Hi,
on the attached testcase, the Ada compiler gives a bogus warning:
storage_offset1.ads:16:52: warning: Constraint_Error will be raised at run
time [enabled by default]
This directly comes from the GENERIC folding setting a bogus TREE_OVERFLOW on
an INTEGER_CST during the (T)P - (T)(P + A) -> -(T) A transformation:
/* (T)P - (T)(P + A) -> -(T) A */
(simplify
(minus (convert? @0)
(convert (plus:c @@0 @1)))
(if (INTEGRAL_TYPE_P (type)
&& TYPE_OVERFLOW_UNDEFINED (type)
&& element_precision (type) <= element_precision (TREE_TYPE (@1)))
(with { tree utype = unsigned_type_for (type); }
(convert (negate (convert:utype @1))))
(if (element_precision (type) <= element_precision (TREE_TYPE (@1))
/* For integer types, if A has a smaller type
than T the result depends on the possible
overflow in P + A.
E.g. T=size_t, A=(unsigned)429497295, P>0.
However, if an overflow in P + A would cause
undefined behavior, we can assume that there
is no overflow. */
|| (INTEGRAL_TYPE_P (TREE_TYPE (@1))
&& TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@1))))
(negate (convert @1)))))
(simplify
(minus (convert @0)
(convert (pointer_plus @@0 @1)))
(if (INTEGRAL_TYPE_P (type)
&& TYPE_OVERFLOW_UNDEFINED (type)
&& element_precision (type) <= element_precision (TREE_TYPE (@1)))
(with { tree utype = unsigned_type_for (type); }
(convert (negate (convert:utype @1))))
(if (element_precision (type) <= element_precision (TREE_TYPE (@1))
/* For pointer types, if the conversion of A to the
final type requires a sign- or zero-extension,
then we have to punt - it is not defined which
one is correct. */
|| (POINTER_TYPE_P (TREE_TYPE (@0))
&& TREE_CODE (@1) == INTEGER_CST
&& tree_int_cst_sign_bit (@1) == 0))
(negate (convert @1)))))
Ironically enough, this occurs because of the intermediate conversion to an
unsigned type which is supposed to hide overflows, but is counter-productive
for constants because TREE_OVERFLOW is always set for them, so it ends up
setting a bogus TREE_OVERFLOW when converting back to the original type.
The fix simply redirects INTEGER_CSTs to the other, direct path without the
intermediate conversion to the unsigned type.
Tested on x86-64/Linux, OK for the mainline?
2023-05-24 Eric Botcazou <ebotca...@adacore.com>
* match.pd ((T)P - (T)(P + A) -> -(T) A): Avoid artificial overflow
on constants.
2023-05-24 Eric Botcazou <ebotca...@adacore.com>
* gnat.dg/specs/storage_offset1.ads: New test.
--
Eric Botcazoudiff --git a/gcc/match.pd b/gcc/match.pd
index 1fe0559acfb..b9d04dd423b 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3194,6 +3194,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(convert (plus:c @@0 @1)))
(if (INTEGRAL_TYPE_P (type)
&& TYPE_OVERFLOW_UNDEFINED (type)
+ && TREE_CODE (@1) != INTEGER_CST
&& element_precision (type) <= element_precision (TREE_TYPE (@1)))
(with { tree utype = unsigned_type_for (type); }
(convert (negate (convert:utype @1))))
@@ -3213,6 +3214,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(convert (pointer_plus @@0 @1)))
(if (INTEGRAL_TYPE_P (type)
&& TYPE_OVERFLOW_UNDEFINED (type)
+ && TREE_CODE (@1) != INTEGER_CST
&& element_precision (type) <= element_precision (TREE_TYPE (@1)))
(with { tree utype = unsigned_type_for (type); }
(convert (negate (convert:utype @1))))
-- { dg-do compile }
with System.Storage_Elements; use System.Storage_Elements;
with System;
package Storage_Offset1 is
type Rec is record
I1, I2 : Integer;
end record;
type Ptr is access all Rec;
R : Ptr := new Rec;
Offset : constant Storage_Offset := R.I1'Address - R.I2'Address;
end Storage_Offset1;
