On 07/26/2012 02:41 PM, Richard Henderson wrote:
> This is a patch...
... that I should have attached. Bah.
r~
gcc/
* doc/extend.texi (attribute): Document hot/cold for labels.
* predict.c (tree_estimate_probability_bb): Handle hot/cold
attributes on user labels.
* predict.def (PRED_HOT_LABEL, PRED_COLD_LABEL): New.
gcc/c-family/
* c-common.c (handle_hot_attribute): Allow labels.
(handle_cold_attribute): Likewise.
gcc/testsuite/
* gcc.dg/attr-hotcold-1.c: New.
* gcc.dg/tree-ssa/attr-hotcold-2.c: New.
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index b72506b..a002541 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -6169,7 +6169,8 @@ static tree
handle_hot_attribute (tree *node, tree name, tree ARG_UNUSED (args),
int ARG_UNUSED (flags), bool *no_add_attrs)
{
- if (TREE_CODE (*node) == FUNCTION_DECL)
+ if (TREE_CODE (*node) == FUNCTION_DECL
+ || TREE_CODE (*node) == LABEL_DECL)
{
if (lookup_attribute ("cold", DECL_ATTRIBUTES (*node)) != NULL)
{
@@ -6188,6 +6189,7 @@ handle_hot_attribute (tree *node, tree name, tree
ARG_UNUSED (args),
return NULL_TREE;
}
+
/* Handle a "cold" and attribute; arguments as in
struct attribute_spec.handler. */
@@ -6195,7 +6197,8 @@ static tree
handle_cold_attribute (tree *node, tree name, tree ARG_UNUSED (args),
int ARG_UNUSED (flags), bool *no_add_attrs)
{
- if (TREE_CODE (*node) == FUNCTION_DECL)
+ if (TREE_CODE (*node) == FUNCTION_DECL
+ || TREE_CODE (*node) == LABEL_DECL)
{
if (lookup_attribute ("hot", DECL_ATTRIBUTES (*node)) != NULL)
{
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index c3faf09..5d851a7 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -3345,33 +3345,53 @@ than 2.96.
@item hot
@cindex @code{hot} function attribute
-The @code{hot} attribute is used to inform the compiler that a function is a
-hot spot of the compiled program. The function is optimized more aggressively
-and on many target it is placed into special subsection of the text section so
-all hot functions appears close together improving locality.
+The @code{hot} attribute on a function is used to inform the compiler that
+the function is a hot spot of the compiled program. The function is
+optimized more aggressively and on many target it is placed into special
+subsection of the text section so all hot functions appears close together
+improving locality.
When profile feedback is available, via @option{-fprofile-use}, hot functions
are automatically detected and this attribute is ignored.
-The @code{hot} attribute is not implemented in GCC versions earlier
-than 4.3.
+The @code{hot} attribute on functions is not implemented in GCC versions
+earlier than 4.3.
+
+@cindex @code{hot} label attribute
+The @code{hot} attribute on a label is used to inform the compiler that
+path following the label are more likely than paths that are not so
+annotated. This attribute is used in cases where @code{__builtin_expect}
+cannot be used, for instance with computed goto or @code{asm goto}.
+
+The @code{hot} attribute on labels is not implemented in GCC versions
+earlier than 4.8.
@item cold
@cindex @code{cold} function attribute
-The @code{cold} attribute is used to inform the compiler that a function is
-unlikely executed. The function is optimized for size rather than speed and on
-many targets it is placed into special subsection of the text section so all
-cold functions appears close together improving code locality of non-cold parts
-of program. The paths leading to call of cold functions within code are marked
-as unlikely by the branch prediction mechanism. It is thus useful to mark
-functions used to handle unlikely conditions, such as @code{perror}, as cold to
-improve optimization of hot functions that do call marked functions in rare
-occasions.
-
-When profile feedback is available, via @option{-fprofile-use}, hot functions
+The @code{cold} attribute on functions is used to inform the compiler that
+the function is unlikely to be executed. The function is optimized for
+size rather than speed and on many targets it is placed into special
+subsection of the text section so all cold functions appears close together
+improving code locality of non-cold parts of program. The paths leading
+to call of cold functions within code are marked as unlikely by the branch
+prediction mechanism. It is thus useful to mark functions used to handle
+unlikely conditions, such as @code{perror}, as cold to improve optimization
+of hot functions that do call marked functions in rare occasions.
