From: Jason Merrill <jason@redhat.com>
To: Patrick Palka <ppalka@redhat.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH 2/2] c++: speculative constexpr and is_constant_evaluated [PR108243]
Date: Sun, 5 Feb 2023 12:11:28 -0800 [thread overview]
Message-ID: <1ba53fb8-f688-b680-75f9-a158fa0d679b@redhat.com> (raw)
In-Reply-To: <8ca008ee-d56c-52d9-4f3f-3f738e0e8af6@idea>
On 2/3/23 15:51, Patrick Palka wrote:
> On Mon, 30 Jan 2023, Jason Merrill wrote:
>
>> On 1/27/23 17:02, Patrick Palka wrote:
>>> This PR illustrates that __builtin_is_constant_evaluated currently acts
>>> as an optimization barrier for our speculative constexpr evaluation,
>>> since we don't want to prematurely fold the builtin to false if the
>>> expression in question would be later manifestly constant evaluated (in
>>> which case it must be folded to true).
>>>
>>> This patch fixes this by permitting __builtin_is_constant_evaluated
>>> to get folded as false during cp_fold_function, since at that point
>>> we're sure we're doing manifestly constant evaluation. To that end
>>> we add a flags parameter to cp_fold that controls what mce_value the
>>> CALL_EXPR case passes to maybe_constant_value.
>>>
>>> bootstrapped and rgetsted no x86_64-pc-linux-gnu, does this look OK for
>>> trunk?
>>>
>>> PR c++/108243
>>>
>>> gcc/cp/ChangeLog:
>>>
>>> * cp-gimplify.cc (enum fold_flags): Define.
>>> (cp_fold_data::genericize): Replace this data member with ...
>>> (cp_fold_data::fold_flags): ... this.
>>> (cp_fold_r): Adjust cp_fold_data use and cp_fold_calls.
>>> (cp_fold_function): Likewise.
>>> (cp_fold_maybe_rvalue): Likewise.
>>> (cp_fully_fold_init): Likewise.
>>> (cp_fold): Add fold_flags parameter. Don't cache if flags
>>> isn't empty.
>>> <case CALL_EXPR>: Pass mce_false to maybe_constant_value
>>> if if ff_genericize is set.
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>> * g++.dg/opt/pr108243.C: New test.
>>> ---
>>> gcc/cp/cp-gimplify.cc | 76 ++++++++++++++++++-----------
>>> gcc/testsuite/g++.dg/opt/pr108243.C | 29 +++++++++++
>>> 2 files changed, 76 insertions(+), 29 deletions(-)
>>> create mode 100644 gcc/testsuite/g++.dg/opt/pr108243.C
>>>
>>> diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
>>> index a35cedd05cc..d023a63768f 100644
>>> --- a/gcc/cp/cp-gimplify.cc
>>> +++ b/gcc/cp/cp-gimplify.cc
>>> @@ -43,12 +43,20 @@ along with GCC; see the file COPYING3. If not see
>>> #include "omp-general.h"
>>> #include "opts.h"
>>> +/* Flags for cp_fold and cp_fold_r. */
>>> +
>>> +enum fold_flags {
>>> + ff_none = 0,
>>> + /* Whether we're being called from cp_fold_function. */
>>> + ff_genericize = 1 << 0,
>>> +};
>>> +
>>> /* Forward declarations. */
>>> static tree cp_genericize_r (tree *, int *, void *);
>>> static tree cp_fold_r (tree *, int *, void *);
>>> static void cp_genericize_tree (tree*, bool);
>>> -static tree cp_fold (tree);
>>> +static tree cp_fold (tree, fold_flags);
>>> /* Genericize a TRY_BLOCK. */
>>> @@ -996,9 +1004,8 @@ struct cp_genericize_data
>>> struct cp_fold_data
>>> {
>>> hash_set<tree> pset;
>>> - bool genericize; // called from cp_fold_function?
