On Sat, 30 Sep 2023, Jakub Jelinek wrote:
> 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.
Alternatively cast to unsigned:1 in that case? OTOH when element
precision is 1 we can also simply elide the negation?
> 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
>
>
--
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