+
+When profile feedback is available, via @option{-fprofile-use}, cold functions
are automatically detected and this attribute is ignored.
-The @code{cold} attribute is not implemented in GCC versions earlier than 4.3.
+The @code{cold} attribute on functions is not implemented in GCC versions
+earlier than 4.3.
+
+@cindex @code{cold} label attribute
+The @code{cold} attribute on labels is used to inform the compiler that
+the path following the label is unlikely to be executed. This attribute
+is used in cases where @code{__builtin_expect} cannot be used, for instance
+with computed goto or @code{asm goto}.
+
+The @code{cold} attribute on labels is not implemented in GCC versions
+earlier than 4.8.
@item regparm (@var{number})
@cindex @code{regparm} attribute
diff --git a/gcc/predict.c b/gcc/predict.c
index b690bdc..b8acdba 100644
--- a/gcc/predict.c
+++ b/gcc/predict.c
@@ -2059,6 +2059,29 @@ tree_estimate_probability_bb (basic_block bb)
FOR_EACH_EDGE (e, ei, bb->succs)
{
+ /* Predict edges to user labels with attributes. */
+ if (e->dest != EXIT_BLOCK_PTR)
+ {
+ gimple_stmt_iterator gi;
+ for (gi = gsi_start_bb (e->dest); !gsi_end_p (gi); gsi_next (&gi))
+ {
+ gimple stmt = gsi_stmt (gi);
+ tree decl;
+
+ if (gimple_code (stmt) != GIMPLE_LABEL)
+ break;
+ decl = gimple_label_label (stmt);
+ if (DECL_ARTIFICIAL (decl))
+ continue;
+
+ /* Finally, we have a user-defined label. */
+ if (lookup_attribute ("cold", DECL_ATTRIBUTES (decl)))
+ predict_edge_def (e, PRED_COLD_LABEL, NOT_TAKEN);
+ else if (lookup_attribute ("hot", DECL_ATTRIBUTES (decl)))
+ predict_edge_def (e, PRED_HOT_LABEL, TAKEN);
+ }
+ }
+
/* Predict early returns to be probable, as we've already taken
care for error returns and other cases are often used for
fast paths through function.
diff --git a/gcc/predict.def b/gcc/predict.def
index 591bb1c..7e77f14 100644
--- a/gcc/predict.def
+++ b/gcc/predict.def
@@ -126,3 +126,10 @@ DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv
compare",
to set probability of branches that compares IV to loop bound variable. */
DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_VERY_LIKELY,
PRED_FLAG_FIRST_MATCH)
+
+/* Branches to hot labels are likely. */
+DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0)
+
+/* Branches to cold labels are extremely unlikely. */
+DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", PROB_VERY_LIKELY,
+ PRED_FLAG_FIRST_MATCH)
diff --git a/gcc/testsuite/gcc.dg/attr-hotcold-1.c
b/gcc/testsuite/gcc.dg/attr-hotcold-1.c
new file mode 100644
index 0000000..f63a95c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/attr-hotcold-1.c
@@ -0,0 +1,8 @@
+void f(void)
+{
+ goto A;
+ A: __attribute__((cold))
+ goto B;
+ B: __attribute__((hot))
+ return;
+}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/attr-hotcold-2.c
b/gcc/testsuite/gcc.dg/tree-ssa/attr-hotcold-2.c
new file mode 100644
index 0000000..84327fe
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/attr-hotcold-2.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-ipa-profile_estimate-details" } */
+
+void g(void);
+void h(void);
+void f(int x, int y)
+{
+ if (x) goto A;
+ if (y) goto B;
+ return;
+
+ A: __attribute__((cold))
+ g();
+ return;
+
+ B: __attribute__((hot))
+ h();
+ return;
+}
+
+/* { dg-final { scan-ipa-dump-times "block 4, loop depth 0, count 0, freq
1\[^0-9\]" 1 "profile_estimate" } } */
+
+/* Note: we're attempting to match some number > 6000, i.e. > 60%.
+ The exact number ought to be tweekable without having to juggle
+ the testcase around too much. */
+/* { dg-final { scan-ipa-dump-times "block 5, loop depth 0, count 0, freq
\[6-9\]\[0-9\]\[0-9\]\[0-9\]" 1 "profile_estimate" } } */
+
+/* { dg-final { cleanup-tree-dump "profile_estimate" } } */