>>> -
>>> - cp_fold_data (bool g): genericize (g) {}
>>> + fold_flags flags;
>>> + cp_fold_data (fold_flags flags): flags (flags) {}
>>> };
>>> static tree
>>> @@ -1039,7 +1046,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void
>>> *data_)
>>> break;
>>> }
>>> - *stmt_p = stmt = cp_fold (*stmt_p);
>>> + *stmt_p = stmt = cp_fold (*stmt_p, data->flags);
>>> if (data->pset.add (stmt))
>>> {
>>> @@ -1119,12 +1126,12 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void
>>> *data_)
>>> here rather than in cp_genericize to avoid problems with the
>>> invisible
>>> reference transition. */
>>> case INIT_EXPR:
>>> - if (data->genericize)
>>> + if (data->flags & ff_genericize)
>>> cp_genericize_init_expr (stmt_p);
>>> break;
>>> case TARGET_EXPR:
>>> - if (data->genericize)
>>> + if (data->flags & ff_genericize)
>>> cp_genericize_target_expr (stmt_p);
>>> /* Folding might replace e.g. a COND_EXPR with a TARGET_EXPR; in
>>> @@ -1157,7 +1164,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void
>>> *data_)
>>> void
>>> cp_fold_function (tree fndecl)
>>> {
>>> - cp_fold_data data (/*genericize*/true);
>>> + cp_fold_data data (ff_genericize);
>>> cp_walk_tree (&DECL_SAVED_TREE (fndecl), cp_fold_r, &data, NULL);
>>> }
>>> @@ -2375,7 +2382,7 @@ cp_fold_maybe_rvalue (tree x, bool rval)
>>> {
>>> while (true)
>>> {
>>> - x = cp_fold (x);
>>> + x = cp_fold (x, ff_none);
>>> if (rval)
>>> x = mark_rvalue_use (x);
>>> if (rval && DECL_P (x)
>>> @@ -2434,7 +2441,7 @@ cp_fully_fold_init (tree x)
>>> if (processing_template_decl)
>>> return x;
>>> x = cp_fully_fold (x);
>>> - cp_fold_data data (/*genericize*/false);
>>> + cp_fold_data data (ff_none);
>>> cp_walk_tree (&x, cp_fold_r, &data, NULL);
>>> return x;
>>> }
>>> @@ -2469,7 +2476,7 @@ clear_fold_cache (void)
>>> Function returns X or its folded variant. */
>>> static tree
>>> -cp_fold (tree x)
>>> +cp_fold (tree x, fold_flags flags)
>>> {
>>> tree op0, op1, op2, op3;
>>> tree org_x = x, r = NULL_TREE;
>>> @@ -2490,8 +2497,11 @@ cp_fold (tree x)
>>> if (fold_cache == NULL)
>>> fold_cache = hash_map<tree, tree>::create_ggc (101);
>>> - if (tree *cached = fold_cache->get (x))
>>> - return *cached;
>>> + bool cache_p = (flags == ff_none);
>>> +
>>> + if (cache_p)
>>> + if (tree *cached = fold_cache->get (x))
>>> + return *cached;
>>> uid_sensitive_constexpr_evaluation_checker c;
>>> @@ -2526,7 +2536,7 @@ cp_fold (tree x)
>>> Don't create a new tree if op0 != TREE_OPERAND (x, 0), the
>>> folding of the operand should be in the caches and if in
>>> cp_fold_r
>>> it will modify it in place. */
>>> - op0 = cp_fold (TREE_OPERAND (x, 0));
>>> + op0 = cp_fold (TREE_OPERAND (x, 0), flags);
>>> if (op0 == error_mark_node)
