[gcc r12-3969] Avoid CFG updates in VRP threader if nothing changed.

[gcc r12-3969] Avoid CFG updates in VRP threader if nothing changed.

[Aldy Hernandez]

https://gcc.gnu.org/g:77731cb8f3cfd2cc94219e03e7521822d679c6a4

commit r12-3969-g77731cb8f3cfd2cc94219e03e7521822d679c6a4
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Wed Sep 29 10:02:12 2021 +0200

    Avoid CFG updates in VRP threader if nothing changed.
    
    There is no need to update the CFG or SSAs if nothing has changed in VRP
    threading.
    
    gcc/ChangeLog:
    
            * tree-vrp.c (thread_through_all_blocks): Return bool.
            (execute_vrp_threader): Return TODO_* flags.
            (pass_data_vrp_threader): Set todo_flags_finish to 0.

Diff:
---
 gcc/tree-vrp.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index db9f3cd0a2f..69a3ab0ea9d 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -4372,9 +4372,9 @@ public:
   {
     walk (fun->cfg->x_entry_block_ptr);
   }
-  void thread_through_all_blocks ()
+  bool thread_through_all_blocks ()
   {
-    m_threader->thread_through_all_blocks (false);
+    return m_threader->thread_through_all_blocks (false);
   }
 
 private:
@@ -4438,7 +4438,8 @@ execute_vrp_threader (function *fun)
 {
   hybrid_threader threader;
   threader.thread_jumps (fun);
-  threader.thread_through_all_blocks ();
+  if (threader.thread_through_all_blocks ())
+    return (TODO_cleanup_cfg | TODO_update_ssa);
   return 0;
 }
 
@@ -4454,7 +4455,7 @@ const pass_data pass_data_vrp_threader =
   0, /* properties_provided */
   0, /* properties_destroyed */
   0, /* todo_flags_start */
-  ( TODO_cleanup_cfg | TODO_update_ssa ), /* todo_flags_finish */
+  0 /* todo_flags_finish */
 };
 
 class pass_vrp_threader : public gimple_opt_pass