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 --git a/gcc/tree-complex.cc b/gcc/tree-complex.cc
index dfb45b9d91cf4564777cae968433cfe656715d36..7480c07640e108222d2a9ce06098c1aacd9b641a 100644 (file)
--- 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);