From e408261123697a82b5965c700fa2465999f0fd62 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Wed, 8 Aug 2018 11:00:51 +0200 Subject: [PATCH] P0595R1 - is_constant_evaluated P0595R1 - is_constant_evaluated cp/ * cp-tree.h (enum cp_built_in_function): New. (maybe_constant_init): Add pretend_const_required argument. * typeck2.c (store_init_value): Pass true as new argument to maybe_constant_init. * constexpr.c (constexpr_fn_retval): Check also DECL_BUILT_IN_CLASS for BUILT_IN_UNREACHABLE. (struct constexpr_ctx): Add pretend_const_required field. (cxx_eval_builtin_function_call): Use DECL_IS_BUILTIN_CONSTANT_P macro. Handle CP_BUILT_IN_IS_CONSTANT_EVALUATED. Check also DECL_BUILT_IN_CLASS for BUILT_IN_UNREACHABLE. (cxx_eval_outermost_constant_expr): Add pretend_const_required argument, initialize pretend_const_required field in ctx. If the result is TREE_CONSTANT and non_constant_p, retry with pretend_const_required false if it was true. (is_sub_constant_expr): Initialize pretend_const_required_field in ctx. (cxx_constant_value): Pass true as pretend_const_required to cxx_eval_outermost_constant_expr. (maybe_constant_value): Pass false as pretend_const_required to cxx_eval_outermost_constant_expr. (fold_non_dependent_expr): Likewise. (maybe_constant_init_1): Add pretend_const_required argument, pass it down to cxx_eval_outermost_constant_expr. Pass !allow_non_constant instead of false as strict to cxx_eval_outermost_constant_expr. (maybe_constant_init): Add pretend_const_required argument, pass it down to maybe_constant_init_1. (cxx_constant_init): Pass true as pretend_const_required to maybe_constant_init_1. * cp-gimplify.c (cp_gimplify_expr): Handle CALL_EXPRs to CP_BUILT_IN_IS_CONSTANT_EVALUATED. (cp_fold): Don't fold CP_BUILT_IN_IS_CONSTANT_EVALUATED calls. * decl.c: Include langhooks.h. (cxx_init_decl_processing): Register __builtin_is_constant_evaluated built-in. * tree.c (builtin_valid_in_constant_expr_p): Return true for CP_BUILT_IN_IS_CONSTANT_EVALUATED. * pt.c (declare_integer_pack): Initialize DECL_FUNCTION_CODE. testsuite/ * g++.dg/cpp2a/is-constant-evaluated1.C: New test. From-SVN: r263392 --- gcc/cp/ChangeLog | 39 +++++++++++ gcc/cp/constexpr.c | 66 +++++++++++++++---- gcc/cp/cp-gimplify.c | 16 +++++ gcc/cp/cp-tree.h | 9 ++- gcc/cp/decl.c | 8 +++ gcc/cp/pt.c | 2 + gcc/cp/tree.c | 14 +++- gcc/cp/typeck2.c | 2 +- gcc/testsuite/ChangeLog | 3 + .../g++.dg/cpp2a/is-constant-evaluated1.C | 66 +++++++++++++++++++ 10 files changed, 206 insertions(+), 19 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated1.C diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog index a6bdc043b05..8a3e1507704 100644 --- a/gcc/cp/ChangeLog +++ b/gcc/cp/ChangeLog @@ -1,5 +1,44 @@ 2018-08-08 Jakub Jelinek + P0595R1 - is_constant_evaluated + * cp-tree.h (enum cp_built_in_function): New. + (maybe_constant_init): Add pretend_const_required argument. + * typeck2.c (store_init_value): Pass true as new argument to + maybe_constant_init. + * constexpr.c (constexpr_fn_retval): Check also DECL_BUILT_IN_CLASS + for BUILT_IN_UNREACHABLE. + (struct constexpr_ctx): Add pretend_const_required field. + (cxx_eval_builtin_function_call): Use DECL_IS_BUILTIN_CONSTANT_P + macro. Handle CP_BUILT_IN_IS_CONSTANT_EVALUATED. Check also + DECL_BUILT_IN_CLASS for BUILT_IN_UNREACHABLE. + (cxx_eval_outermost_constant_expr): Add pretend_const_required + argument, initialize pretend_const_required field in ctx. If the + result is TREE_CONSTANT and non_constant_p, retry with + pretend_const_required false if it was true. + (is_sub_constant_expr): Initialize pretend_const_required_field in + ctx. + (cxx_constant_value): Pass true as pretend_const_required to + cxx_eval_outermost_constant_expr. + (maybe_constant_value): Pass