[Bug middle-end/117091] switch clustering takes extensive time with large switches even at -O0

[ak at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117091

--- Comment #4 from ak at gcc dot gnu.org ---
Here's a patch that enables the slow switch conversions only at -O2.
With that the test case builds reasonably quickly. 

diff --git a/gcc/common.opt b/gcc/common.opt
index 12b25ff486de..4af7a94fea42 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2189,11 +2189,11 @@ Common Var(flag_ivopts) Init(1) Optimization
 Optimize induction variables on trees.

 fjump-tables
-Common Var(flag_jump_tables) Init(1) Optimization
+Common Var(flag_jump_tables) Init(-1) Optimization
 Use jump tables for sufficiently large switch statements.

 fbit-tests
-Common Var(flag_bit_tests) Init(1) Optimization
+Common Var(flag_bit_tests) Init(-1) Optimization
 Use bit tests for sufficiently large switch statements.

 fkeep-inline-functions
diff --git a/gcc/tree-switch-conversion.h b/gcc/tree-switch-conversion.h
index 6468995eb316..1cca23671d70 100644
--- a/gcc/tree-switch-conversion.h
+++ b/gcc/tree-switch-conversion.h
@@ -442,7 +442,7 @@ public:
   /* Return whether bit test expansion is allowed.  */
   static inline bool is_enabled (void)
   {
-    return flag_bit_tests;
+    return flag_bit_tests >= 0 ? flag_bit_tests : (optimize > 1);
   }

   /* True when the jump table handles an entire switch statement.  */
@@ -524,7 +524,8 @@ bool jump_table_cluster::is_enabled (void)
      over-ruled us, we really have no choice.  */
   if (!targetm.have_casesi () && !targetm.have_tablejump ())
     return false;
-  if (!flag_jump_tables)
+  int flag = flag_jump_tables >= 0 ? flag_jump_tables : (optimize > 1);
+  if (!flag)
     return false;
 #ifndef ASM_OUTPUT_ADDR_DIFF_ELT
   if (flag_pic)