[PATCH 2/3] Use sub mode to move block for struct returns

[Jiufu Guo <guojiufu@linux.ibm.com>]

Hi,

This patch checks an assignment to see if it is copy block to a return
variable, and if the function return through registers, then use the
register mode to move sub-blocks for the assignment.

Bootstraped and regtested on ppc{,le} and x86_64.
Is this ok for trunk?

BR,
Jeff (Jiufu)

	PR target/65421

gcc/ChangeLog:

	* cfgexpand.cc (expand_used_vars): Mark DECL_USEDBY_RETURN_P for return
	vars.
	* expr.cc (expand_assignment): Call move_sub_blocks for assining to a
	struct return variable.
	* tree-core.h (struct tree_decl_common): Comment DECL_USEDBY_RETURN_P.
	* tree.h (DECL_USEDBY_RETURN_P): New define.

---
 gcc/cfgexpand.cc | 14 ++++++++++++++
 gcc/expr.cc      | 13 +++++++++++++
 gcc/tree-core.h  |  3 ++-
 gcc/tree.h       |  4 ++++
 4 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc
index dd29ffffc03..0783cb27a59 100644
--- a/gcc/cfgexpand.cc
+++ b/gcc/cfgexpand.cc
@@ -2158,6 +2158,20 @@ expand_used_vars (bitmap forced_stack_vars)
     frame_phase = off ? align - off : 0;
   }
 
+  /* Mark VARs on returns.  */
+  if (DECL_RESULT (current_function_decl))
+    {
+      edge_iterator ei;
+      edge e;
+      FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR_FOR_FN (cfun)->preds)
+	if (greturn *ret = safe_dyn_cast<greturn *> (last_stmt (e->src)))
+	  {
+	    tree val = gimple_return_retval (ret);
+	    if (val && VAR_P (val))
+	      DECL_USEDBY_RETURN_P (val) = 1;
+	  }
+    }
+
   /* Set TREE_USED on all variables in the local_decls.  */
   FOR_EACH_LOCAL_DECL (cfun, i, var)
     TREE_USED (var) = 1;
diff --git a/gcc/expr.cc b/gcc/expr.cc
index 201fee6fd9a..9be75d6733f 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -6115,6 +6115,19 @@ expand_assignment (tree to, tree from, bool nontemporal)
       return;
     }
 
+  /* If it is assigning to a struct var which will be returned, and the
+   function is returning via registers, it would be better to use the
+   register's mode to move sub-blocks for the assignment.  */
+  if (VAR_P (to) && DECL_USEDBY_RETURN_P (to) && mode == BLKmode
+      && TREE_CODE (from) != CONSTRUCTOR
+      && GET_CODE (DECL_RTL (DECL_RESULT (current_function_decl))) == PARALLEL)
+    {
+      rtx ret = DECL_RTL (DECL_RESULT (current_function_decl));
+      machine_mode sub_mode = GET_MODE (XEXP (XVECEXP (ret, 0, 0), 0));
+      move_sub_blocks (to_rtx, from, sub_mode, nontemporal);
+      return;
+    }
+
   /* Compute FROM and store the value in the rtx we got.  */
 
   push_temp_slots ();
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index e146b133dbd..de4acca9ba8 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -1808,7 +1808,8 @@ struct GTY(()) tree_decl_common {
      In VAR_DECL, PARM_DECL and RESULT_DECL, this is
      DECL_HAS_VALUE_EXPR_P.  */
   unsigned decl_flag_2 : 1;
-  /* In FIELD_DECL, this is DECL_PADDING_P.  */
+  /* In FIELD_DECL, this is DECL_PADDING_P
+     In VAR_DECL, this is DECL_USEDBY_RETURN_P.  */
   unsigned decl_flag_3 : 1;
   /* Logically, these two would go in a theoretical base shared by var and
      parm decl. */
diff --git a/gcc/tree.h b/gcc/tree.h
index 4a19de1c94d..b4fbf226ffc 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -3007,6 +3007,10 @@ extern void decl_value_expr_insert (tree, tree);
 #define DECL_PADDING_P(NODE) \
   (FIELD_DECL_CHECK (NODE)->decl_common.decl_flag_3)
 
+/* Used in a VAR_DECL to indicate that it is used by a return stmt.  */
+#define DECL_USEDBY_RETURN_P(NODE) \
+  (VAR_DECL_CHECK (NODE)->decl_common.decl_flag_3)
+
 /* Used in a FIELD_DECL to indicate whether this field is not a flexible
    array member. This is only valid for the last array type field of a
    structure.  */
-- 
2.17.1