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| author | Jonathan Wakely <jwakely@redhat.com> | 2023-05-25 09:57:46 +0100 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2023-05-31 21:01:15 +0100 |
| commit | fb409a15d9babc78fe1d9957afcbaf1102cce58f (patch) | |
| tree | b597fb9c7e3211c9099661a94a765f54b4cb9f9c /libstdc++-v3 | |
| parent | a239a35075ffd8b34f1db72c22998a625ff962b5 (diff) | |
| download | gcc-fb409a15d9babc78fe1d9957afcbaf1102cce58f.zip gcc-fb409a15d9babc78fe1d9957afcbaf1102cce58f.tar.gz gcc-fb409a15d9babc78fe1d9957afcbaf1102cce58f.tar.bz2 | |
libstdc++: Express std::vector's size() <= capacity() invariant in code
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).
Diffstat (limited to 'libstdc++-v3')
| -rw-r--r-- | libstdc++-v3/include/bits/stl_vector.h | 30 | ||||
| -rw-r--r-- | libstdc++-v3/testsuite/23_containers/vector/capacity/invariant.cc | 16 | ||||
| -rw-r--r-- | libstdc++-v3/testsuite/23_containers/vector/types/1.cc | 2 |
3 files changed, 44 insertions, 4 deletions
diff --git a/libstdc++-v3/include/bits/stl_vector.h b/libstdc++-v3/include/bits/stl_vector.h index acb2939..e593be4 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 0000000..d68db69 --- /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 079e5af..9be07d9 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> |