On Mon, 27 Feb 2023, Jason Merrill wrote: > On 2/22/23 14:45, Patrick Palka wrote: > > 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 actually NON_LVALUE_EXPR location wrappers wrapping 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 'maxindex' passed from build_new_1 (since it uses maybe_constant_value > > with mce_unknown). > > Hmm, now that you mention it I think the > > if (manifestly_const_eval != mce_unknown) > > change in maybe_constant_value isn't quite right, we don't want to force > evaluation in unevaluated mce_false context either.
Ah, makes sense. Fixed in the below patch. > > > This patch fixes the first issue by making maybe_constant_value and > > fold_non_dependent_expr_template shortcut handling location wrappers > > around constant nodes, and the second issue by using fold_build2_loc > > instead of cp_build_binary_op when computing the maxindex to pass to > > build_vec_init. > > Maybe in unevaluated mce_unknown/false context maybe_constant_value should > call fold? That seems like a good compromise between proper constant evaluation and not constant evaluating at all, though I wonder how 'fold' behaves w.r.t. to undefined behavior such as division by zero and signed overflow? IIUC proper constant evaluation treats UB as non-constant, so it might be potentially problematic if 'fold' instea dtakes advantage of UB. Or maybe since we're in an unevaluated context it doesn't matter? -- >8 -- Subject: [PATCH] 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 these sizes are 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 'maxindex' passed from build_new_1 (since it uses maybe_constant_value with mce_unknown). This patch fixes this by making maybe_constant_value and fold_non_dependent_expr at least try folding simple unevaluated operands via fold(), which will evaluate simple arithmetic, look through location wrappers, perform integral conversions, etc. Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for trunk/12? PR c++/108219 PR c++/108218 gcc/cp/ChangeLog: * constexpr.cc (maybe_constant_value): Move up early exit test for unevaluated operands. Call fold on unevaluated operands. (fold_non_dependent_expr_template): Add early exit test for CONSTANT_CLASS_P nodes. Call fold on unevaluated operands. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/new6.C: New test. * g++.dg/cpp2a/concepts-new1.C: New test. --- gcc/cp/constexpr.cc | 17 ++++++++++++----- gcc/testsuite/g++.dg/cpp0x/new6.C | 13 +++++++++++++ gcc/testsuite/g++.dg/cpp2a/concepts-new1.C | 13 +++++++++++++ 3 files changed, 38 insertions(+), 5 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/new6.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-new1.C diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index b4d3e95bbd5..d71abe6beed 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -8523,6 +8523,11 @@ 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 simple expressions. */ + if (cp_unevaluated_operand && manifestly_const_eval != mce_true) + return fold (t); + if (manifestly_const_eval != mce_unknown) return cxx_eval_outermost_constant_expr (t, true, true, manifestly_const_eval, false, decl); @@ -8544,10 +8549,6 @@ 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); @@ -8612,8 +8613,14 @@ fold_non_dependent_expr_template (tree t, tsubst_flags_t complain, return t; } + 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 simple expressions. */ if (cp_unevaluated_operand && !manifestly_const_eval) - return t; + return fold (t); tree r = cxx_eval_outermost_constant_expr (t, true, true, mce_value (manifestly_const_eval), diff --git a/gcc/testsuite/g++.dg/cpp0x/new6.C b/gcc/testsuite/g++.dg/cpp0x/new6.C new file mode 100644 index 00000000000..d8f11441423 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/new6.C @@ -0,0 +1,13 @@ +// PR c++/108218 +// { dg-do compile { target c++11 } } + +template<class T> +void f() { + decltype(new int[-1]) p; // { dg-error "negative" } + decltype(new int[0-1]) q; // { dg-error "negative" } + decltype(new int[1*-1]) r; // { dg-error "negative" } +} + +decltype(new int[-1]) p; // { dg-error "negative" } +decltype(new int[0-1]) q; // { dg-error "negative" } +decltype(new int[1*-1]) r; // { dg-error "negative" } diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-new1.C b/gcc/testsuite/g++.dg/cpp2a/concepts-new1.C new file mode 100644 index 00000000000..62007205108 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-new1.C @@ -0,0 +1,13 @@ +// PR c++/108219 +// { dg-do compile { target c++20 } } + +template<class T> +concept C = requires { new T[1]{{ 42 }}; }; + +template<class T> +concept D = requires { new T[2][1]{{{ 42 }}, {{ 42 }}}; }; + +struct A { A(int); }; + +static_assert(C<A>); +static_assert(D<A>); -- 2.40.0.rc0.57.g454dfcbddf