Only do switch bit test clustering when multiple labels point to same bb

The bit cluster code generation strategy is only beneficial when
multiple case labels point to the same code. Do a quick check if
that is the case before trying to cluster.

This fixes the switch part of PR117091 where all case labels are unique
however it doesn't address the performance problems for non unique
cases.

gcc/ChangeLog:

	PR middle-end/117091
	* gimple-if-to-switch.cc (if_chain::is_beneficial): Update
	find_bit_test call.
	* tree-switch-conversion.cc (bit_test_cluster::find_bit_tests):
	Get max_c argument and bail out early if all case labels are
	unique.
	(switch_decision_tree::compute_cases_per_edge): Record number of
	targets per label and return.
	(switch_decision_tree::analyze_switch_statement): ... pass to
	find_bit_tests.
	* tree-switch-conversion.h: Update prototypes.

diff --git a/gcc/gimple-if-to-switch.cc b/gcc/gimple-if-to-switch.cc
index 4246e12606f97875b1b1580aa74adf589be294d4..8f71f43864f0156e24df1021fe26cb885ef5b118 100644 (file)
--- a/gcc/gimple-if-to-switch.cc
+++ b/gcc/gimple-if-to-switch.cc
@@ -255,7 +255,7 @@ if_chain::is_beneficial ()
   else
     output.release ();
 
-  output = bit_test_cluster::find_bit_tests (filtered_clusters);
+  output = bit_test_cluster::find_bit_tests (filtered_clusters, 2);
   r = output.length () < filtered_clusters.length ();
   if (r)
     dump_clusters (&output, "BT can be built");

diff --git a/gcc/tree-switch-conversion.cc b/gcc/tree-switch-conversion.cc
index 33023875ef97e3b717d08b0670d95fb47f6b181d..852419b2f4becc6407007a1aca4d9984b8c8a095 100644 (file)
--- a/gcc/tree-switch-conversion.cc
+++ b/gcc/tree-switch-conversion.cc
@@ -1773,12 +1773,13 @@ jump_table_cluster::is_beneficial (const vec<cluster *> &,
 }
 
 /* Find bit tests of given CLUSTERS, where all members of the vector
-   are of type simple_cluster.  New clusters are returned.  */
+   are of type simple_cluster.   MAX_C is the approx max number of cases per
+   label.  New clusters are returned.  */
 
 vec<cluster *>
-bit_test_cluster::find_bit_tests (vec<cluster *> &clusters)
+bit_test_cluster::find_bit_tests (vec<cluster *> &clusters, int max_c)
 {
-  if (!is_enabled ())
+  if (!is_enabled () || max_c == 1)
     return clusters.copy ();
 
   unsigned l = clusters.length ();
@@ -2207,18 +2208,26 @@ bit_test_cluster::hoist_edge_and_branch_if_true (gimple_stmt_iterator *gsip,
 }
 
 /* Compute the number of case labels that correspond to each outgoing edge of
-   switch statement.  Record this information in the aux field of the edge.  */
+   switch statement.  Record this information in the aux field of the edge.
+   Return the approx max number of cases per edge.  */
 
-void
+int
 switch_decision_tree::compute_cases_per_edge ()
 {
+  int max_c = 0;
   reset_out_edges_aux (m_switch);
   int ncases = gimple_switch_num_labels (m_switch);
   for (int i = ncases - 1; i >= 1; --i)
     {
       edge case_edge = gimple_switch_edge (cfun, m_switch, i);
       case_edge->aux = (void *) ((intptr_t) (case_edge->aux) + 1);
+      /* For a range case add one extra. That's enough for the bit
+        cluster heuristic.  */
+      if ((intptr_t)case_edge->aux > max_c)
+       max_c = (intptr_t)case_edge->aux +
+               !!CASE_HIGH (gimple_switch_label (m_switch, i));
     }
+  return max_c;
 }
 
 /* Analyze switch statement and return true when the statement is expanded
@@ -2236,7 +2245,7 @@ switch_decision_tree::analyze_switch_statement ()
   m_case_bbs.reserve (l);
   m_case_bbs.quick_push (default_bb);
 
-  compute_cases_per_edge ();
+  int max_c = compute_cases_per_edge ();
 
   for (unsigned i = 1; i < l; i++)
     {
@@ -2257,7 +2266,7 @@ switch_decision_tree::analyze_switch_statement ()
   reset_out_edges_aux (m_switch);
 
   /* Find bit-test clusters.  */
-  vec<cluster *> output = bit_test_cluster::find_bit_tests (clusters);
+  vec<cluster *> output = bit_test_cluster::find_bit_tests (clusters, max_c);
 
   /* Find jump table clusters.  */
   vec<cluster *> output2;

diff --git a/gcc/tree-switch-conversion.h b/gcc/tree-switch-conversion.h
index 6468995eb31667602b4320feca5b0dc43121c656..e6a85fa602588df19595716785ccd2021d0a3205 100644 (file)
--- a/gcc/tree-switch-conversion.h
+++ b/gcc/tree-switch-conversion.h
@@ -399,7 +399,7 @@ public:
 
   /* Find bit tests of given CLUSTERS, where all members of the vector
      are of type simple_cluster.  New clusters are returned.  */
-  static vec<cluster *> find_bit_tests (vec<cluster *> &clusters);
+  static vec<cluster *> find_bit_tests (vec<cluster *> &clusters, int max_c);
 
   /* Return true when RANGE of case values with UNIQ labels
      can build a bit test.  */
@@ -576,8 +576,9 @@ public:
   bool try_switch_expansion (vec<cluster *> &clusters);
   /* Compute the number of case labels that correspond to each outgoing edge of
      switch statement.  Record this information in the aux field of the edge.
+     Returns approx max number of cases per edge.
      */
-  void compute_cases_per_edge ();
+  int compute_cases_per_edge ();
 
   /* Before switch transformation, record all SSA_NAMEs defined in switch BB
      and used in a label basic block.  */