All previous versions of GNAT have set overflow checking off by
default (with -gnato switches to enable overflow checking). This
update sets the default to checking on, and implements a new
switch -gnato0 to turn overflow checking on. The old switch
-gnato, which used to enable overflow checking can still be
used but simply sets the default, so normally has no effect.
The following program:
1. procedure OvTest is
2. A : Integer;
3. function Ident (X : Integer) return Integer is
4. begin
5. return X;
6. end;
7. begin
8. A := Ident (Integer'Last) + 1;
9. end;
raises an exception:
raised CONSTRAINT_ERROR : ovtest.adb:8 overflow check failed
if compiled with no options or with -gnato, and runs silently
if compiled with -gnato0.
Tested on x86_64-pc-linux-gnu, committed on trunk
2014-07-31 Robert Dewar <de...@adacore.com>
* gnat1drv.adb (Adjust_Global_Switches): Default for overflow
checking is enabled except in GNAT_Mode.
* switch-c.adb (Scan_Front_End_Switches): Implement -gnato0
(suppress overflow checks).
Index: switch-c.adb
===================================================================
--- switch-c.adb (revision 213263)
+++ switch-c.adb (working copy)
@@ -953,38 +953,57 @@
when 'o' =>
Ptr := Ptr + 1;
- Suppress_Options.Suppress (Overflow_Check) := False;
- -- Case of no digits after the -gnato
+ -- Case of -gnato0 (overflow checking turned off)
- if Ptr > Max or else Switch_Chars (Ptr) not in '1' .. '3' then
+ if Ptr <= Max and then Switch_Chars (Ptr) = '0' then
+ Ptr := Ptr + 1;
+ Suppress_Options.Suppress (Overflow_Check) := True;
+
+ -- We set strict mode in case overflow checking is turned
+ -- on locally (also records that we had a -gnato switch).
+
Suppress_Options.Overflow_Mode_General := Strict;
Suppress_Options.Overflow_Mode_Assertions := Strict;
- -- At least one digit after the -gnato
+ -- All cases other than -gnato0 (overflow checking turned on)
else
- -- Handle first digit after -gnato
+ Suppress_Options.Suppress (Overflow_Check) := False;
- Suppress_Options.Overflow_Mode_General :=
- Get_Overflow_Mode (Switch_Chars (Ptr));
- Ptr := Ptr + 1;
+ -- Case of no digits after the -gnato
- -- Only one digit after -gnato, set assertions mode to
- -- be the same as general mode.
-
if Ptr > Max
or else Switch_Chars (Ptr) not in '1' .. '3'
then
- Suppress_Options.Overflow_Mode_Assertions :=
- Suppress_Options.Overflow_Mode_General;
+ Suppress_Options.Overflow_Mode_General := Strict;
+ Suppress_Options.Overflow_Mode_Assertions := Strict;
- -- Process second digit after -gnato
+ -- At least one digit after the -gnato
else
- Suppress_Options.Overflow_Mode_Assertions :=
+ -- Handle first digit after -gnato
+
+ Suppress_Options.Overflow_Mode_General :=
Get_Overflow_Mode (Switch_Chars (Ptr));
Ptr := Ptr + 1;
+
+ -- Only one digit after -gnato, set assertions mode to be
+ -- the same as general mode.
+
+ if Ptr > Max
+ or else Switch_Chars (Ptr) not in '1' .. '3'
+ then
+ Suppress_Options.Overflow_Mode_Assertions :=
+ Suppress_Options.Overflow_Mode_General;
+
+ -- Process second digit after -gnato
+
+ else
+ Suppress_Options.Overflow_Mode_Assertions :=
+ Get_Overflow_Mode (Switch_Chars (Ptr));
+ Ptr := Ptr + 1;
+ end if;
end if;
end if;
@@ -1026,6 +1045,13 @@
Validity_Checks_On := False;
Opt.Suppress_Checks := True;
+
+ -- Set overflow mode checking to strict in case it gets
+ -- turned on locally (also signals that overflow checking
+ -- has been specifically turned off).
+
+ Suppress_Options.Overflow_Mode_General := Strict;
+ Suppress_Options.Overflow_Mode_Assertions := Strict;
end if;
-- -gnatP (periodic poll)
Index: gnat1drv.adb
===================================================================
--- gnat1drv.adb (revision 213263)
+++ gnat1drv.adb (working copy)
@@ -511,9 +511,13 @@
-- Otherwise set overflow mode defaults
else
- -- Otherwise set overflow checks off by default
+ -- Overflow checks are on by default (Suppress set False) except in
+ -- GNAT_Mode, where we want them off by default (we are not ready to
+ -- enable overflow checks in the compiler yet, for one thing the case
+ -- of 64-bit checks needs System.Arith_64 which is not a compiler
+ -- unit and it is a pain to try to include it in the compiler.
- Suppress_Options.Suppress (Overflow_Check) := True;
+ Suppress_Options.Suppress (Overflow_Check) := GNAT_Mode;
-- Set appropriate default overflow handling mode. Note: at present
-- we set STRICT in all three of the following cases. They are
@@ -531,8 +535,8 @@
-- flags set, so this was dead code anyway.
elsif Targparm.Backend_Divide_Checks_On_Target
- and
- Targparm.Backend_Overflow_Checks_On_Target
+ and
+ Targparm.Backend_Overflow_Checks_On_Target
then
Suppress_Options.Overflow_Mode_General := Strict;
Suppress_Options.Overflow_Mode_Assertions := Strict;
