* [PATCH] libstdc++: Remove overzealous static_asserts from std::span
@ 2020-09-21 18:45 Patrick Palka
2020-09-21 19:07 ` Patrick Palka
0 siblings, 1 reply; 3+ messages in thread
From: Patrick Palka @ 2020-09-21 18:45 UTC (permalink / raw)
To: gcc-patches; +Cc: libstdc++, Patrick Palka
For a span with empty static extent, we currently model the
preconditions of front(), back(), and operator[] as if they were
mandates, by using a static_assert to verify that extent != 0. This
causes us to incorrectly reject valid programs that instantiate these
member functions but never call them.
libstdc++-v3/ChangeLog:
* include/std/span (span::front): Remove static_assert.
(span::back): Likewise.
(span::operator[]): Likewise.
* testsuite/23_containers/span/back_neg.cc: Remove.
* testsuite/23_containers/span/front_neg.cc: Remove.
* testsuite/23_containers/span/index_op_neg.cc: Remove.
---
libstdc++-v3/include/std/span | 3 --
.../testsuite/23_containers/span/back_neg.cc | 29 -------------------
.../testsuite/23_containers/span/front_neg.cc | 29 -------------------
.../23_containers/span/index_op_neg.cc | 29 -------------------
4 files changed, 90 deletions(-)
delete mode 100644 libstdc++-v3/testsuite/23_containers/span/back_neg.cc
delete mode 100644 libstdc++-v3/testsuite/23_containers/span/front_neg.cc
delete mode 100644 libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc
diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
index f658adb04cf..1cdc0589ddb 100644
--- a/libstdc++-v3/include/std/span
+++ b/libstdc++-v3/include/std/span
@@ -264,7 +264,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr reference
front() const noexcept
{
- static_assert(extent != 0);
__glibcxx_assert(!empty());
return *this->_M_ptr;
}
@@ -272,7 +271,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr reference
back() const noexcept
{
- static_assert(extent != 0);
__glibcxx_assert(!empty());
return *(this->_M_ptr + (size() - 1));
}
@@ -280,7 +278,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr reference
operator[](size_type __idx) const noexcept
{
- static_assert(extent != 0);
__glibcxx_assert(__idx < size());
return *(this->_M_ptr + __idx);
}
diff --git a/libstdc++-v3/testsuite/23_containers/span/back_neg.cc b/libstdc++-v3/testsuite/23_containers/span/back_neg.cc
deleted file mode 100644
index c451ed10df8..00000000000
--- a/libstdc++-v3/testsuite/23_containers/span/back_neg.cc
+++ /dev/null
@@ -1,29 +0,0 @@
-// Copyright (C) 2019-2020 Free Software Foundation, Inc.
-//
-// This file is part of the GNU ISO C++ Library. This library is free
-// software; you can redistribute it and/or modify it under the
-// terms of the GNU General Public License as published by the
-// Free Software Foundation; either version 3, or (at your option)
-// any later version.
-
-// This library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU General Public License for more details.
-
-// You should have received a copy of the GNU General Public License along
-// with this library; see the file COPYING3. If not see
-// <http://www.gnu.org/licenses/>.
-
-// { dg-options "-std=gnu++2a" }
-// { dg-do compile { target c++2a } }
-
-#include <span>
-
-void
-test01()
-{
- std::span<int, 0> s;
- s.back(); // { dg-error "here" }
-}
-// { dg-error "static assertion failed" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/23_containers/span/front_neg.cc b/libstdc++-v3/testsuite/23_containers/span/front_neg.cc
deleted file mode 100644
index 38f87aa2cd5..00000000000
--- a/libstdc++-v3/testsuite/23_containers/span/front_neg.cc
+++ /dev/null
@@ -1,29 +0,0 @@
-// Copyright (C) 2019-2020 Free Software Foundation, Inc.
-//
-// This file is part of the GNU ISO C++ Library. This library is free
-// software; you can redistribute it and/or modify it under the
-// terms of the GNU General Public License as published by the
-// Free Software Foundation; either version 3, or (at your option)
-// any later version.
-
-// This library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU General Public License for more details.
-
-// You should have received a copy of the GNU General Public License along
-// with this library; see the file COPYING3. If not see
-// <http://www.gnu.org/licenses/>.
