From: Jason Merrill <jason@redhat.com>
To: Jakub Jelinek <jakub@redhat.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] c++: Fix up constexpr handling of char/signed char/short pre/post inc/decrement [PR105774]
Date: Mon, 24 Oct 2022 10:07:09 -0400 [thread overview]
Message-ID: <193270d5-60e7-7c03-d88b-5006300768a8@redhat.com> (raw)
In-Reply-To: <Y1Y+XfMW7lkamX2r@tucnak>
On 10/24/22 03:27, Jakub Jelinek wrote:
> Hi!
>
> signed char, char or short int pre/post inc/decrement are represented by
> normal {PRE,POST}_{INC,DEC}REMENT_EXPRs in the FE and only gimplification
> ensures that the {PLUS,MINUS}_EXPR is done in unsigned version of those
> types:
> case PREINCREMENT_EXPR:
> case PREDECREMENT_EXPR:
> case POSTINCREMENT_EXPR:
> case POSTDECREMENT_EXPR:
> {
> tree type = TREE_TYPE (TREE_OPERAND (*expr_p, 0));
> if (INTEGRAL_TYPE_P (type) && c_promoting_integer_type_p (type))
> {
> if (!TYPE_OVERFLOW_WRAPS (type))
> type = unsigned_type_for (type);
> return gimplify_self_mod_expr (expr_p, pre_p, post_p, 1, type);
> }
> break;
> }
> This means during constant evaluation we need to do it similarly (either
> using unsigned_type_for or using widening to integer_type_node).
> The following patch does the latter.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
> 2022-10-24 Jakub Jelinek <jakub@redhat.com>
>
> PR c++/105774
> * constexpr.cc (cxx_eval_increment_expression): For signed types
> that promote to int, evaluate PLUS_EXPR or MINUS_EXPR in int type.
>
> * g++.dg/cpp1y/constexpr-105774.C: New test.
>
> --- gcc/cp/constexpr.cc.jj 2022-10-21 18:04:47.869797312 +0200
> +++ gcc/cp/constexpr.cc 2022-10-23 18:43:27.003390282 +0200
> @@ -6234,6 +6234,18 @@ cxx_eval_increment_expression (const con
> offset = fold_build1 (NEGATE_EXPR, TREE_TYPE (offset), offset);
> mod = fold_build2 (POINTER_PLUS_EXPR, type, val, offset);
> }
> + else if (c_promoting_integer_type_p (type)
> + && !TYPE_UNSIGNED (type)
> + && TYPE_PRECISION (type) < TYPE_PRECISION (integer_type_node))
> + {
> + offset = fold_convert (integer_type_node, offset);
> + mod = fold_convert (integer_type_node, val);
> + tree t = fold_build2 (inc ? PLUS_EXPR : MINUS_EXPR, integer_type_node,
> + mod, offset);
> + mod = fold_convert (type, t);
> + if (TREE_OVERFLOW_P (mod) && !TREE_OVERFLOW_P (t))
> + TREE_OVERFLOW (mod) = false;
> + }
> else
> mod = fold_build2 (inc ? PLUS_EXPR : MINUS_EXPR, type, val, offset);
> if (!ptr)
> --- gcc/testsuite/g++.dg/cpp1y/constexpr-105774.C.jj 2022-10-23 18:44:15.587729613 +0200
> +++ gcc/testsuite/g++.dg/cpp1y/constexpr-105774.C 2022-10-23 18:33:54.754170726 +0200
> @@ -0,0 +1,15 @@
> +// PR c++/105774
> +// { dg-do compile { target c++14 } }
> +
> +constexpr signed char
> +foo ()
> +{
> +#if __SCHAR_MAX__ < __INT_MAX__
> + signed char x = __SCHAR_MAX__;
> +#else
> + signed char x = 0;
> +#endif
> + return ++x;
> +}
> +
> +constexpr auto a = foo ();
>
> Jakub
>
prev parent reply other threads:[~2022-10-24 14:07 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-24 7:27 Jakub Jelinek
2022-10-24 14:07 ` Jason Merrill [this message]
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