false as pretend_const_required to + cxx_eval_outermost_constant_expr. + (fold_non_dependent_expr): Likewise. + (maybe_constant_init_1): Add pretend_const_required argument, pass it + down to cxx_eval_outermost_constant_expr. Pass !allow_non_constant + instead of false as strict to cxx_eval_outermost_constant_expr. + (maybe_constant_init): Add pretend_const_required argument, pass it + down to maybe_constant_init_1. + (cxx_constant_init): Pass true as pretend_const_required to + maybe_constant_init_1. + * cp-gimplify.c (cp_gimplify_expr): Handle CALL_EXPRs to + CP_BUILT_IN_IS_CONSTANT_EVALUATED. + (cp_fold): Don't fold CP_BUILT_IN_IS_CONSTANT_EVALUATED calls. + * decl.c: Include langhooks.h. + (cxx_init_decl_processing): Register __builtin_is_constant_evaluated + built-in. + * tree.c (builtin_valid_in_constant_expr_p): Return true for + CP_BUILT_IN_IS_CONSTANT_EVALUATED. + * pt.c (declare_integer_pack): Initialize DECL_FUNCTION_CODE. + PR c++/86836 * pt.c (tsubst_expr): For structured bindings, call tsubst_decomp_names before tsubst_init, not after it. diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index d796e8b1626..ece2c8a92d9 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -713,6 +713,7 @@ constexpr_fn_retval (tree body) { tree fun = get_function_named_in_call (body); if (fun != NULL_TREE + && DECL_BUILT_IN_CLASS (fun) == BUILT_IN_NORMAL && DECL_FUNCTION_CODE (fun) == BUILT_IN_UNREACHABLE) return NULL_TREE; } @@ -1007,6 +1008,8 @@ struct constexpr_ctx { /* Whether we are strictly conforming to constant expression rules or trying harder to get a constant value. */ bool strict; + /* Whether __builtin_is_constant_evaluated () should be true. */ + bool pretend_const_required; }; /* A table of all constexpr calls that have been evaluated by the @@ -1171,7 +1174,7 @@ cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun, int i; /* Don't fold __builtin_constant_p within a constexpr function. */ - bool bi_const_p = (DECL_FUNCTION_CODE (fun) == BUILT_IN_CONSTANT_P); + bool bi_const_p = DECL_IS_BUILTIN_CONSTANT_P (fun); /* If we aren't requiring a constant expression, defer __builtin_constant_p in a constexpr function until we have values for the parameters. */ @@ -1184,6 +1187,19 @@ cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun, return t; } + /* For __builtin_is_constant_evaluated, defer it if not + ctx->pretend_const_required, otherwise fold it to true. */ + if (DECL_BUILT_IN_CLASS (fun) == BUILT_IN_FRONTEND + && (int) DECL_FUNCTION_CODE (fun) == CP_BUILT_IN_IS_CONSTANT_EVALUATED) + { + if (!ctx->pretend_const_required) + { + *non_constant_p = true; + return t; + } + return boolean_true_node; + } + /* Be permissive for arguments to built-ins; __builtin_constant_p should return constant false for a non-constant argument. */ constexpr_ctx new_ctx = *ctx; @@ -1217,7 +1233,8 @@ cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun, /* Do not allow__builtin_unreachable in constexpr function. The __builtin_unreachable call with BUILTINS_LOCATION comes from cp_maybe_instrument_return. */ - if (DECL_FUNCTION_CODE (fun) == BUILT_IN_UNREACHABLE + if (DECL_BUILT_IN_CLASS (fun) == BUILT_IN_NORMAL + && DECL_FUNCTION_CODE (fun) == BUILT_IN_UNREACHABLE && EXPR_LOCATION (t) == BUILTINS_LOCATION) error ("% call flows off the end of the function"); else @@ -4897,9 +4914,15 @@ instantiate_constexpr_fns (tree t) input_location = loc; } +/* ALLOW_NON_CONSTANT is false if T is required to be a constant expression. + PRETEND_CONST_REQUIRED is true if T is required to be const-evaluated as + per P0595 even when ALLOW_NON_CONSTANT is true. */ + static tree cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant, - bool strict = true, tree object = NULL_TREE) + bool