On Sat, Sep 30, 2023 at 11:44:59AM +0200, Jakub Jelinek wrote:
> I really can't figure out why one would need to add extra casts.
> type must be an integral type which has BIT_NOT_EXPR applied on it
> which yields all ones and we need a type in which negating 0 or 1
> range will yield 0 or all ones, I think all integral types satisfy
> that.
> This fixes PR111369, where one of the bitint*.c tests FAILs with
> GCC_TEST_RUN_EXPENSIVE=1.
Though, I think there is an preexisting issue which the
build_nonstandard_integer_type didn't help with; if type is signed 1-bit
precision, then I think a ? ~t : t could be valid, but -(type)a would invoke
UB if a is 1 - the cast would make it -1 and negation of -1 in signed 1-bit
invokes UB.
So perhaps we should guard this optimization on type having element precision >
1
or being unsigned. Plus the (convert:type @2) didn't make sense, @2 already
must have TREE_TYPE type.
So untested patch would be then:
2023-09-29 Jakub Jelinek <ja...@redhat.com>
PR middle-end/111369
* match.pd (a?~t:t -> (-(a))^t): Always convert to type rather
than using build_nonstandard_integer_type. Punt if type is
signed 1-bit precision type.
--- gcc/match.pd.jj 2023-09-29 18:58:42.724956659 +0200
+++ gcc/match.pd 2023-09-30 11:54:16.603280666 +0200
@@ -6741,13 +6741,9 @@ (define_operator_list SYNC_FETCH_AND_AND
(with { bool wascmp; }
(if (INTEGRAL_TYPE_P (type)
&& bitwise_inverted_equal_p (@1, @2, wascmp)
- && (!wascmp || element_precision (type) == 1))
- (with {
- auto prec = TYPE_PRECISION (type);
- auto unsign = TYPE_UNSIGNED (type);
- tree inttype = build_nonstandard_integer_type (prec, unsign);
- }
- (convert (bit_xor (negate (convert:inttype @0)) (convert:inttype @2)))))))
+ && (!wascmp || element_precision (type) == 1)
+ && (!TYPE_OVERFLOW_WRAPS (type) || element_precision (type) > 1))
+ (bit_xor (negate (convert:type @0)) @2))))
#endif
/* Simplify pointer equality compares using PTA. */
Jakub