-
-// { dg-options "-std=gnu++2a" }
-// { dg-do compile { target c++2a } }
-
-#include <span>
-
-void
-test01()
-{
- std::span<int, 0> s;
- s.front(); // { dg-error "here" }
-}
-// { dg-error "static assertion failed" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc b/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc
deleted file mode 100644
index 1e8b2d8724e..00000000000
--- a/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc
+++ /dev/null
@@ -1,29 +0,0 @@
-// Copyright (C) 2019-2020 Free Software Foundation, Inc.
-//
-// This file is part of the GNU ISO C++ Library. This library is free
-// software; you can redistribute it and/or modify it under the
-// terms of the GNU General Public License as published by the
-// Free Software Foundation; either version 3, or (at your option)
-// any later version.
-
-// This library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU General Public License for more details.
-
-// You should have received a copy of the GNU General Public License along
-// with this library; see the file COPYING3. If not see
-// <http://www.gnu.org/licenses/>.
-
-// { dg-options "-std=gnu++2a" }
-// { dg-do compile { target c++2a } }
-
-#include <span>
-
-void
-test01()
-{
- std::span<int, 0> s;
- s[99]; // { dg-error "here" }
-}
-// { dg-error "static assertion failed" "" { target *-*-* } 0 }
--
2.28.0.497.g54e85e7af1
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] libstdc++: Remove overzealous static_asserts from std::span
2020-09-21 18:45 [PATCH] libstdc++: Remove overzealous static_asserts from std::span Patrick Palka
@ 2020-09-21 19:07 ` Patrick Palka
2020-09-21 21:17 ` Jonathan Wakely
0 siblings, 1 reply; 3+ messages in thread
From: Patrick Palka @ 2020-09-21 19:07 UTC (permalink / raw)
To: Patrick Palka; +Cc: gcc-patches, libstdc++
On Mon, 21 Sep 2020, Patrick Palka wrote:
> For a span with empty static extent, we currently model the
> preconditions of front(), back(), and operator[] as if they were
> mandates, by using a static_assert to verify that extent != 0. This
> causes us to incorrectly reject valid programs that instantiate these
> member functions but never call them.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/span (span::front): Remove static_assert.
> (span::back): Likewise.
> (span::operator[]): Likewise.
> * testsuite/23_containers/span/back_neg.cc: Remove.
> * testsuite/23_containers/span/front_neg.cc: Remove.
> * testsuite/23_containers/span/index_op_neg.cc: Remove.
Here's a version that rewrites rather than removes the testcases:
-- >8 --
Subject: [PATCH] libstdc++: Remove overzealous static_asserts from std::span
For a span with empty static extent, we currently model the
preconditions of front(), back(), and operator[] as if they were
mandates, by using a static_assert to verify that extent != 0. This
causes us to incorrectly reject valid programs that instantiate these
member functions but would never call them at runtime.
libstdc++-v3/ChangeLog:
* include/std/span (span::front): Remove static_assert.
(span::back): Likewise.
(span::operator[]): Likewise.
* testsuite/23_containers/span/back_neg.cc: Rewrite to verify
that we check the preconditions of back() only when it's called.
* testsuite/23_containers/span/front_neg.cc: Likewise for
front().
* testsuite/23_containers/span/index_op_neg.cc: Likewise for
operator[].
