When overflow checking is enabled, the front end generates range checks
on the indexing of a slice with a bound of the form Boolean'Pos (not X)
that get mistranslated by gigi when optimization is enabled. The checks
should not have been generated in the first place (one is a tautological
full range check and the other redundantly tests that the result of
Boolean'Pos is >= 1), and were only generated because of a missing guard
in Checks.Determine_Range that resulted in a bogus comparison of bounds
against No_Uint.
The following test must compile and execute quietly with -gnato and -O:
$ gnatmake -gnato -O boolean_slice_bound_bug
procedure Boolean_Slice_Bound_Bug is
procedure Proc (B : Boolean) is
S : constant String (1 .. 1) := (others => 'X');
begin
if S (1 .. Boolean'Pos (not B)) /= "X" then
raise Program_Error;
end if;
end Proc;
begin
Proc (False);
end Boolean_Slice_Bound_Bug;
Tested on x86_64-pc-linux-gnu, committed on trunk
2011-09-02 Gary Dismukes <dismu...@adacore.com>
* checks.adb: (Determine_Range): Add test of OK1 to prevent the early
return done when overflow checks are enabled, since comparisons against
Lor and Hir should not be done when OK1 is False.
Index: checks.adb
===================================================================
--- checks.adb (revision 178381)
+++ checks.adb (working copy)
@@ -3479,10 +3479,11 @@
-- to restrict the possible range of results.
-- If one of the computed bounds is outside the range of the base type,
- -- the expression may raise an exception and we better indicate that
+ -- the expression may raise an exception and we had better indicate that
-- the evaluation has failed, at least if checks are enabled.
- if Enable_Overflow_Checks
+ if OK1
+ and then Enable_Overflow_Checks
and then not Is_Entity_Name (N)
and then (Lor < Lo or else Hir > Hi)
then
