On Wed, 1 Mar 2023, Jason Merrill wrote: > On 3/1/23 12:20, Patrick Palka wrote: > > On Wed, 1 Mar 2023, Jason Merrill wrote: > > > > > On 3/1/23 10:32, Patrick Palka wrote: > > > > 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? > > > > > > 'fold' doesn't fold division by zero, but I think we should only return > > > the > > > result of 'fold' at this point if it is in fact constant, not if it's a > > > non-constant simplification. > > > > Sounds good, I wasn't sure if 'fold' could return a non-constant > > simplification. > > Yep, it also folds e.g. x*1 to x. > > > I suppose we want to be pretty conservative with the > > constantness test, so I went with CONSTANT_CLASS_P && !TREE_OVERFLOW. > > Makes sense. > > > Like so? Smoke tested so far, bootstrap and regtest on > > x86_64-pc-linu-xgnu in progress. > > > > -- >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. > > > > Co-authored-by: Jason Merrill <ja...@redhat.com> > > > > 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. Try reducing an unevaluated > > operand to a constant via fold. > > (fold_non_dependent_expr_template): Add early exit test for > > CONSTANT_CLASS_P nodes. Try reducing an unevaluated operand > > to a constant via fold. > > > > gcc/testsuite/ChangeLog: > > > > * g++.dg/cpp0x/new6.C: New test. > > * g++.dg/cpp2a/concepts-new1.C: New test. > > --- > > gcc/cp/constexpr.cc | 23 +++++++++++++++++----- > > gcc/testsuite/g++.dg/cpp0x/new6.C | 13 ++++++++++++ > > gcc/testsuite/g++.dg/cpp2a/concepts-new1.C | 13 ++++++++++++ > > 3 files changed, 44 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..324968050ba 100644 > > --- a/gcc/cp/constexpr.cc > > +++ b/gcc/cp/constexpr.cc > > @@ -8523,6 +8523,14 @@ 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 to a constant. */ > > + if (cp_unevaluated_operand && manifestly_const_eval != mce_true) > > + { > > + tree r = fold (t); > > + return CONSTANT_CLASS_P (r) && !TREE_OVERFLOW (r) ? r : t; > > + } > > + > > if (manifestly_const_eval != mce_unknown) > > return cxx_eval_outermost_constant_expr (t, true, true, > > manifestly_const_eval, false, > > decl); > > @@ -8544,10 +8552,6 @@ 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 +8616,17 @@ 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 to a constant. */ > > if (cp_unevaluated_operand && !manifestly_const_eval) > > - return t; > > + { > > + tree r = fold (t); > > + return CONSTANT_CLASS_P (r) && !TREE_OVERFLOW (r) ? r : t; > > These two lines could be factored into a fold_to_constant (inline?) function. > OK with that change.
Thanks a lot, I went with a non-inline function to avoid introducing a direct dependency on fold-const.h from cp-tree.h (though somehow defining it inline worked too without needing to directly #include fold-const.h from cp-tree.h). Here's what I pushed: -- >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 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 <ja...@redhat.com> 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 ++++++++++++++++++---- gcc/cp/cp-tree.h | 1 + gcc/testsuite/g++.dg/cpp0x/new6.C | 13 ++++++++++ gcc/testsuite/g++.dg/cpp2a/concepts-new1.C | 13 ++++++++++ 4 files changed, 51 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 89df7d7600c..bcae1cbd973 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), diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index 5595335bbf7..83633ddc7f2 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -8516,6 +8516,7 @@ extern tree fold_non_dependent_init (tree, tsubst_flags_t = tf_warning_or_error, bool = false, tree = NULL_TREE); extern tree fold_simple (tree); +extern tree fold_to_constant (tree); extern bool reduced_constant_expression_p (tree); extern bool is_instantiation_of_constexpr (tree); extern bool var_in_constexpr_fn (tree); 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