strict = true, + bool pretend_const_required = false, + tree object = NULL_TREE) { auto_timevar time (TV_CONSTEXPR); @@ -4908,7 +4931,8 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant, hash_map map; constexpr_ctx ctx = { NULL, &map, NULL, NULL, NULL, NULL, - allow_non_constant, strict }; + allow_non_constant, strict, + pretend_const_required || !allow_non_constant }; tree type = initialized_type (t); tree r = t; @@ -4997,6 +5021,12 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant, return error_mark_node; else if (non_constant_p && TREE_CONSTANT (r)) { + /* If __builtin_is_constant_evaluated () was evaluated to true + and the result is not a valid constant expression, we need to + punt. */ + if (pretend_const_required) + return cxx_eval_outermost_constant_expr (t, true, strict, + false, object); /* This isn't actually constant, so unset TREE_CONSTANT. Don't clear TREE_CONSTANT on ADDR_EXPR, as the middle-end requires it to be set if it is invariant address, even when it is not @@ -5042,7 +5072,8 @@ is_sub_constant_expr (tree t) bool overflow_p = false; hash_map map; - constexpr_ctx ctx = { NULL, &map, NULL, NULL, NULL, NULL, true, true }; + constexpr_ctx ctx + = { NULL, &map, NULL, NULL, NULL, NULL, true, true, false }; instantiate_constexpr_fns (t); cxx_eval_constant_expression (&ctx, t, false, &non_constant_p, @@ -5057,7 +5088,7 @@ is_sub_constant_expr (tree t) tree cxx_constant_value (tree t, tree decl) { - return cxx_eval_outermost_constant_expr (t, false, true, decl); + return cxx_eval_outermost_constant_expr (t, false, true, true, decl); } /* Helper routine for fold_simple function. Either return simplified @@ -5163,7 +5194,7 @@ maybe_constant_value (tree t, tree decl) if (tree *cached = cv_cache->get (t)) return *cached; - r = cxx_eval_outermost_constant_expr (t, true, true, decl); + r = cxx_eval_outermost_constant_expr (t, true, true, false, decl); gcc_checking_assert (r == t || CONVERT_EXPR_P (t) || TREE_CODE (t) == VIEW_CONVERT_EXPR @@ -5237,7 +5268,8 @@ fold_non_dependent_expr (tree t, return t; } - tree r = cxx_eval_outermost_constant_expr (t, true, true, NULL_TREE); + tree r = cxx_eval_outermost_constant_expr (t, true, true, false, + NULL_TREE); /* cp_tree_equal looks through NOPs, so allow them. */ gcc_checking_assert (r == t || CONVERT_EXPR_P (t) @@ -5258,10 +5290,14 @@ fold_non_dependent_expr (tree t, } /* Like maybe_constant_value, but returns a CONSTRUCTOR directly, rather - than wrapped in a TARGET_EXPR. */ + than wrapped in a TARGET_EXPR. + ALLOW_NON_CONSTANT is false if T is required to be a constant expression. + PRETEND_CONST_REQUIRED is true if T is required to be const-evaluated as + per P0595 even when ALLOW_NON_CONSTANT is true. */ static tree -maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant) +maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant, + bool pretend_const_required) { if (!t) return t; @@ -5279,7 +5315,9 @@ maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant) else if (CONSTANT_CLASS_P (t) && allow_non_constant) /* No evaluation needed. */; else - t = cxx_eval_outermost_constant_expr (t, allow_non_constant, false, decl); + t = cxx_eval_outermost_constant_expr (t, allow_non_constant, + !allow_non_constant, + pretend_const_required, decl); if (TREE_CODE (t) == TARGET_EXPR) { tree init = TARGET_EXPR_INITIAL (t); @@ -5292,9 +5330,9 @@ maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant) /* Wrapper for maybe_constant_init_1 which permits non constants. */ tree -maybe_constant_init (tree t, tree decl) +maybe_constant_init (tree t, tree decl, bool pretend_const_required) { - return maybe_constant_init_1 (t, decl, true); + return maybe_constant_init_1 (t, decl, true, pretend_const_required); } /* Wrapper for