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qalgorithms.h: fix mistake that MSVC has constexpr bitops in C++17 mode

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<bit> exists in C++20 and is properly both constexpr and optimized. But
in C++17 mode, we don't have constexpr bitops and instead elect to have
performance at runtime instead. But somewhere along the line, either
when they were added, when C++20 <bit> support was, or in any of the
bugfixes for other compilers, the nesting of #ifdef got messed up and we
declared that we had constexpr builtins for MSVC in C++17 too.

The macro QT_HAS_CONSTEXPR_BUILTINS isn't supposed to be used by anyone
else... but we ended up not being able to use it ourselves either. So
I'm renaming it to a more precise label.

Change-Id: I9671dee8ceb64aa9b9cafffd1741b9b4060c9753
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
(cherry picked from commit e69d80e14d24001f93442ab59b8babb7e9df0092)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Thiago Macieira 2023-02-07 18:51:59 -08:00 committed by Qt Cherry-pick Bot
parent f59731b4fb
commit e736818cef
2 changed files with 6 additions and 17 deletions
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21
src/corelib/tools/qalgorithms.h
View File

@ -41,19 +41,11 @@ inline void qDeleteAll(const Container &c)
*/
namespace QAlgorithmsPrivate {
#ifdef Q_CC_CLANG
// Clang had a bug where __builtin_ctz/clz/popcount were not marked as constexpr.
# if (defined __apple_build_version__ && __clang_major__ >= 7) || (Q_CC_CLANG >= 307)
# define QT_HAS_CONSTEXPR_BUILTINS
# endif
#elif defined(Q_CC_MSVC) && !defined(Q_PROCESSOR_ARM)
# define QT_HAS_CONSTEXPR_BUILTINS
#if defined(__cpp_lib_bitops) && __cpp_lib_bitops >= 201907L
// We use C++20 <bit> operations instead which ensures constexpr bit ops
# define QT_HAS_CONSTEXPR_BITOPS
#elif defined(Q_CC_GNU)
# define QT_HAS_CONSTEXPR_BUILTINS
#endif
#if defined QT_HAS_CONSTEXPR_BUILTINS
#if defined(Q_CC_GNU) || defined(Q_CC_CLANG)
# define QT_HAS_CONSTEXPR_BITOPS
# define QT_HAS_BUILTIN_CTZS
constexpr Q_ALWAYS_INLINE uint qt_builtin_ctzs(quint16 v) noexcept
{
@ -169,9 +161,7 @@ Q_ALWAYS_INLINE uint qt_builtin_clzs(quint16 v) noexcept
// architecture), but unlike the other compilers, MSVC has no option
// to generate code for those processors.
// So it's an acceptable compromise.
#if defined(__cpp_lib_bitops) && __cpp_lib_bitops >= 201907L
// We use C++20 <bit> operations instead which ensures constexpr popcount
#elif defined(__AVX__) || defined(__SSE4_2__) || defined(__POPCNT__)
#if defined(__AVX__) || defined(__SSE4_2__) || defined(__POPCNT__)
#define QT_POPCOUNT_CONSTEXPR
#define QT_POPCOUNT_RELAXED_CONSTEXPR
#define QALGORITHMS_USE_BUILTIN_POPCOUNT
@ -200,7 +190,6 @@ Q_ALWAYS_INLINE uint qt_builtin_popcountll(quint64 v) noexcept
#endif // __AVX__ || __SSE4_2__ || __POPCNT__
#endif // MSVC
#endif // QT_HAS_CONSTEXPR_BUILTINS
#ifndef QT_POPCOUNT_CONSTEXPR
#define QT_POPCOUNT_CONSTEXPR constexpr

2
tests/auto/widgets/kernel/qsizepolicy/tst_qsizepolicy.cpp
View File

@ -95,7 +95,7 @@ void tst_QSizePolicy::constExpr()
{
// QTBUG-69983: For ControlType != QSizePolicy::DefaultType, qCountTrailingZeroBits()
// is used, which MSVC 15.8.1 does not consider constexpr due to built-ins
# if defined(QT_HAS_CONSTEXPR_BUILTINS) && (!defined(Q_CC_MSVC) || _MSC_VER < 1915)
# if defined(QT_HAS_CONSTEXPR_BITOPS)
constexpr auto sp = QSizePolicy(QSizePolicy::Minimum, QSizePolicy::Fixed, QSizePolicy::CheckBox);
# else
constexpr auto sp = QSizePolicy(QSizePolicy::Minimum, QSizePolicy::Expanding, QSizePolicy::DefaultType);