>>> x = error_mark_node;
>>> break;
>>> @@ -2571,7 +2581,7 @@ cp_fold (tree x)
>>> {
>>> tree p = maybe_undo_parenthesized_ref (x);
>>> if (p != x)
>>> - return cp_fold (p);
>>> + return cp_fold (p, flags);
>>> }
>>> goto unary;
>>> @@ -2763,8 +2773,8 @@ cp_fold (tree x)
>>> case COND_EXPR:
>>> loc = EXPR_LOCATION (x);
>>> op0 = cp_fold_rvalue (TREE_OPERAND (x, 0));
>>> - op1 = cp_fold (TREE_OPERAND (x, 1));
>>> - op2 = cp_fold (TREE_OPERAND (x, 2));
>>> + op1 = cp_fold (TREE_OPERAND (x, 1), flags);
>>> + op2 = cp_fold (TREE_OPERAND (x, 2), flags);
>>> if (TREE_CODE (TREE_TYPE (x)) == BOOLEAN_TYPE)
>>> {
>>> @@ -2854,7 +2864,7 @@ cp_fold (tree x)
>>> {
>>> if (!same_type_p (TREE_TYPE (x), TREE_TYPE (r)))
>>> r = build_nop (TREE_TYPE (x), r);
>>> - x = cp_fold (r);
>>> + x = cp_fold (r, flags);
>>> break;
>>> }
>>> }
>>> @@ -2908,7 +2918,7 @@ cp_fold (tree x)
>>> int m = call_expr_nargs (x);
>>> for (int i = 0; i < m; i++)
>>> {
>>> - r = cp_fold (CALL_EXPR_ARG (x, i));
>>> + r = cp_fold (CALL_EXPR_ARG (x, i), flags);
>>> if (r != CALL_EXPR_ARG (x, i))
>>> {
>>> if (r == error_mark_node)
>>> @@ -2931,7 +2941,7 @@ cp_fold (tree x)
>>> if (TREE_CODE (r) != CALL_EXPR)
>>> {
>>> - x = cp_fold (r);
>>> + x = cp_fold (r, flags);
>>> break;
>>> }
>>> @@ -2944,7 +2954,15 @@ cp_fold (tree x)
>>> constant, but the call followed by an INDIRECT_REF is. */
>>> if (callee && DECL_DECLARED_CONSTEXPR_P (callee)
>>> && !flag_no_inline)
>>> - r = maybe_constant_value (x);
>>> + {
>>> + mce_value manifestly_const_eval = mce_unknown;
>>> + if (flags & ff_genericize)
>>> + /* At genericization time it's safe to fold
>>> + __builtin_is_constant_evaluated to false. */
>>> + manifestly_const_eval = mce_false;
>>> + r = maybe_constant_value (x, /*decl=*/NULL_TREE,
>>> + manifestly_const_eval);
>>> + }
>>> optimize = sv;
>>> if (TREE_CODE (r) != CALL_EXPR)
>>> @@ -2971,7 +2989,7 @@ cp_fold (tree x)
>>> vec<constructor_elt, va_gc> *nelts = NULL;
>>> FOR_EACH_VEC_SAFE_ELT (elts, i, p)
>>> {
>>> - tree op = cp_fold (p->value);
>>> + tree op = cp_fold (p->value, flags);
>>> if (op != p->value)
>>> {
>>> if (op == error_mark_node)
>>> @@ -3002,7 +3020,7 @@ cp_fold (tree x)
>>> for (int i = 0; i < n; i++)
>>> {
>>> - tree op = cp_fold (TREE_VEC_ELT (x, i));
>>> + tree op = cp_fold (TREE_VEC_ELT (x, i), flags);
>>> if (op != TREE_VEC_ELT (x, i))
>>> {
>>> if (!changed)
>>> @@ -3019,10 +3037,10 @@ cp_fold (tree x)
>>> case ARRAY_RANGE_REF:
>>> loc = EXPR_LOCATION (x);
>>> - op0 = cp_fold (TREE_OPERAND (x, 0));
>>> - op1 = cp_fold (TREE_OPERAND (x, 1));
>>> - op2 = cp_fold (TREE_OPERAND (x, 2));
>>> - op3 = cp_fold (TREE_OPERAND (x, 3));
>>> + op0 = cp_fold (TREE_OPERAND (x, 0), flags);
