[gcc r11-2881] libstdc++: Enable assertions in constexpr string_view members [PR 71960]

[Jonathan Wakely]

https://gcc.gnu.org/g:3eefb302d2bd8502cb3d8fe44e672b11092ccaf6

commit r11-2881-g3eefb302d2bd8502cb3d8fe44e672b11092ccaf6
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Aug 26 14:47:51 2020 +0100

    libstdc++: Enable assertions in constexpr string_view members [PR 71960]
    
    Since GCC 6.1 there is no reason we can't just use __glibcxx_assert in
    constexpr functions in string_view. As long as the condition is true,
    there will be no call to std::__replacement_assert that would make the
    function ineligible for constant evaluation.
    
            PR libstdc++/71960
            * include/experimental/string_view (basic_string_view):
            Enable debug assertions.
            * include/std/string_view (basic_string_view):
            Likewise.

Diff:
---
 libstdc++-v3/include/experimental/string_view | 9 +++------
 libstdc++-v3/include/std/string_view          | 9 +++------
 2 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/libstdc++-v3/include/experimental/string_view b/libstdc++-v3/include/experimental/string_view
index 629db577c29..5567184cf0e 100644
--- a/libstdc++-v3/include/experimental/string_view
+++ b/libstdc++-v3/include/experimental/string_view
@@ -179,8 +179,7 @@ inline namespace fundamentals_v1
       constexpr const _CharT&
       operator[](size_type __pos) const
       {
-	// TODO: Assert to restore in a way compatible with the constexpr.
-	// __glibcxx_assert(__pos < this->_M_len);
+	__glibcxx_assert(__pos < this->_M_len);
 	return *(this->_M_str + __pos);
       }
 
@@ -199,16 +198,14 @@ inline namespace fundamentals_v1
       constexpr const _CharT&
       front() const
       {
-	// TODO: Assert to restore in a way compatible with the constexpr.
-	// __glibcxx_assert(this->_M_len > 0);
+	__glibcxx_assert(this->_M_len > 0);
 	return *this->_M_str;
       }
 
       constexpr const _CharT&
       back() const
       {
-	// TODO: Assert to restore in a way compatible with the constexpr.
-	// __glibcxx_assert(this->_M_len > 0);
+	__glibcxx_assert(this->_M_len > 0);
 	return *(this->_M_str + this->_M_len - 1);
       }
 
diff --git a/libstdc++-v3/include/std/string_view b/libstdc++-v3/include/std/string_view
index ca0d6265098..f05ff32d9e5 100644
--- a/libstdc++-v3/include/std/string_view
+++ b/libstdc++-v3/include/std/string_view
@@ -207,8 +207,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       constexpr const_reference
       operator[](size_type __pos) const noexcept
       {
-	// TODO: Assert to restore in a way compatible with the constexpr.
-	// __glibcxx_assert(__pos < this->_M_len);
+	__glibcxx_assert(__pos < this->_M_len);
 	return *(this->_M_str + __pos);
       }
 
@@ -225,16 +224,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       constexpr const_reference
       front() const noexcept
       {
-	// TODO: Assert to restore in a way compatible with the constexpr.
-	// __glibcxx_assert(this->_M_len > 0);
+	__glibcxx_assert(this->_M_len > 0);
 	return *this->_M_str;
       }
 
       constexpr const_reference
       back() const noexcept
       {
-	// TODO: Assert to restore in a way compatible with the constexpr.
-	// __glibcxx_assert(this->_M_len > 0);
+	__glibcxx_assert(this->_M_len > 0);
 	return *(this->_M_str + this->_M_len - 1);
       }