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.
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>);
