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* [gcc r13-668] [Ada] Avoid copy operation for returns involving function calls
@ 2022-05-19 14:09 Pierre-Marie de Rodat
0 siblings, 0 replies; only message in thread
From: Pierre-Marie de Rodat @ 2022-05-19 14:09 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:9aa9ba95ea3d4800974135da85fd4d9cd310b69e
commit r13-668-g9aa9ba95ea3d4800974135da85fd4d9cd310b69e
Author: Eric Botcazou <ebotcazou@adacore.com>
Date: Tue Apr 12 23:34:48 2022 +0200
[Ada] Avoid copy operation for returns involving function calls
gcc/ada/
* gcc-interface/decl.cc (gnat_to_gnu_entity) <E_Constant>: Deal with
a constant related to a return in a function specially.
* gcc-interface/trans.cc (Call_to_gnu): Use return slot optimization
if the target is a return object.
(gnat_to_gnu) <N_Object_Declaration>: Deal with a constant related
to a return in a function specially.
Diff:
---
gcc/ada/gcc-interface/decl.cc | 11 +++++++++++
gcc/ada/gcc-interface/trans.cc | 42 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 53 insertions(+)
diff --git a/gcc/ada/gcc-interface/decl.cc b/gcc/ada/gcc-interface/decl.cc
index 2d9b41f984c..50d17f75562 100644
--- a/gcc/ada/gcc-interface/decl.cc
+++ b/gcc/ada/gcc-interface/decl.cc
@@ -630,6 +630,17 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
break;
case E_Constant:
+ /* If this is a constant related to a return in a function returning by
+ invisible reference without expression, get the return object. */
+ if (Is_Related_To_Func_Return (gnat_entity)
+ && current_function_decl
+ && TREE_ADDRESSABLE (TREE_TYPE (current_function_decl))
+ && !gnu_expr)
+ {
+ gnu_decl = DECL_RESULT (current_function_decl);
+ break;
+ }
+
/* Ignore constant definitions already marked with the error node. See
the N_Object_Declaration case of gnat_to_gnu for the rationale. */
if (definition
diff --git a/gcc/ada/gcc-interface/trans.cc b/gcc/ada/gcc-interface/trans.cc
index 3e8842f4a92..e80200ee46a 100644
--- a/gcc/ada/gcc-interface/trans.cc
+++ b/gcc/ada/gcc-interface/trans.cc
@@ -5281,6 +5281,15 @@ Call_to_gnu (Node_Id gnat_node, tree *gnu_result_type_p, tree gnu_target,
&& return_slot_opt_for_pure_call_p (gnu_target, gnu_call))
op_code = INIT_EXPR;
+ /* If this is the initialization of a return object in a function
+ returning by invisible reference, we can always use the return
+ slot optimization. */
+ else if (TREE_CODE (gnu_target) == INDIRECT_REF
+ && TREE_CODE (TREE_OPERAND (gnu_target, 0)) == RESULT_DECL
+ && current_function_decl
+ && TREE_ADDRESSABLE (TREE_TYPE (current_function_decl)))
+ op_code = INIT_EXPR;
+
else
op_code = MODIFY_EXPR;
@@ -6380,6 +6389,39 @@ gnat_to_gnu (Node_Id gnat_node)
|| Is_Concurrent_Type (Etype (gnat_temp))))
break;
+ /* If this is a constant related to a return initialized by a reference
+ to a function call in a function returning by invisible reference:
+
+ type Ann is access all Result_Type;
+ Rnn : constant Ann := Func'reference;
+ [...]
+ return Rnn.all;
+
+ then elide the temporary by forwarding the return object to Func:
+
+ *<retval> = Func (); [return slot optimization]
+ [...]
+ return <retval>;
+
+ That's necessary if the result type needs finalization because the
+ temporary would never be adjusted as Expand_Simple_Function_Return
+ also elides the temporary in this case. */
+ if (Ekind (gnat_temp) == E_Constant
+ && Is_Related_To_Func_Return (gnat_temp)
+ && Nkind (Expression (gnat_node)) == N_Reference
+ && Nkind (Prefix (Expression (gnat_node))) == N_Function_Call
+ && current_function_decl
+ && TREE_ADDRESSABLE (TREE_TYPE (current_function_decl)))
+ {
+ gnu_result = gnat_to_gnu_entity (gnat_temp, NULL_TREE, true);
+ gnu_result = build_unary_op (INDIRECT_REF, NULL_TREE, gnu_result);
+ gnu_result
+ = Call_to_gnu (Prefix (Expression (gnat_node)),
+ &gnu_result_type, gnu_result,
+ NOT_ATOMIC, false);
+ break;
+ }
+
if (Present (Expression (gnat_node))
&& !(kind == N_Object_Declaration && No_Initialization (gnat_node))
&& (!type_annotate_only
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