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* [gcc r13-6395] c++: unevaluated array new-expr size constantness [PR108219]
@ 2023-03-01 19:09 Patrick Palka
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From: Patrick Palka @ 2023-03-01 19:09 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:096f034a8f5df41f610e62c1592fb90a3f551cd5
commit r13-6395-g096f034a8f5df41f610e62c1592fb90a3f551cd5
Author: Patrick Palka <ppalka@redhat.com>
Date: Wed Mar 1 14:09:37 2023 -0500
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 <jason@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.
Diff:
---
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(-)
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>);
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