[gcc r15-3128] tree-optimization/116463 - complex lowering leaves around dead stmts

[Richard Biener via Gcc-cvs]

https://gcc.gnu.org/g:de1923f9f4d5344694c22ca883aeb15caf635734

commit r15-3128-gde1923f9f4d5344694c22ca883aeb15caf635734
Author: Richard Biener <rguent...@suse.de>
Date:   Fri Aug 23 13:44:29 2024 +0200

    tree-optimization/116463 - complex lowering leaves around dead stmts
    
    Complex lowering generally replaces existing complex defs with
    COMPLEX_EXPRs but those might be dead when it can always refer to
    components from the lattice.  This in turn can pessimize followup
    transforms like forwprop and reassoc, the following makes sure to
    get rid of dead COMPLEX_EXPRs generated by using
    simple_dce_from_worklist.
    
            PR tree-optimization/116463
            * tree-complex.cc: Include tree-ssa-dce.h.
            (dce_worklist): New global.
            (update_complex_assignment): Add SSA def to the DCE worklist.
            (tree_lower_complex): Perform DCE.

Diff:
---
 gcc/tree-complex.cc | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/gcc/tree-complex.cc b/gcc/tree-complex.cc
index dfb45b9d91cf..7480c07640e1 100644
--- a/gcc/tree-complex.cc
+++ b/gcc/tree-complex.cc
@@ -46,6 +46,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "case-cfn-macros.h"
 #include "builtins.h"
 #include "optabs-tree.h"
+#include "tree-ssa-dce.h"
 
 /* For each complex ssa name, a lattice value.  We're interested in finding
    out whether a complex number is degenerate in some way, having only real
@@ -88,6 +89,9 @@ static vec<gphi *> phis_to_revisit;
 /* BBs that need EH cleanup.  */
 static bitmap need_eh_cleanup;
 
+/* SSA defs we should try to DCE.  */
+static bitmap dce_worklist;
+
 /* Lookup UID in the complex_variable_components hashtable and return the
    associated tree.  */
 static tree
@@ -731,6 +735,7 @@ update_complex_assignment (gimple_stmt_iterator *gsi, tree 
r, tree i)
   update_stmt (stmt);
   if (maybe_clean_or_replace_eh_stmt (old_stmt, stmt))
     bitmap_set_bit (need_eh_cleanup, gimple_bb (stmt)->index);
+  bitmap_set_bit (dce_worklist, SSA_NAME_VERSION (gimple_assign_lhs (stmt)));
 
   update_complex_components (gsi, gsi_stmt (*gsi), r, i);
 }
@@ -1962,6 +1967,7 @@ tree_lower_complex (void)
   complex_propagate.ssa_propagate ();
 
   need_eh_cleanup = BITMAP_ALLOC (NULL);
+  dce_worklist = BITMAP_ALLOC (NULL);
 
   complex_variable_components = new int_tree_htab_type (10);
 
@@ -2008,6 +2014,9 @@ tree_lower_complex (void)
 
   gsi_commit_edge_inserts ();
 
+  simple_dce_from_worklist (dce_worklist, need_eh_cleanup);
+  BITMAP_FREE (dce_worklist);
+
   unsigned todo
     = gimple_purge_all_dead_eh_edges (need_eh_cleanup) ? TODO_cleanup_cfg : 0;
   BITMAP_FREE (need_eh_cleanup);