07  Jan Hubicka  <hubicka@ucw.cz>
+
+	* invoke.texi (Wsuggest-attribute=cold): Document.
+	* common.opt (Wsuggest-attribute=cold): New
+	* ipa-pure-const.c (warn_function_cold): New function.
+	* predict.c (compute_function_frequency): Use it.
+	* predict.h (warn_function_cold): Declare.
+
 2017-10-06  Jan Hubicka  <hubicka@ucw.cz>
 
 	* tree-switch-conversion.c (do_jump_if_equal, emit_cmp_and_jump_insns):

gcc/common.opt

@@ -721,6 +721,10 @@ Wstrict-overflow=
 Common Joined RejectNegative UInteger Var(warn_strict_overflow) Warning
 Warn about optimizations that assume that signed overflow is undefined.
 
+Wsuggest-attribute=cold
+Common Var(warn_suggest_attribute_cold) Warning
+Warn about functions which might be candidates for __attribute__((cold)).
+
 Wsuggest-attribute=const
 Common Var(warn_suggest_attribute_const) Warning
 Warn about functions which might be candidates for __attribute__((const)).

gcc/doc/invoke.texi

@@ -5201,7 +5201,7 @@ whether to issue a warning.  Similarly to @option{-Wstringop-overflow=3} this
 setting of the option may result in warnings for benign code.
 @end table
 
-@item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]}
+@item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}cold@r{]}
 @opindex Wsuggest-attribute=
 @opindex Wno-suggest-attribute=
 Warn for cases where adding an attribute may be beneficial. The
@@ -5253,6 +5253,15 @@ might be appropriate for any function that calls a function like
 @code{vprintf} or @code{vscanf}, but this might not always be the
 case, and some functions for which @code{format} attributes are
 appropriate may not be detected.
+
+@item -Wsuggest-attribute=cold
+@opindex Wsuggest-attribute=cold
+@opindex Wno-suggest-attribute=cold
+
+Warn about functions that might be candidates for @code{cold} attribute.  This
+is based on static detection and generally will only warn about functions which
+always leads to a call to another @code{cold} function such as wrappers of
+C++ @code{throw} or fatal error reporting functions leading to @code{abort}.
 @end table
 
 @item -Wsuggest-final-types

gcc/ipa-pure-const.c

@@ -156,7 +156,8 @@ private:
 static bool
 function_always_visible_to_compiler_p (tree decl)
 {
-  return (!TREE_PUBLIC (decl) || DECL_DECLARED_INLINE_P (decl));
+  return (!TREE_PUBLIC (decl) || DECL_DECLARED_INLINE_P (decl)
+	  || DECL_COMDAT (decl));
 }
 
 /* Emit suggestion about attribute ATTRIB_NAME for DECL.  KNOWN_FINITE
@@ -232,6 +233,21 @@ warn_function_noreturn (tree decl)
 			   true, warned_about, "noreturn");
 }
 
+void
+warn_function_cold (tree decl)
+{
+  tree original_decl = decl;
+
+  cgraph_node *node = cgraph_node::get (decl);
+  if (node->instrumentation_clone)
+    decl = node->instrumented_version->decl;
+
+  static hash_set<tree> *warned_about;
+  warned_about 
+    = suggest_attribute (OPT_Wsuggest_attribute_cold, original_decl,
+			 true, warned_about, "cold");
+}
+
 /* Return true if we have a function state for NODE.  */
 
 static inline bool
@@ -1788,6 +1804,7 @@ pass_local_pure_const::execute (function *fun)
 
   node = cgraph_node::get (current_function_decl);
   skip = skip_function_for_local_pure_const (node);
+
   if (!warn_suggest_attribute_const
       && !warn_suggest_attribute_pure
       && skip)

gcc/predict.c

@@ -3613,7 +3613,10 @@ compute_function_frequency (void)
       if (ENTRY_BLOCK_PTR_FOR_FN (cfun)->count == profile_count::zero ()
 	  || lookup_attribute ("cold", DECL_ATTRIBUTES (current_function_decl))
 	     != NULL)
-        node->frequency = NODE_FREQUENCY_UNLIKELY_EXECUTED;
+	{
+          node->frequency = NODE_FREQUENCY_UNLIKELY_EXECUTED;
+	  warn_function_cold (current_function_decl);
+	}
       else if (lookup_attribute ("hot", DECL_ATTRIBUTES (current_function_decl))
 	       != NULL)
         node->frequency = NODE_FREQUENCY_HOT;
@@ -3632,7 +3635,10 @@ compute_function_frequency (void)
      Ipa-profile pass will drop functions only called from unlikely
      functions to unlikely and that is most of what we care about.  */
   if (!cfun->after_inlining)
-    node->frequency = NODE_FREQUENCY_UNLIKELY_EXECUTED;
+    {
+      node->frequency = NODE_FREQUENCY_UNLIKELY_EXECUTED;
+      warn_function_cold (current_function_decl);
+    }
   FOR_EACH_BB_FN (bb, cfun)
     {
       if (maybe_hot_bb_p (cfun, bb))

gcc/predict.h

@@ -102,4 +102,7 @@ extern void propagate_unlikely_bbs_forward (void);
 
 extern void add_reg_br_prob_note (rtx_insn *, profile_probability);
 
+/* In ipa-pure-const.c   */
+extern void warn_function_cold (tree);
+
 #endif  /* GCC_PREDICT_H */

gcc/testsuite/ChangeLog

+2017-10-07  Jan Hubicka  <hubicka@ucw.cz>
+
+	* gcc.dg/cold-1.c: New testcase.
+
 2017-10-07  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/80805

gcc/testsuite/gcc.dg/cold-1.c

+/* { dg-do compile { target nonpic } } */
+/* { dg-options "-O2 -Wsuggest-attribute=cold" } */
+
+extern void do_something_interesting_and_never_return ();
+
+int
+foo1(int a)  
+{ /* { dg-warning "cold" "detect cold candidate" { target *-*-* } "8" } */ 
+  if (a)
+    abort ();
+  else
+    abort ();
+}
+
+int
+foo2(int a)  
+{ 
+  if (a)
+    do_something_interesting_and_never_return ();
+  abort ();
+}