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Don't inherit range-type signed-ness from underlying type

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A recent commit changed gdb to inherit the signed-ness of a range type
from its underlying type:

    commit cfabbd351a174406fd5aa063303f5c8bf9266bbc
    Author: Tom Tromey <tom@tromey.com>
    Date:   Sat Oct 17 11:41:59 2020 -0600

      Make range types inherit signed-ness from base type

This passed testing -- but unfortunately, additional testing at
AdaCore showed that this change was incorrect.  GNAT, at least, can
emit an unsigned range type whose underlying type is signed.

This patch reverts the code change from the above.  I chose not to
reintroduce the FIXME comments, because now we know that they are
incorrect.  Instead, this patch also adds a comment to
create_range_type.

A new test case is included as well.

2020-10-26  Tom Tromey  <tromey@adacore.com>

	* gdbtypes.c (create_range_type): Revert previous patch.  Add
	comment.

gdb/testsuite/ChangeLog
2020-10-26  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/unsigned_range/foo.adb: New file.
	* gdb.ada/unsigned_range/pack.adb: New file.
	* gdb.ada/unsigned_range/pack.ads: New file.
	* gdb.ada/unsigned_range.exp: New file.
This commit is contained in:
Tom Tromey
2020-10-26 12:54:19 -06:00
parent d744f0f965
commit 6390859caa
7 changed files with 141 additions and 1 deletions
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17
gdb/gdbtypes.c
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@ -950,7 +950,22 @@ create_range_type (struct type *result_type, struct type *index_type,
result_type->set_bounds (bounds);
result_type->set_is_unsigned (index_type->is_unsigned ());
/* Note that the signed-ness of a range type can't simply be copied
from the underlying type. Consider a case where the underlying
type is 'int', but the range type can hold 0..65535, and where
the range is further specified to fit into 16 bits. In this
case, if we copy the underlying type's sign, then reading some
range values will cause an unwanted sign extension. So, we have
some heuristics here instead. */
if (low_bound->kind () == PROP_CONST && low_bound->const_val () >= 0)
result_type->set_is_unsigned (true);
/* Ada allows the declaration of range types whose upper bound is
less than the lower bound, so checking the lower bound is not
enough. Make sure we do not mark a range type whose upper bound
is negative as unsigned. */
if (high_bound->kind () == PROP_CONST && high_bound->const_val () < 0)
result_type->set_is_unsigned (false);
result_type->set_endianity_is_not_default
(index_type->endianity_is_not_default ());