diff options
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/cp/constexpr.c | 26 | ||||
| -rw-r--r-- | gcc/testsuite/g++.dg/cpp1z/fold13.C | 29 |
2 files changed, 50 insertions, 5 deletions
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index a31d12b..40fe165 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -8892,13 +8892,18 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, tmp = boolean_false_node; truth: { - tree op = TREE_OPERAND (t, 0); - if (!RECUR (op, rval)) + tree op0 = TREE_OPERAND (t, 0); + tree op1 = TREE_OPERAND (t, 1); + if (!RECUR (op0, rval)) return false; + if (!(flags & tf_error) && RECUR (op1, rval)) + /* When quiet, try to avoid expensive trial evaluation by first + checking potentiality of the second operand. */ + return true; if (!processing_template_decl) - op = cxx_eval_outermost_constant_expr (op, true); - if (tree_int_cst_equal (op, tmp)) - return RECUR (TREE_OPERAND (t, 1), rval); + op0 = cxx_eval_outermost_constant_expr (op0, true); + if (tree_int_cst_equal (op0, tmp)) + return (flags & tf_error) ? RECUR (op1, rval) : false; else return true; } @@ -9107,6 +9112,17 @@ bool potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, tsubst_flags_t flags) { + if (flags & tf_error) + { + /* Check potentiality quietly first, as that could be performed more + efficiently in some cases (currently only for TRUTH_*_EXPR). If + that fails, replay the check noisily to give errors. */ + flags &= ~tf_error; + if (potential_constant_expression_1 (t, want_rval, strict, now, flags)) + return true; + flags |= tf_error; + } + tree target = NULL_TREE; return potential_constant_expression_1 (t, want_rval, strict, now, flags, &target); diff --git a/gcc/testsuite/g++.dg/cpp1z/fold13.C b/gcc/testsuite/g++.dg/cpp1z/fold13.C new file mode 100644 index 0000000..9d7554f --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/fold13.C @@ -0,0 +1,29 @@ +// { dg-do compile { target c++17 } } +// Verify constexpr evaluation of a large left fold logical expression +// isn't quadratic in the size of the expanded expression. + +template<int> struct S { static constexpr bool value = true; }; + +template<class T, T...> struct integer_sequence { }; + +template<class T, T N> +using make_integer_sequence +#if __has_builtin(__make_integer_seq) + = __make_integer_seq<integer_sequence, T, N>; +#else + = integer_sequence<T, __integer_pack(N)...>; +#endif + +template<int... Is> +constexpr bool f_impl(integer_sequence<int, Is...>) { + return (... && S<Is>::value); +} + +static_assert(f_impl(make_integer_sequence<int, 1024>())); + +template<int... Is> +constexpr bool g_impl(integer_sequence<int, Is...>) { + return (... || !S<Is>::value); +} + +static_assert(!g_impl(make_integer_sequence<int, 1024>())); |