diff options
| author | Stephan Bergmann <sbergman@redhat.com> | 2019-09-25 14:43:16 +0200 |
|---|---|---|
| committer | Stephan Bergmann <sbergman@redhat.com> | 2019-09-25 20:55:53 +0200 |
| commit | 689dc632875c4ec51e44cf53718d625d9a217d9c (patch) | |
| tree | 90a01344b3a678b114a7f8038005ae75062a2e71 /config_host | |
| parent | 52b3333ff592b10b9b628863e7b06506b2106568 (diff) | |
constinit, here we come
Following up on b13421011d9377676e1adc282634991d5064a866 "better data
structures for some static const vars":
* Make the o3tl::sorted_vector ctor taking an initializer_list constexpr.
<https://wg21.link/P0202R3> "Add Constexpr Modifiers to Functions in
<algorithm> and <utility> Headers", which will be in C++2a and is already
implemented by recent libc++ and libstdc++ according to
<https://en.cppreference.com/w/cpp/compiler_support
#C.2B.2B2a_library_features>, makes std::sort constexpr but explicitly keeps
std::stable_sort non-constexpr. ("Algorithms stable_partition, inplace_merge
and stable_sort allocate memory, construct variables using placement new, use
unique_ptr and do other things not acceptable in constexpr expressions.
Making those algorithms constexpr seems to be a hard task that would require
a lot of intrinsics. Those algorithms are not marked with constexpr in this
wording.") But keep o3tl::sorted_vector::Resort (which was introduced in
c59355e936446fe55960209e543b072acb6b2170 "fdo#58793: re-implement
SwpHintsArray::Resort()") using std::stable_sort instead of std::sort, in
case that is relevant for its pre-exisiting uses.
* <https://wg21.link/P1004R2> "Making std::vector constexpr", which was voted
into C++2a according to <https://wg21.link/n4829> "Editors' Report --
Programming Languages -- C++", will make the relevant parts of std::vector
constexpr. But none of libc++, libstdc++, and MSVC implement that as of now.
* Introduce HAVE_CPP_CONSTINIT_SORTED_VECTOR to hide the constinit behind for
now for the one case from b13421011d9377676e1adc282634991d5064a866 "better
data structures for some static const vars" that can clearly be constinit
once constexpr std::vector is supported by compilers. The other three cases
(s_aContainerDocumentCommands in
chart2/source/controller/main/CommandDispatchContainer.cxx,
aMetricCompatibleMap in vcl/source/font/PhysicalFontCollection.cxx, and
aBlacklist in writerfilter/source/dmapper/PropertyMap.cxx) would each need a
constexpr OUString first. (Technically, the constinit would not even be
needed, but it nicely documents our intent that this will actually be
initialized at compile-time once compilers support that.)
Change-Id: Ibeb138f120528be3a7a09b3912143bf795fbab29
Reviewed-on: https://gerrit.libreoffice.org/79556
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Diffstat (limited to 'config_host')
| -rw-r--r-- | config_host/config_global.h.in | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/config_host/config_global.h.in b/config_host/config_global.h.in index 2e986fbe24b6..adb36c39ab8b 100644 --- a/config_host/config_global.h.in +++ b/config_host/config_global.h.in @@ -24,6 +24,11 @@ Any change in this header will cause a rebuild of almost everything. /* Guaranteed copy elision (C++17), __cpp_guaranteed_copy_elision (C++2a): */ #define HAVE_CPP_GUARANTEED_COPY_ELISION 0 +// Compiler supports all of C++2a <https://wg21.link/P0202R3> "Add Constexpr Modifiers to Functions +// in <algorithm> and <utility> Headers", <https://wg21.link/P1004R2> "Making std::vector +// constexpr", and <https://wg21.link/P1143R2> "Adding the constinit keyword": +#define HAVE_CPP_CONSTINIT_SORTED_VECTOR 0 + /* GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87150> "move ctor wrongly chosen in return stmt (derived vs. base)": */ #define HAVE_GCC_BUG_87150 0 |