[PATCH] Update SSA_NAME manager to use two lists

	* gimple-ssa.h (gimple_df): Add free_ssanames_queue field.
	* passes.c: Include tree-ssanames.h.
	(execute_function_todo): Flush the pending free SSA_NAMEs after
	eliminating unreachable basic blocks.
	* tree-ssanames.c (FREE_SSANAMES_QUEUE): new.
	(init_ssanames): Initialize FREE_SSANAMES_QUEUE.
	(fini_ssanames): Finalize FREE_SSANAMES_QUEUE.
	(flush_ssanames_freelist): New function.
	(release_ssaname_fn): Put released names on the queue.
	(pass_release_ssa_names::execute): Call flush_ssanames_freelist.
	* tree-ssanames.h (flush_ssanames_freelist): Declare.

From-SVN: r228302

gcc/ChangeLog

+2015-09-30  Bernd Schmidt  <bernds@redhat.com>
+
+	* gimple-ssa.h (gimple_df): Add free_ssanames_queue field.
+	* passes.c: Include tree-ssanames.h.
+	(execute_function_todo): Flush the pending free SSA_NAMEs after
+	eliminating unreachable basic blocks.
+	* tree-ssanames.c (FREE_SSANAMES_QUEUE): new.
+	(init_ssanames): Initialize FREE_SSANAMES_QUEUE.
+	(fini_ssanames): Finalize FREE_SSANAMES_QUEUE.
+	(flush_ssanames_freelist): New function.
+	(release_ssaname_fn): Put released names on the queue.
+	(pass_release_ssa_names::execute): Call flush_ssanames_freelist.
+	* tree-ssanames.h (flush_ssanames_freelist): Declare.
+
 2015-09-30  Thomas Schwinge  <thomas@codesourcery.com>
 
 	* config/i386/intelmic-mkoffload.c (main): Parse "-v" flag.

gcc/gimple-ssa.h

@@ -90,6 +90,9 @@ struct GTY(()) gimple_df {
   /* Free list of SSA_NAMEs.  */
   vec<tree, va_gc> *free_ssanames;
 
+  /* Queue of SSA_NAMEs to be freed at the next opportunity.  */
+  vec<tree, va_gc> *free_ssanames_queue;
+
   /* Hashtable holding definition for symbol.  If this field is not NULL, it
      means that the first reference to this variable in the function is a
      USE or a VUSE.  In those cases, the SSA renamer creates an SSA name

gcc/passes.c

@@ -84,6 +84,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "cfgrtl.h"
 #include "tree-ssa-live.h"  /* For remove_unused_locals.  */
 #include "tree-cfgcleanup.h"
+#include "tree-ssanames.h"
 
 using namespace gcc;
 
@@ -1913,6 +1914,14 @@ execute_function_todo (function *fn, void *data)
     {
       cleanup_tree_cfg ();
 
+      /* Once unreachable nodes have been removed from the CFG,
+	 there can't be any lingering references to released
+	 SSA_NAMES (because there is no more unreachable code).
+
+	 Thus, now is the time to flush the SSA_NAMEs freelist.  */
+      if (fn->gimple_df)
+	flush_ssaname_freelist ();
+
       /* When cleanup_tree_cfg merges consecutive blocks, it may
 	 perform some simplistic propagation when removing single
 	 valued PHI nodes.  This propagation may, in turn, cause the

gcc/tree-ssanames.c

@@ -70,6 +70,7 @@ unsigned int ssa_name_nodes_reused;
 unsigned int ssa_name_nodes_created;
 
 #define FREE_SSANAMES(fun) (fun)->gimple_df->free_ssanames
+#define FREE_SSANAMES_QUEUE(fun) (fun)->gimple_df->free_ssanames_queue
 
 
 /* Initialize management of SSA_NAMEs to default SIZE.  If SIZE is
@@ -92,6 +93,7 @@ init_ssanames (struct function *fn, int size)
      least 50 elements reserved in it.  */
   SSANAMES (fn)->quick_push (NULL_TREE);
   FREE_SSANAMES (fn) = NULL;
+  FREE_SSANAMES_QUEUE (fn) = NULL;
 
   fn->gimple_df->ssa_renaming_needed = 0;
   fn->gimple_df->rename_vops = 0;
@@ -104,6 +106,7 @@ fini_ssanames (void)
 {
   vec_free (SSANAMES (cfun));
   vec_free (FREE_SSANAMES (cfun));
+  vec_free (FREE_SSANAMES_QUEUE (cfun));
 }
 
 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
@@ -115,6 +118,22 @@ ssanames_print_statistics (void)
   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 }
 
+/* Move all SSA_NAMEs from FREE_SSA_NAMES_QUEUE to FREE_SSA_NAMES.
+
+   We do not, but should have a mode to verify the state of the SSA_NAMEs
+   lists.  In particular at this point every name must be in the IL,
+   on the free list or in the queue.  Anything else is an error.  */
+
+void
+flush_ssaname_freelist (void)
+{
+  while (!vec_safe_is_empty (FREE_SSANAMES_QUEUE (cfun)))
+    {
+      tree t = FREE_SSANAMES_QUEUE (cfun)->pop ();
+      vec_safe_push (FREE_SSANAMES (cfun), t);
+    }
+}
+
 /* Return an SSA_NAME node for variable VAR defined in statement STMT
    in function FN.  STMT may be an empty statement for artificial
    references (e.g., default definitions created when a variable is
@@ -349,8 +368,8 @@ release_ssa_name_fn (struct function *fn, tree var)
       /* Note this SSA_NAME is now in the first list.  */
       SSA_NAME_IN_FREE_LIST (var) = 1;
 
-      /* And finally put it on the free list.  */
-      vec_safe_push (FREE_SSANAMES (fn), var);
+      /* And finally queue it so that it will be put on the free list.  */
+      vec_safe_push (FREE_SSANAMES_QUEUE (fn), var);
     }
 }
 
@@ -631,6 +650,7 @@ unsigned int
 pass_release_ssa_names::execute (function *fun)
 {
   unsigned i, j;
+  flush_ssaname_freelist ();
   int n = vec_safe_length (FREE_SSANAMES (fun));
 
   /* Now release the freelist.  */

gcc/tree-ssanames.h

@@ -98,6 +98,7 @@ extern void reset_flow_sensitive_info (tree);
 extern void reset_flow_sensitive_info_in_bb (basic_block);
 extern void release_defs (gimple *);
 extern void replace_ssa_name_symbol (tree, tree);
+extern void flush_ssaname_freelist (void);
 
 
 /* Return an SSA_NAME node for variable VAR defined in statement STMT