>>> + op1 = cp_fold (TREE_OPERAND (x, 1), flags);
>>> + op2 = cp_fold (TREE_OPERAND (x, 2), flags);
>>> + op3 = cp_fold (TREE_OPERAND (x, 3), flags);
>>> if (op0 != TREE_OPERAND (x, 0)
>>> || op1 != TREE_OPERAND (x, 1)
>>> @@ -3050,7 +3068,7 @@ cp_fold (tree x)
>>> /* A SAVE_EXPR might contain e.g. (0 * i) + (0 * j), which, after
>>> folding, evaluates to an invariant. In that case no need to wrap
>>> this folded tree with a SAVE_EXPR. */
>>> - r = cp_fold (TREE_OPERAND (x, 0));
>>> + r = cp_fold (TREE_OPERAND (x, 0), flags);
>>> if (tree_invariant_p (r))
>>> x = r;
>>> break;
>>> @@ -3069,7 +3087,7 @@ cp_fold (tree x)
>>> copy_warning (x, org_x);
>>> }
>>> - if (!c.evaluation_restricted_p ())
>>> + if (cache_p && !c.evaluation_restricted_p ())
>>> {
>>> fold_cache->put (org_x, x);
>>> /* Prevent that we try to fold an already folded result again. */
>>> diff --git a/gcc/testsuite/g++.dg/opt/pr108243.C
>>> b/gcc/testsuite/g++.dg/opt/pr108243.C
>>> new file mode 100644
>>> index 00000000000..4c45dbba13c
>>> --- /dev/null
>>> +++ b/gcc/testsuite/g++.dg/opt/pr108243.C
>>> @@ -0,0 +1,29 @@
>>> +// PR c++/108243
>>> +// { dg-do compile { target c++11 } }
>>> +// { dg-additional-options "-O -fdump-tree-original" }
>>> +
>>> +constexpr int foo() {
>>> + return __builtin_is_constant_evaluated() + 1;
>>> +}
>>> +
>>> +#if __cpp_if_consteval
>>> +constexpr int bar() {
>>> + if consteval {
>>> + return 5;
>>> + } else {
>>> + return 4;
>>> + }
>>> +}
>>> +#endif
>>> +
>>> +int p, q;
>>> +
>>> +int main() {
>>> + p = foo();
>>> +#if __cpp_if_consteval
>>> + q = bar();
>>> +#endif
>>> +}
>>> +
>>> +// { dg-final { scan-tree-dump-not "= foo" "original" } }
>>> +// { dg-final { scan-tree-dump-not "= bar" "original" } }
>>
>> Let's also test a static initializer that can't be fully constant-evaluated.
>
> D'oh, doing so revealed that cp_fold_function doesn't reach static
> initializers; that's taken care of by cp_fully_fold_init. So it seems
> we need to make cp_fold when called from the latter entry point to also
> assume m_c_e is false. We can't re-use ff_genericize here because that
> flag has additional effects in cp_fold_r, so it seems we need another
> flag that that only affects the manifestly constant-eval stuff; I called
> it ff_mce_false. How does the following look?
>
> -- >8 --
>
> Subject: [PATCH 2/2] c++: speculative constexpr and is_constant_evaluated
> [PR108243]
>
> This PR illustrates that __builtin_is_constant_evaluated currently acts
> as an optimization barrier for our speculative constexpr evaluation,
> since we don't want to prematurely fold the builtin to false if the
> expression in question would be later manifestly constant evaluated (in
> which case it must be folded to true).
