This patch implements A12-0216, which clarifies RM 6.4.1 (6.16-17/3)
concerning illegal overlappings between actuals in a call. The previous
illegality rule applied to a call in which two writable actuals, one
of them having an elementary type, are known to overlap. The new rule
states that illegality only occurs when both actuals are elementary
types (i.e. are identical) because of the non-deterministic order in
which the actuals are rewritten upon return. Other overlaps are not
illegal, but GNAT does emit a warning on them if proper warnings
are enabled.
Tested on x86_64-pc-linux-gnu, committed on trunk
2020-06-16 Ed Schonberg <schonb...@adacore.com>
gcc/ada/
* sem_warn.adb (Warn_On_Overlapping_Actuals): Simplify code and
implement AI12-0216 which clarifies the conditions under which
overlapping actuals in a call are illegal. If proper warnings
are enabled, GNAT also emits warnings in legal cases of
overlopping actuals.--- gcc/ada/sem_warn.adb
+++ gcc/ada/sem_warn.adb
@@ -3674,9 +3674,6 @@ package body Sem_Warn is
Act2 : Node_Id;
Form1 : Entity_Id;
Form2 : Entity_Id;
- Warn_Only : Boolean;
- -- GNAT warns on overlapping in-out parameters of any type, not just for
- -- elementary in-out parameters (as specified in RM 6.4.1 (15/3-17/3)).
-- Start of processing for Warn_On_Overlapping_Actuals
@@ -3686,29 +3683,6 @@ package body Sem_Warn is
return;
end if;
- -- The call is illegal only if there are at least two in-out parameters
- -- of the same elementary type.
-
- Warn_Only := True;
- Form1 := First_Formal (Subp);
- Set_Warn_Only : while Present (Form1) loop
- Form2 := Next_Formal (Form1);
- while Present (Form2) loop
- if Is_Elementary_Type (Etype (Form1))
- and then Is_Elementary_Type (Etype (Form2))
- and then Ekind (Form1) /= E_In_Parameter
- and then Ekind (Form2) /= E_In_Parameter
- then
- Warn_Only := False;
- exit Set_Warn_Only;
- end if;
-
- Next_Formal (Form2);
- end loop;
-
- Next_Formal (Form1);
- end loop Set_Warn_Only;
-
-- Exclude calls rewritten as enumeration literals
if Nkind (N) not in N_Subprogram_Call
@@ -3722,9 +3696,16 @@ package body Sem_Warn is
-- N that is passed as a parameter of mode in out or out to the call C,
-- there is no other name among the other parameters of mode in out or
-- out to C that is known to denote the same object (RM 6.4.1(6.15/3))
+ -- This has been clarified in AI12-0216 to indicate that the illegality
+ -- only occurs if both formals are of an elementary type, bevause of the
+ -- non-determinism on the write-back of the corresponding actuals.
+ -- Earlier versions of the language made it illegal if only one of the
+ -- actuals was an elementary parameter that overlapped a composite
+ -- actual, and both were writable.
-- If appropriate warning switch is set, we also report warnings on
- -- overlapping parameters that are record types or array types.
+ -- overlapping parameters that are composite types. Users find these
+ -- warnings useful, and they used in style guides.
-- It is also worthwhile to warn on overlaps of composite objects when
-- only one of the formals is (in)-out. Note that the RM rule above is
@@ -3836,14 +3817,16 @@ package body Sem_Warn is
-- Overlap is only illegal in Ada 2012 in the case
-- of elementary types (passed by copy). For other
-- types we always have a warning in all versions.
+ -- This is clarified by AI12-0216.
- or else not Is_Elementary_Type (Etype (Form1))
+ or else not
+ (Is_Elementary_Type (Etype (Form1))
+ and then Is_Elementary_Type (Etype (Form2)))
-- debug flag -gnatd.E changes the error to a
-- warning even in Ada 2012 mode.
- or else Error_To_Warning
- or else Warn_Only;
+ or else Error_To_Warning;
if Is_Elementary_Type (Etype (Act1))
and then Ekind (Form2) = E_In_Parameter
