From 096f034a8f5df41f610e62c1592fb90a3f551cd5 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Wed, 1 Mar 2023 14:09:37 -0500 Subject: c++: unevaluated array new-expr size constantness [PR108219] Here we're mishandling the unevaluated array new-expressions due to a supposed non-constant array size ever since r12-5253-g4df7f8c79835d569 made us no longer perform constant evaluation of non-manifestly-constant expressions within unevaluated contexts. This shouldn't make a difference here since the array sizes are constant literals, except they're expressed as NON_LVALUE_EXPR location wrappers around INTEGER_CST, wrappers which used to get stripped as part of constant evaluation and now no longer do. Moreover it means build_vec_init can't constant fold the MINUS_EXPR 'maxindex' passed from build_new_1 when in an unevaluated context (since it tries reducing it via maybe_constant_value called with mce_unknown). This patch fixes these issues by making maybe_constant_value (and fold_non_dependent_expr) try folding an unevaluated non-manifestly-constant operand via fold(), as long as it simplifies to a simple constant, rather than doing no simplification at all. This covers e.g. simple arithmetic and casts including stripping of location wrappers around INTEGER_CST. In passing, this patch also fixes maybe_constant_value to avoid constant evaluating an unevaluated operand when called with mce_false, by adjusting the early exit test appropriately. Co-authored-by: Jason Merrill PR c++/108219 PR c++/108218 gcc/cp/ChangeLog: * constexpr.cc (fold_to_constant): Define. (maybe_constant_value): Move up early exit test for unevaluated operands. Try reducing an unevaluated operand to a constant via fold_to_constant. (fold_non_dependent_expr_template): Add early exit test for CONSTANT_CLASS_P nodes. Try reducing an unevaluated operand to a constant via fold_to_constant. * cp-tree.h (fold_to_constant): Declare. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/new6.C: New test. * g++.dg/cpp2a/concepts-new1.C: New test. --- gcc/cp/constexpr.cc | 29 ++++++++++++++++++++++++----- 1 file changed, 24 insertions(+), 5 deletions(-) (limited to 'gcc/cp/constexpr.cc') diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index 89df7d76..bcae1cb 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -8498,6 +8498,19 @@ fold_simple (tree t) return t; } +/* Try folding the expression T to a simple constant. + Returns that constant, otherwise returns T. */ + +tree +fold_to_constant (tree t) +{ + tree r = fold (t); + if (CONSTANT_CLASS_P (r) && !TREE_OVERFLOW (r)) + return r; + else + return t; +} + /* If T is a constant expression, returns its reduced value. Otherwise, if T does not have TREE_CONSTANT set, returns T. Otherwise, returns a version of T without TREE_CONSTANT. @@ -8523,6 +8536,11 @@ maybe_constant_value (tree t, tree decl /* = NULL_TREE */, /* No caching or evaluation needed. */ return t; + /* Don't constant evaluate an unevaluated non-manifestly-constant operand, + but at least try folding it to a simple constant. */ + if (cp_unevaluated_operand && manifestly_const_eval != mce_true) + return fold_to_constant (t); + if (manifestly_const_eval != mce_unknown) return cxx_eval_outermost_constant_expr (t, true, true, manifestly_const_eval, false, decl); @@ -8544,10 +8562,6 @@ maybe_constant_value (tree t, tree decl /* = NULL_TREE */, return r; } - /* Don't evaluate an unevaluated operand. */ - if (cp_unevaluated_operand) - return t; - uid_sensitive_constexpr_evaluation_checker c; r = cxx_eval_outermost_constant_expr (t, true, true, manifestly_const_eval, false, decl); @@ -8611,9 +8625,14 @@ fold_non_dependent_expr_template (tree t, tsubst_flags_t complain, } return t; } + else if (CONSTANT_CLASS_P (t)) + /* No evaluation needed. */ + return t; + /* Don't constant evaluate an unevaluated non-manifestly-constant operand, + but at least try folding it to a simple constant. */ if (cp_unevaluated_operand && !manifestly_const_eval) - return t; + return fold_to_constant (t); tree r = cxx_eval_outermost_constant_expr (t, true, true, mce_value (manifestly_const_eval), -- cgit v1.1