>
> This patch fixes this by permitting __builtin_is_constant_evaluated
> to get folded as false during cp_fold_function and cp_fully_fold_init,
> since at these points we're sure we're done with manifestly constant
> evaluation. To that end we add a flags parameter to cp_fold that
> controls whether we pass mce_false or mce_unknown to maybe_constant_value
> when folding a CALL_EXPR.
>
> PR c++/108243
> PR c++/97553
>
> gcc/cp/ChangeLog:
>
> * cp-gimplify.cc (enum fold_flags): Define.
> (cp_fold_data::genericize): Replace this data member with ...
> (cp_fold_data::fold_flags): ... this.
> (cp_fold_r): Adjust use of cp_fold_data and calls to cp_fold.
> (cp_fold_function): Likewise.
> (cp_fold_maybe_rvalue): Likewise.
> (cp_fully_fold_init): Likewise.
> (cp_fold): Add fold_flags parameter. Don't cache if flags
> isn't empty.
> <case CALL_EXPR>: If ff_genericize is set, fold
> __builtin_is_constant_evaluated to false and pass mce_false to
> maybe_constant_value.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/opt/is_constant_evaluated1.C: New test.
> * g++.dg/opt/is_constant_evaluated2.C: New test.
> ---
> gcc/cp/cp-gimplify.cc | 88 ++++++++++++-------
> .../g++.dg/opt/is_constant_evaluated1.C | 14 +++
> .../g++.dg/opt/is_constant_evaluated2.C | 32 +++++++
> 3 files changed, 104 insertions(+), 30 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/opt/is_constant_evaluated1.C
> create mode 100644 gcc/testsuite/g++.dg/opt/is_constant_evaluated2.C
>
> diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
> index 9929d29981a..590ed787997 100644
> --- a/gcc/cp/cp-gimplify.cc
> +++ b/gcc/cp/cp-gimplify.cc
> @@ -43,12 +43,26 @@ along with GCC; see the file COPYING3. If not see
> #include "omp-general.h"
> #include "opts.h"
>
> +/* Flags for cp_fold and cp_fold_r. */
> +
> +enum fold_flags {
> + ff_none = 0,
> + /* Whether we're being called from cp_fold_function. */
> + ff_genericize = 1 << 0,
> + /* Whether we're folding late enough that we could assume
> + we're definitely not in a manifestly constant-evaluated
> + context. */
It's not necessarily a matter of late enough; we could fold sooner and
still know that, as in cp_fully_fold_init. We could do the same at
other full-expression points, but we don't because we want to delay
folding as much as possible. So let's say "folding at a point where we
know we're..."
> + ff_mce_false = 1 << 1,
> +};
> +
> +using fold_flags_t = int;
> +
> /* Forward declarations. */
>
> static tree cp_genericize_r (tree *, int *, void *);
> static tree cp_fold_r (tree *, int *, void *);
> static void cp_genericize_tree (tree*, bool);
> -static tree cp_fold (tree);
> +static tree cp_fold (tree, fold_flags_t);
>
> /* Genericize a TRY_BLOCK. */
>
> @@ -1012,9 +1026,8 @@ struct cp_genericize_data
> struct cp_fold_data
> {
> hash_set<tree> pset;
> - bool genericize; // called from cp_fold_function?
> -
> - cp_fold_data (bool g): genericize (g) {}
> + fold_flags_t flags;
> + cp_fold_data (fold_flags_t flags): flags (flags) {}
> };
>
> static tree
> @@ -1055,7 +1068,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
> break;
> }
>
> - *stmt_p = stmt = cp_fold (*stmt_p);
> + *stmt_p = stmt = cp_fold (*stmt_p, data->flags);
>
> if (data->pset.add (stmt))
> {
> @@ -1135,12 +1148,12 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
> here rather than in cp_genericize to avoid problems with the invisible
> reference transition. */
> case INIT_EXPR:
> - if (data->genericize)
> + if (data->flags & ff_genericize)
> cp_genericize_init_expr (stmt_p);
> break;
>
> case TARGET_EXPR:
> - if (data->genericize)
> + if (data->flags & ff_genericize)
> cp_genericize_target_expr (stmt_p);
>
> /* Folding might replace e.g. a COND_EXPR with a TARGET_EXPR; in
> @@ -1173,7 +1186,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
> void
> cp_fold_function (tree fndecl)
> {
> - cp_fold_data data (/*genericize*/true);
> + cp_fold_data data (ff_genericize | ff_mce_false);
Here would be a good place for a comment about passing mce_false because
all manifestly-constant-evaluated expressions will have been
constant-evaluated already if possible.