---
libstdc++-v3/include/std/span | 3 ---
.../testsuite/23_containers/span/back_neg.cc | 14 ++++++++++----
.../testsuite/23_containers/span/front_neg.cc | 14 ++++++++++----
.../testsuite/23_containers/span/index_op_neg.cc | 14 ++++++++++----
4 files changed, 30 insertions(+), 15 deletions(-)
diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
index f658adb04cf..1cdc0589ddb 100644
--- a/libstdc++-v3/include/std/span
+++ b/libstdc++-v3/include/std/span
@@ -264,7 +264,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr reference
front() const noexcept
{
- static_assert(extent != 0);
__glibcxx_assert(!empty());
return *this->_M_ptr;
}
@@ -272,7 +271,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr reference
back() const noexcept
{
- static_assert(extent != 0);
__glibcxx_assert(!empty());
return *(this->_M_ptr + (size() - 1));
}
@@ -280,7 +278,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr reference
operator[](size_type __idx) const noexcept
{
- static_assert(extent != 0);
__glibcxx_assert(__idx < size());
return *(this->_M_ptr + __idx);
}
diff --git a/libstdc++-v3/testsuite/23_containers/span/back_neg.cc b/libstdc++-v3/testsuite/23_containers/span/back_neg.cc
index c451ed10df8..f777edfa20c 100644
--- a/libstdc++-v3/testsuite/23_containers/span/back_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/span/back_neg.cc
@@ -20,10 +20,16 @@
#include <span>
-void
-test01()
+constexpr bool
+test01(bool b)
{
std::span<int, 0> s;
- s.back(); // { dg-error "here" }
+ if (b || !s.empty())
+ s.back();
+ return true;
}
-// { dg-error "static assertion failed" "" { target *-*-* } 0 }
+
+static_assert(test01(false));
+static_assert(test01(true)); // { dg-error "non-constant" }
+// { dg-error "assert" "" { target *-*-* } 0 }
+// { dg-prune-output "in 'constexpr' expansion" }
diff --git a/libstdc++-v3/testsuite/23_containers/span/front_neg.cc b/libstdc++-v3/testsuite/23_containers/span/front_neg.cc
index 38f87aa2cd5..14e5bc1e100 100644
--- a/libstdc++-v3/testsuite/23_containers/span/front_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/span/front_neg.cc
@@ -20,10 +20,16 @@
#include <span>
-void
-test01()
+constexpr bool
+test01(bool b)
{
std::span<int, 0> s;
- s.front(); // { dg-error "here" }
+ if (b || !s.empty())
+ s.front();
+ return true;
}
-// { dg-error "static assertion failed" "" { target *-*-* } 0 }
+
+static_assert(test01(false));
+static_assert(test01(true)); // { dg-error "non-constant" }
+// { dg-error "assert" "" { target *-*-* } 0 }
+// { dg-prune-output "in 'constexpr' expansion" }
diff --git a/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc b/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc
index 1e8b2d8724e..6a3bb8834b4 100644
--- a/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc
@@ -20,10 +20,16 @@
#include <span>
-void
-test01()
+constexpr bool
+test01(bool b)
{
std::span<int, 0> s;
- s[99]; // { dg-error "here" }
+ if (b || !s.empty())
+ s[99];
+ return true;
}
-// { dg-error "static assertion failed" "" { target *-*-* } 0 }
+
+static_assert(test01(false));
+static_assert(test01(true)); // { dg-error "non-constant" }
+// { dg-error "assert" "" { target *-*-* } 0 }
+// { dg-prune-output "in 'constexpr' expansion" }
--
2.28.0.497.g54e85e7af1
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] libstdc++: Remove overzealous static_asserts from std::span
2020-09-21 19:07 ` Patrick Palka
@ 2020-09-21 21:17 ` Jonathan Wakely
0 siblings, 0 replies; 3+ messages in thread
From: Jonathan Wakely @ 2020-09-21 21:17 UTC (permalink / raw)
To: Patrick Palka; +Cc: libstdc++, gcc-patches
On 21/09/20 15:07 -0400, Patrick Palka via Libstdc++ wrote:
>On Mon, 21 Sep 2020, Patrick Palka wrote:
>
>> For a span with empty static extent, we currently model the
>> preconditions of front(), back(), and operator[] as if they were
>> mandates, by using a static_assert to verify that extent != 0. This
>> causes us to incorrectly reject valid programs that instantiate these
>> member functions but never call them.
>>
>> libstdc++-v3/ChangeLog:
>>
>> * include/std/span (span::front): Remove static_assert.
>> (span::back): Likewise.
>> (span::operator[]): Likewise.
>> * testsuite/23_containers/span/back_neg.cc: Remove.
>> * testsuite/23_containers/span/front_neg.cc: Remove.
>> * testsuite/23_containers/span/index_op_neg.cc: Remove.
>
>Here's a version that rewrites rather than removes the testcases:
OK fortrunk, thanks.
We might want to backport this too.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-09-21 18:45 [PATCH] libstdc++: Remove overzealous static_asserts from std::span Patrick Palka
2020-09-21 19:07 ` Patrick Palka
2020-09-21 21:17 ` Jonathan Wakely
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