Tested x86_64-linux. Pushed to trunk.
-- >8 --
This adds optimizer hints so that GCC knows that size() <= capacity() is
always true. This allows the compiler to optimize away re-allocating
paths when assigning new values to the vector without resizing it, e.g.,
vec.assign(vec.size(), new_val).
libstdc++-v3/ChangeLog:
* include/bits/stl_vector.h (_Vector_base::_M_invariant()): New
function.
(vector::size(), vector::capacity()): Call _M_invariant().
* testsuite/23_containers/vector/capacity/invariant.cc: New test.
* testsuite/23_containers/vector/types/1.cc: Add suppression for
false positive warning (PR110060).
---
libstdc++-v3/include/bits/stl_vector.h | 30 +++++++++++++++++--
.../vector/capacity/invariant.cc | 16 ++++++++++
.../testsuite/23_containers/vector/types/1.cc | 2 +-
3 files changed, 44 insertions(+), 4 deletions(-)
create mode 100644
libstdc++-v3/testsuite/23_containers/vector/capacity/invariant.cc
diff --git a/libstdc++-v3/include/bits/stl_vector.h
b/libstdc++-v3/include/bits/stl_vector.h
index acb29396d26..e593be443bc 100644
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -388,6 +388,24 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
}
protected:
+
+ __attribute__((__always_inline__))
+ _GLIBCXX20_CONSTEXPR void
+ _M_invariant() const
+ {
+#if __OPTIMIZE__
+ if (this->_M_impl._M_finish < this->_M_impl._M_start)
+ __builtin_unreachable();
+ if (this->_M_impl._M_finish > this->_M_impl._M_end_of_storage)
+ __builtin_unreachable();
+
+ size_t __sz = this->_M_impl._M_finish - this->_M_impl._M_start;
+ size_t __cap = this->_M_impl._M_end_of_storage - this->_M_impl._M_start;
+ if (__sz > __cap)
+ __builtin_unreachable();
+#endif
+ }
+
_GLIBCXX20_CONSTEXPR
void
_M_create_storage(size_t __n)
@@ -987,7 +1005,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
size_type
size() const _GLIBCXX_NOEXCEPT
- { return size_type(this->_M_impl._M_finish - this->_M_impl._M_start); }
+ {
+ _Base::_M_invariant();
+ return size_type(this->_M_impl._M_finish - this->_M_impl._M_start);
+ }
/** Returns the size() of the largest possible %vector. */
_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
@@ -1073,8 +1094,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
size_type
capacity() const _GLIBCXX_NOEXCEPT
- { return size_type(this->_M_impl._M_end_of_storage
- - this->_M_impl._M_start); }
+ {
+ _Base::_M_invariant();
+ return size_type(this->_M_impl._M_end_of_storage
+ - this->_M_impl._M_start);
+ }
/**
* Returns true if the %vector is empty. (Thus begin() would
diff --git a/libstdc++-v3/testsuite/23_containers/vector/capacity/invariant.cc
b/libstdc++-v3/testsuite/23_containers/vector/capacity/invariant.cc
new file mode 100644
index 00000000000..d68db694add
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/capacity/invariant.cc
@@ -0,0 +1,16 @@
+// { dg-do compile }
+// { dg-options "-O3 -g0" }
+// { dg-final { scan-assembler-not "_Znw" } }
+// GCC should be able to optimize away the paths involving reallocation.
+
+#include <vector>
+
+void fill(std::vector<int>& vec)
+{
+ vec.assign(vec.size(), 0);
+}
+
+void fill_val(std::vector<int>& vec, int i)
+{
+ vec.assign(vec.size(), i);
+}
diff --git a/libstdc++-v3/testsuite/23_containers/vector/types/1.cc
b/libstdc++-v3/testsuite/23_containers/vector/types/1.cc
index 079e5af9556..9be07d9fd5c 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/types/1.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/types/1.cc
@@ -18,7 +18,7 @@
// <http://www.gnu.org/licenses/>.
// { dg-do compile }
-// { dg-options "-Wno-unused-result" }
+// { dg-options "-Wno-unused-result -Wno-stringop-overread" }
#include <vector>
#include <testsuite_greedy_ops.h>
--
2.40.1
