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[Ada] Fix internal error on extended return and fixed-point result

Message ID 20201130141712.GA117888@adacore.com
State New
Headers show
Series [Ada] Fix internal error on extended return and fixed-point result | expand

Commit Message

Pierre-Marie de Rodat Nov. 30, 2020, 2:17 p.m. UTC 
This prevents the expander from creating an access before elaboration
issue for a temporary generated for a range check applied to the
expression of a degenerate extended return statement (an extended return
statement without an explicit do/end construct).

Expand_N_Extended_Return_Statement has got a fast track for this case,
but it does not do what it is supposed to do and ends up generating both
the declaration of the return object with the expresion and the direct
return of the expression, which is problematic if the direct return is
analyzed again and subject to a range check.

The patch reimplements the fast track as documented and makes sure that
it is used only when the declaration of the return object can be
dropped.  It also contains a fixlet for
Check_Type_Or_Object_External_Properties.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* contracts.adb (Check_Type_Or_Object_External_Properties): Make
	sure to exclude all return objects from the SPARK legality rule
	on effectively volatile variables.
	* exp_ch6.adb (Expand_N_Extended_Return_Statement): Use the fast
	track only when the declaration of the return object can be
	dropped.
diff mbox series

Patch

diff --git a/gcc/ada/contracts.adb b/gcc/ada/contracts.adb
--- a/gcc/ada/contracts.adb
+++ b/gcc/ada/contracts.adb
@@ -905,9 +905,12 @@  package body Contracts is
 
       --  The following checks are relevant only when SPARK_Mode is on, as
       --  they are not standard Ada legality rules. Internally generated
-      --  temporaries are ignored.
+      --  temporaries are ignored, as well as return objects.
 
-      if SPARK_Mode = On and then Comes_From_Source (Type_Or_Obj_Id) then
+      if SPARK_Mode = On
+        and then Comes_From_Source (Type_Or_Obj_Id)
+        and then not Is_Return_Object (Type_Or_Obj_Id)
+      then
          if Is_Effectively_Volatile (Type_Or_Obj_Id) then
 
             --  The declaration of an effectively volatile object or type must


diff --git a/gcc/ada/exp_ch6.adb b/gcc/ada/exp_ch6.adb
--- a/gcc/ada/exp_ch6.adb
+++ b/gcc/ada/exp_ch6.adb
@@ -5384,13 +5384,15 @@  package body Exp_Ch6 is
       end if;
 
       --  Build a simple_return_statement that returns the return object when
-      --  there is a statement sequence, or no expression, or the result will
-      --  be built in place. Note however that we currently do this for all
-      --  composite cases, even though not all are built in place.
+      --  there is a statement sequence, or no expression, or the analysis of
+      --  the return object declaration generated extra actions, or the result
+      --  will be built in place. Note however that we currently do this for
+      --  all composite cases, even though they are not built in place.
 
       if Present (HSS)
-        or else Is_Composite_Type (Ret_Typ)
         or else No (Exp)
+        or else List_Length (Return_Object_Declarations (N)) > 1
+        or else Is_Composite_Type (Ret_Typ)
       then
          if No (HSS) then
             Stmts := New_List;
@@ -6058,16 +6060,11 @@  package body Exp_Ch6 is
             end;
          end if;
 
-      --  Case where we do not build a block
-
-      else
-         --  We're about to drop Return_Object_Declarations on the floor, so
-         --  we need to insert it, in case it got expanded into useful code.
-         --  Remove side effects from expression, which may be duplicated in
-         --  subsequent checks (see Expand_Simple_Function_Return).
+      --  Case where we do not need to build a block. But we're about to drop
+      --  Return_Object_Declarations on the floor, so assert that it contains
+      --  only the return object declaration.
 
-         Insert_List_Before (N, Return_Object_Declarations (N));
-         Remove_Side_Effects (Exp);
+      else pragma Assert (List_Length (Return_Object_Declarations (N)) = 1);
 
          --  Build simple_return_statement that returns the expression directly