> cp_walk_tree (&DECL_SAVED_TREE (fndecl), cp_fold_r, &data, NULL);
> }
>
> @@ -2391,7 +2404,7 @@ cp_fold_maybe_rvalue (tree x, bool rval)
> {
> while (true)
> {
> - x = cp_fold (x);
> + x = cp_fold (x, ff_none);
> if (rval)
> x = mark_rvalue_use (x);
> if (rval && DECL_P (x)
> @@ -2450,7 +2463,7 @@ cp_fully_fold_init (tree x)
> if (processing_template_decl)
> return x;
> x = cp_fully_fold (x);
> - cp_fold_data data (/*genericize*/false);
> + cp_fold_data data (ff_mce_false);
> cp_walk_tree (&x, cp_fold_r, &data, NULL);
> return x;
> }
> @@ -2485,7 +2498,7 @@ clear_fold_cache (void)
> Function returns X or its folded variant. */
>
> static tree
> -cp_fold (tree x)
> +cp_fold (tree x, fold_flags_t flags)
> {
> tree op0, op1, op2, op3;
> tree org_x = x, r = NULL_TREE;
> @@ -2506,8 +2519,11 @@ cp_fold (tree x)
> if (fold_cache == NULL)
> fold_cache = hash_map<tree, tree>::create_ggc (101);
>
> - if (tree *cached = fold_cache->get (x))
> - return *cached;
> + bool cache_p = (flags == ff_none);
> +
> + if (cache_p)
> + if (tree *cached = fold_cache->get (x))
> + return *cached;
>
> uid_sensitive_constexpr_evaluation_checker c;
>
> @@ -2542,7 +2558,7 @@ cp_fold (tree x)
> Don't create a new tree if op0 != TREE_OPERAND (x, 0), the
> folding of the operand should be in the caches and if in cp_fold_r
> it will modify it in place. */
> - op0 = cp_fold (TREE_OPERAND (x, 0));
> + op0 = cp_fold (TREE_OPERAND (x, 0), flags);
> if (op0 == error_mark_node)
> x = error_mark_node;
> break;
> @@ -2587,7 +2603,7 @@ cp_fold (tree x)
> {
> tree p = maybe_undo_parenthesized_ref (x);
> if (p != x)
> - return cp_fold (p);
> + return cp_fold (p, flags);
> }
> goto unary;
>
> @@ -2779,8 +2795,8 @@ cp_fold (tree x)
> case COND_EXPR:
> loc = EXPR_LOCATION (x);
> op0 = cp_fold_rvalue (TREE_OPERAND (x, 0));
> - op1 = cp_fold (TREE_OPERAND (x, 1));
> - op2 = cp_fold (TREE_OPERAND (x, 2));
> + op1 = cp_fold (TREE_OPERAND (x, 1), flags);
> + op2 = cp_fold (TREE_OPERAND (x, 2), flags);
>
> if (TREE_CODE (TREE_TYPE (x)) == BOOLEAN_TYPE)
> {
> @@ -2870,7 +2886,7 @@ cp_fold (tree x)
> {
> if (!same_type_p (TREE_TYPE (x), TREE_TYPE (r)))
> r = build_nop (TREE_TYPE (x), r);
> - x = cp_fold (r);
> + x = cp_fold (r, flags);
> break;
> }
> }
> @@ -2890,8 +2906,12 @@ cp_fold (tree x)
> {
> switch (DECL_FE_FUNCTION_CODE (callee))
> {
> - /* Defer folding __builtin_is_constant_evaluated. */
> case CP_BUILT_IN_IS_CONSTANT_EVALUATED:
> + /* Defer folding __builtin_is_constant_evaluated unless
> + we can assume this isn't a manifestly constant-evaluated
s/can assume/know/
OK with those comment changes.
