From: Jan Hubicka <hubicka@ucw.cz>
To: gcc-patches@gcc.gnu.org
Subject: Add -Wsuggest-attribute=cold
Date: Mon, 24 Jul 2017 18:56:00 -0000 [thread overview]
Message-ID: <20170724185633.GA43541@kam.mff.cuni.cz> (raw)
Hi,
this patch adds -Wsuggest-attribute=cold because we can now statically detect
cold functions atuomatically.
Bootstrapped/regtested x86_64-linux. Plan to commit it tomorrow if there are no
complains.
Honza
* 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.
Index: common.opt
===================================================================
--- common.opt (revision 250470)
+++ common.opt (working copy)
@@ -708,6 +708,10 @@ 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)).
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi (revision 250470)
+++ doc/invoke.texi (working copy)
@@ -5172,7 +5172,7 @@ whether to issue a warning. Similarly t
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
@@ -5224,6 +5224,15 @@ might be appropriate for any function th
@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
Index: ipa-pure-const.c
===================================================================
--- ipa-pure-const.c (revision 250470)
+++ ipa-pure-const.c (working copy)
@@ -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
Index: predict.c
===================================================================
--- predict.c (revision 250470)
+++ predict.c (working copy)
@@ -3611,7 +3611,10 @@ 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;
@@ -3630,7 +3633,10 @@ 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))
Index: predict.h
===================================================================
--- predict.h (revision 250470)
+++ predict.h (working copy)
@@ -102,4 +102,7 @@ extern void propagate_unlikely_bbs_forwa
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 */
Index: testsuite/gcc.dg/cold-1.c
===================================================================
--- testsuite/gcc.dg/cold-1.c (revision 0)
+++ testsuite/gcc.dg/cold-1.c (working copy)
@@ -0,0 +1,21 @@
+/* { 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 ();
+}
next reply other threads:[~2017-07-24 18:56 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-24 18:56 Jan Hubicka [this message]
2017-07-24 19:02 ` Eric Gallager
2017-07-24 19:08 ` Jan Hubicka
2017-07-24 22:01 ` Jeff Law
2017-07-24 22:06 ` Jan Hubicka
2017-07-24 22:19 ` Jeff Law
2017-07-24 22:58 ` Martin Sebor
2017-10-09 11:42 ` Tom de Vries
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