maybe_constant_init_1 which does not permit non constants. */ @@ -5302,7 +5340,7 @@ maybe_constant_init (tree t, tree decl) tree cxx_constant_init (tree t, tree decl) { - return maybe_constant_init_1 (t, decl, false); + return maybe_constant_init_1 (t, decl, false, true); } #if 0 diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c index 28802b5a3be..7db4accb504 100644 --- a/gcc/cp/cp-gimplify.c +++ b/gcc/cp/cp-gimplify.c @@ -793,6 +793,15 @@ cp_gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p) ret = GS_ERROR; } } + if (ret != GS_ERROR) + { + tree decl = cp_get_callee_fndecl_nofold (*expr_p); + if (decl + && DECL_BUILT_IN_CLASS (decl) == BUILT_IN_FRONTEND + && ((int) DECL_FUNCTION_CODE (decl) + == CP_BUILT_IN_IS_CONSTANT_EVALUATED)) + *expr_p = boolean_false_node; + } break; case RETURN_EXPR: @@ -2483,6 +2492,13 @@ cp_fold (tree x) && DECL_DECLARED_CONSTEXPR_P (current_function_decl)) nw = 1; + /* Defer folding __builtin_is_constant_evaluated. */ + if (callee + && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_FRONTEND + && ((int) DECL_FUNCTION_CODE (callee) + == CP_BUILT_IN_IS_CONSTANT_EVALUATED)) + break; + x = copy_node (x); m = call_expr_nargs (x); diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index d225702e42f..94a85b72d2b 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -5966,6 +5966,13 @@ struct GTY((chain_next ("%h.next"))) tinst_level { static const unsigned short refcount_infinity = (unsigned short) ~0; }; +/* BUILT_IN_FRONTEND function codes. */ +enum cp_built_in_function { + CP_BUILT_IN_IS_CONSTANT_EVALUATED, + CP_BUILT_IN_INTEGER_PACK, + CP_BUILT_IN_LAST +}; + bool decl_spec_seq_has_spec_p (const cp_decl_specifier_seq *, cp_decl_spec); /* Return the type of the `this' parameter of FNTYPE. */ @@ -7572,7 +7579,7 @@ extern bool require_potential_rvalue_constant_expression (tree); extern tree cxx_constant_value (tree, tree = NULL_TREE); extern tree cxx_constant_init (tree, tree = NULL_TREE); extern tree maybe_constant_value (tree, tree = NULL_TREE); -extern tree maybe_constant_init (tree, tree = NULL_TREE); +extern tree maybe_constant_init (tree, tree = NULL_TREE, bool = false); extern tree fold_non_dependent_expr (tree, tsubst_flags_t = tf_warning_or_error); extern tree fold_simple (tree); extern bool is_sub_constant_expr (tree); diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c index 0efb42e0f20..78ebbde61a3 100644 --- a/gcc/cp/decl.c +++ b/gcc/cp/decl.c @@ -52,6 +52,7 @@ along with GCC; see the file COPYING3. If not see #include "gimplify.h" #include "asan.h" #include "gcc-rich-location.h" +#include "langhooks.h" /* Possible cases of bad specifiers type used by bad_specifiers. */ enum bad_spec_place { @@ -4172,6 +4173,13 @@ cxx_init_decl_processing (void) c_common_nodes_and_builtins (); + tree bool_ftype = build_function_type_list (boolean_type_node, NULL_TREE); + tree decl + = add_builtin_function ("__builtin_is_constant_evaluated", + bool_ftype, CP_BUILT_IN_IS_CONSTANT_EVALUATED, + BUILT_IN_FRONTEND, NULL, NULL_TREE); + set_call_expr_flags (decl, ECF_CONST | ECF_NOTHROW | ECF_LEAF); + integer_two_node = build_int_cst (NULL_TREE, 2); /* Guess at the initial static decls size. */ diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index 0a5d112986f..7fcf5d6b2d3 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -27538,6 +27538,8 @@ declare_integer_pack (void) NULL_TREE, ECF_CONST); DECL_DECLARED_CONSTEXPR_P (ipfn) = true; DECL_BUILT_IN_CLASS (ipfn) = BUILT_IN_FRONTEND; + DECL_FUNCTION_CODE (ipfn) + = (enum built_in_function) (int) CP_BUILT_IN_INTEGER_PACK; } /* Set up the hash tables for template instantiations. */ diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c index 7e2a77bf67b..1cf3269d880 100644 --- a/gcc/cp/tree.c +++ b/gcc/cp/tree.c @@ -415,10 +415,18 @@ cp_stabilize_reference (tree ref) bool builtin_valid_in_constant_expr_p (const_tree decl) { - if (!