> + context. */
> + if (flags & ff_mce_false)
> + x = boolean_false_node;
> break;
> case CP_BUILT_IN_SOURCE_LOCATION:
> x = fold_builtin_source_location (x);
> @@ -2924,7 +2944,7 @@ cp_fold (tree x)
> int m = call_expr_nargs (x);
> for (int i = 0; i < m; i++)
> {
> - r = cp_fold (CALL_EXPR_ARG (x, i));
> + r = cp_fold (CALL_EXPR_ARG (x, i), flags);
> if (r != CALL_EXPR_ARG (x, i))
> {
> if (r == error_mark_node)
> @@ -2947,7 +2967,7 @@ cp_fold (tree x)
>
> if (TREE_CODE (r) != CALL_EXPR)
> {
> - x = cp_fold (r);
> + x = cp_fold (r, flags);
> break;
> }
>
> @@ -2960,7 +2980,15 @@ cp_fold (tree x)
> constant, but the call followed by an INDIRECT_REF is. */
> if (callee && DECL_DECLARED_CONSTEXPR_P (callee)
> && !flag_no_inline)
> - r = maybe_constant_value (x);
> + {
> + mce_value manifestly_const_eval = mce_unknown;
> + if (flags & ff_mce_false)
> + /* Allow folding __builtin_is_constant_evaluated to false during
> + constexpr evaluation of this call. */
> + manifestly_const_eval = mce_false;
> + r = maybe_constant_value (x, /*decl=*/NULL_TREE,
> + manifestly_const_eval);
> + }
> optimize = sv;
>
> if (TREE_CODE (r) != CALL_EXPR)
> @@ -2987,7 +3015,7 @@ cp_fold (tree x)
> vec<constructor_elt, va_gc> *nelts = NULL;
> FOR_EACH_VEC_SAFE_ELT (elts, i, p)
> {
> - tree op = cp_fold (p->value);
> + tree op = cp_fold (p->value, flags);
> if (op != p->value)
> {
> if (op == error_mark_node)
> @@ -3018,7 +3046,7 @@ cp_fold (tree x)
>
> for (int i = 0; i < n; i++)
> {
> - tree op = cp_fold (TREE_VEC_ELT (x, i));
> + tree op = cp_fold (TREE_VEC_ELT (x, i), flags);
> if (op != TREE_VEC_ELT (x, i))
> {
> if (!changed)
> @@ -3035,10 +3063,10 @@ cp_fold (tree x)
> case ARRAY_RANGE_REF:
>
> loc = EXPR_LOCATION (x);
> - op0 = cp_fold (TREE_OPERAND (x, 0));
> - op1 = cp_fold (TREE_OPERAND (x, 1));
> - op2 = cp_fold (TREE_OPERAND (x, 2));
> - op3 = cp_fold (TREE_OPERAND (x, 3));
> + op0 = cp_fold (TREE_OPERAND (x, 0), flags);
> + op1 = cp_fold (TREE_OPERAND (x, 1), flags);
> + op2 = cp_fold (TREE_OPERAND (x, 2), flags);
> + op3 = cp_fold (TREE_OPERAND (x, 3), flags);
>
> if (op0 != TREE_OPERAND (x, 0)
> || op1 != TREE_OPERAND (x, 1)
> @@ -3066,7 +3094,7 @@ cp_fold (tree x)
> /* A SAVE_EXPR might contain e.g. (0 * i) + (0 * j), which, after
> folding, evaluates to an invariant. In that case no need to wrap
> this folded tree with a SAVE_EXPR. */
> - r = cp_fold (TREE_OPERAND (x, 0));
> + r = cp_fold (TREE_OPERAND (x, 0), flags);
> if (tree_invariant_p (r))
> x = r;
> break;
> @@ -3085,7 +3113,7 @@ cp_fold (tree x)
> copy_warning (x, org_x);
> }
>
> - if (!c.evaluation_restricted_p ())
