[PR 91579] Avoid creating redundant PHI nodes in tail-call pass

2019-08-30  Martin Jambor  <mjambor@suse.cz>

	tree-optimization/91579
	* tree-tailcall.c (tailr_arg_needs_copy): New variable.
	(find_tail_calls): Allocate tailr_arg_needs_copy and set its bits as
	appropriate.
	(arg_needs_copy_p): Removed.
	(eliminate_tail_call): Test tailr_arg_needs_copy instead of calling
	arg_needs_copy_p.
	(tree_optimize_tail_calls_1): Likewise.  Free tailr_arg_needs_copy.

	testsuite/
	* gcc.dg/tree-ssa/pr91579.c: New test.

From-SVN: r275062

1 files changed, 25 insertions, 23 deletions

diff --git a/gcc/tree-tailcall.c b/gcc/tree-tailcall.c
index a4b563e..4824a5e 100644
--- a/gcc/tree-tailcall.c
+++ b/gcc/tree-tailcall.c
@@ -126,6 +126,11 @@ struct tailcall
    accumulator.  */
 static tree m_acc, a_acc;
 
+/* Bitmap with a bit for each function parameter which is set to true if we
+   have to copy the parameter for conversion of tail-recursive calls.  */
+
+static bitmap tailr_arg_needs_copy;
+
 static bool optimize_tail_call (struct tailcall *, bool);
 static void eliminate_tail_call (struct tailcall *);
 
@@ -727,6 +732,18 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
 	  gimple_stmt_iterator mgsi = gsi_for_stmt (stmt);
 	  gsi_move_before (&mgsi, &gsi);
 	}
+      if (!tailr_arg_needs_copy)
+	tailr_arg_needs_copy = BITMAP_ALLOC (NULL);
+      for (param = DECL_ARGUMENTS (current_function_decl), idx = 0;
+	   param;
+	   param = DECL_CHAIN (param), idx++)
+	{
+	  tree ddef, arg = gimple_call_arg (call, idx);
+	  if (is_gimple_reg (param)
+	      && (ddef = ssa_default_def (cfun, param))
+	      && (arg != ddef))
+	    bitmap_set_bit (tailr_arg_needs_copy, idx);
+	}
     }
 
   nw = XNEW (struct tailcall);
@@ -905,25 +922,6 @@ decrease_profile (basic_block bb, profile_count count)
     }
 }
 
-/* Returns true if argument PARAM of the tail recursive call needs to be copied
-   when the call is eliminated.  */
-
-static bool
-arg_needs_copy_p (tree param)
-{
-  tree def;
-
-  if (!is_gimple_reg (param))
-    return false;
-
-  /* Parameters that are only defined but never used need not be copied.  */
-  def = ssa_default_def (cfun, param);
-  if (!def)
-    return false;
-
-  return true;
-}
-
 /* Eliminates tail call described by T.  TMP_VARS is a list of
    temporary variables used to copy the function arguments.  */
 
@@ -1005,7 +1003,7 @@ eliminate_tail_call (struct tailcall *t)
        param;
        param = DECL_CHAIN (param), idx++)
     {
-      if (!arg_needs_copy_p (param))
+      if (!bitmap_bit_p (tailr_arg_needs_copy, idx))
 	continue;
 
       arg = gimple_call_arg (stmt, idx);
@@ -1139,10 +1137,11 @@ tree_optimize_tail_calls_1 (bool opt_tailcalls)
 	      split_edge (single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
 
 	  /* Copy the args if needed.  */
-	  for (param = DECL_ARGUMENTS (current_function_decl);
+	  unsigned idx;
+	  for (param = DECL_ARGUMENTS (current_function_decl), idx = 0;
 	       param;
-	       param = DECL_CHAIN (param))
-	    if (arg_needs_copy_p (param))
+	       param = DECL_CHAIN (param), idx++)
+	    if (bitmap_bit_p (tailr_arg_needs_copy, idx))
 	      {
 		tree name = ssa_default_def (cfun, param);
 		tree new_name = make_ssa_name (param, SSA_NAME_DEF_STMT (name));
@@ -1206,6 +1205,9 @@ tree_optimize_tail_calls_1 (bool opt_tailcalls)
   if (phis_constructed)
     mark_virtual_operands_for_renaming (cfun);
 
+  if (tailr_arg_needs_copy)
+    BITMAP_FREE (tailr_arg_needs_copy);
+
   if (changed)
     return TODO_cleanup_cfg | TODO_update_ssa_only_virtuals;
   return 0;