(TREE_CODE (decl) == FUNCTION_DECL - && DECL_BUILT_IN_CLASS (decl) == BUILT_IN_NORMAL)) - /* Not a built-in. */ + if (TREE_CODE (decl) != FUNCTION_DECL) + /* Not a function. */ return false; + if (DECL_BUILT_IN_CLASS (decl) != BUILT_IN_NORMAL) + { + if (DECL_BUILT_IN_CLASS (decl) == BUILT_IN_FRONTEND + && ((int) DECL_FUNCTION_CODE (decl) + == CP_BUILT_IN_IS_CONSTANT_EVALUATED)) + return true; + /* Not a built-in. */ + return false; + } switch (DECL_FUNCTION_CODE (decl)) { /* These always have constant results like the corresponding diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c index 91aa5a62856..7763d53ee65 100644 --- a/gcc/cp/typeck2.c +++ b/gcc/cp/typeck2.c @@ -837,7 +837,7 @@ store_init_value (tree decl, tree init, vec** cleanups, int flags) value = cxx_constant_init (value, decl); } else - value = maybe_constant_init (value, decl); + value = maybe_constant_init (value, decl, true); if (TREE_CODE (value) == CONSTRUCTOR && cp_has_mutable_p (type)) /* Poison this CONSTRUCTOR so it can't be copied to another constexpr variable. */ diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index e614fed960a..c729af8687e 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,5 +1,8 @@ 2018-08-08 Jakub Jelinek + P0595R1 - is_constant_evaluated + * g++.dg/cpp2a/is-constant-evaluated1.C: New test. + PR c++/86836 * g++.dg/cpp1z/decomp46.C: New test. diff --git a/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated1.C b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated1.C new file mode 100644 index 00000000000..3b988845e41 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated1.C @@ -0,0 +1,66 @@ +// P0595R1 +// { dg-do compile { target c++14 } } + +template struct X { int v = N; }; +X<__builtin_is_constant_evaluated ()> x; // type X +int y = 4; +int a = __builtin_is_constant_evaluated () ? y : 1; // initializes a to 1 +int b = __builtin_is_constant_evaluated () ? 2 : y; // initializes b to 2 +int c = y + (__builtin_is_constant_evaluated () ? 2 : y); // initializes c to 2*y +int d = __builtin_is_constant_evaluated (); // initializes d to 1 +int e = d + __builtin_is_constant_evaluated (); // initializes e to 0 + +struct false_type { static constexpr bool value = false; }; +struct true_type { static constexpr bool value = true; }; +template +struct is_same : false_type {}; +template +struct is_same : true_type {}; + +constexpr int +foo (int x) +{ + const int n = __builtin_is_constant_evaluated () ? 13 : 17; // n == 13 + int m = __builtin_is_constant_evaluated () ? 13 : 17; // m might be 13 or 17 (see below) + char arr[n] = {}; // char[13] + return m + sizeof (arr) + x; +} + +constexpr int +bar () +{ + const int n = __builtin_is_constant_evaluated() ? 13 : 17; + X x1; + X<__builtin_is_constant_evaluated() ? 13 : 17> x2; + static_assert (is_same::value, "x1/x2's type"); + return x1.v + x2.v; +} + +int p = foo (0); // m == 13; initialized to 26 +int q = p + foo (0); // m == 17 for this call; initialized to 56 +static_assert (bar () == 26, "bar"); + +struct S { int a, b; }; + +S s = { __builtin_is_constant_evaluated () ? 2 : 3, y }; +S t = { __builtin_is_constant_evaluated () ? 2 : 3, 4 }; + +static_assert (is_same >::value, "x's type"); + +int +main () +{ + if (a != 1 || b != 2 || c != 8 || d != 1 || e != 0 || p != 26 || q != 56) + __builtin_abort (); + if (s.a != 3 || s.b != 4 || t.a != 2 || t.b != 4) + __builtin_abort (); + if (foo (y) != 34) + __builtin_abort (); +#if __cplusplus >= 201703L + if constexpr (foo (0) != 26) + __builtin_abort (); +#endif + constexpr int w = foo (0); + if (w != 26) + __builtin_abort (); +} -- 2.30.2