> + if (cache_p && !c.evaluation_restricted_p ())
> {
> fold_cache->put (org_x, x);
> /* Prevent that we try to fold an already folded result again. */
> diff --git a/gcc/testsuite/g++.dg/opt/is_constant_evaluated1.C b/gcc/testsuite/g++.dg/opt/is_constant_evaluated1.C
> new file mode 100644
> index 00000000000..ee05cbab785
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/opt/is_constant_evaluated1.C
> @@ -0,0 +1,14 @@
> +// PR c++/108243
> +// { dg-do compile { target c++11 } }
> +// { dg-additional-options "-O -fdump-tree-original" }
> +
> +struct A {
> + constexpr A(int n, int m) : n(n), m(m) { }
> + int n, m;
> +};
> +
> +void f(int n) {
> + static A a = {n, __builtin_is_constant_evaluated()};
> +}
> +
> +// { dg-final { scan-tree-dump-not "is_constant_evaluated" "original" } }
> diff --git a/gcc/testsuite/g++.dg/opt/is_constant_evaluated2.C b/gcc/testsuite/g++.dg/opt/is_constant_evaluated2.C
> new file mode 100644
> index 00000000000..ed964e20a7a
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/opt/is_constant_evaluated2.C
> @@ -0,0 +1,32 @@
> +// PR c++/97553
> +// { dg-do compile { target c++11 } }
> +// { dg-additional-options "-O -fdump-tree-original" }
> +
> +constexpr int foo() {
> + return __builtin_is_constant_evaluated() + 1;
> +}
> +
> +#if __cpp_if_consteval
> +constexpr int bar() {
> + if consteval {
> + return 5;
> + } else {
> + return 4;
> + }
> +}
> +#endif
> +
> +int p, q;
> +
> +int main() {
> + p = foo();
> +#if __cpp_if_consteval
> + q = bar();
> +#endif
> +}
> +
> +// { dg-final { scan-tree-dump "p = 1" "original" } }
> +// { dg-final { scan-tree-dump-not "= foo" "original" } }
> +
> +// { dg-final { scan-tree-dump "q = 4" "original" { target c++23 } } }
> +// { dg-final { scan-tree-dump-not "= bar" "original" { target c++23 } } }
next prev parent reply other threads:[~2023-02-05 20:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-27 22:02 [PATCH 1/2] c++: make manifestly_const_eval tri-state Patrick Palka
2023-01-27 22:02 ` [PATCH 2/2] c++: speculative constexpr and is_constant_evaluated [PR108243] Patrick Palka
2023-01-27 22:05 ` Patrick Palka
2023-01-30 20:05 ` Jason Merrill
2023-02-03 20:51 ` Patrick Palka
2023-02-03 20:57 ` Patrick Palka
2023-02-05 20:11 ` Jason Merrill [this message]
2023-02-09 17:36 ` Patrick Palka
2023-02-09 23:36 ` Jason Merrill
2023-02-10 1:32 ` Patrick Palka
2023-02-10 14:48 ` Patrick Palka
2023-02-10 16:51 ` Patrick Palka
2023-02-14 23:02 ` Jason Merrill
2023-01-30 20:02 ` [PATCH 1/2] c++: make manifestly_const_eval tri-state Jason Merrill
2023-02-03 21:21 ` Patrick Palka
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