qsimd_p.h: Restore compatibility with C code

The qCpuHasFeature() macro doesn't work in C mode in x86 because it
tries to use enums only available in C++ mode, but the qCpuFeatures()
function does. You can write:

  if ((qCompilerCpuFeatures & cpu_feature_avx2) ||
      (qCpuFeatures() & cpu_feature_avx2))

In C code and this will compile.

Change-Id: Ic15405335d804bdea761fffd16d50dc4f17f572e
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

2 files changed, 32 insertions, 50 deletions

diff --git a/src/corelib/global/qsimd.cpp b/src/corelib/global/qsimd.cpp
index 72fcf63094..d2a0686097 100644
--- a/src/corelib/global/qsimd.cpp
+++ b/src/corelib/global/qsimd.cpp
@@ -584,10 +584,10 @@ static inline uint detectProcessorFeatures()
 static const quint64 minFeature = qCompilerCpuFeatures;
 
 static constexpr auto SimdInitialized = QCpuFeatureType(1) << (sizeof(QCpuFeatureType) * 8 - 1);
-QBasicAtomicInteger<QCpuFeatureType> qt_cpu_features[1] = { 0 };
+Q_ATOMIC(QCpuFeatureType) QT_MANGLE_NAMESPACE(qt_cpu_features)[1] = { 0 };
 
 QT_FUNCTION_TARGET_BASELINE
-quint64 qDetectCpuFeatures()
+uint64_t QT_MANGLE_NAMESPACE(qDetectCpuFeatures)()
 {
     auto minFeatureTest = minFeature;
 #if defined(Q_OS_LINUX) && defined(Q_PROCESSOR_ARM_64)
@@ -595,7 +595,7 @@ quint64 qDetectCpuFeatures()
     // automatically by compilers, we can just add runtime check.
     minFeatureTest &= ~(CpuFeatureAES|CpuFeatureCRC32);
 #endif
-    quint64 f = detectProcessorFeatures();
+    QCpuFeatureType f = detectProcessorFeatures();
 
     // Intentionally NOT qgetenv (this code runs too early)
     if (char *disable = getenv("QT_NO_CPU_FEATURE"); disable && *disable) {
@@ -632,7 +632,8 @@ quint64 qDetectCpuFeatures()
     }
 
     assert((f & SimdInitialized) == 0);
-    qt_cpu_features[0].storeRelease(f | SimdInitialized);
+    f |= SimdInitialized;
+    std::atomic_store_explicit(QT_MANGLE_NAMESPACE(qt_cpu_features), f, std::memory_order_relaxed);
     return f;
 }
 
@@ -791,7 +792,7 @@ static bool checkRdrndWorks() noexcept { return false; }
 namespace {
 struct QSimdInitializer
 {
-    inline QSimdInitializer() { qDetectCpuFeatures(); }
+    inline QSimdInitializer() { QT_MANGLE_NAMESPACE(qDetectCpuFeatures)(); }
 };
 }
 
diff --git a/src/corelib/global/qsimd_p.h b/src/corelib/global/qsimd_p.h
index ad769ee7a6..ccb995588b 100644
--- a/src/corelib/global/qsimd_p.h
+++ b/src/corelib/global/qsimd_p.h
@@ -1,7 +1,7 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
-** Copyright (C) 2018 Intel Corporation.
+** Copyright (C) 2021 The Qt Company Ltd.
+** Copyright (C) 2022 Intel Corporation.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -253,28 +253,6 @@ asm(
     defined(__FMA__) && defined(__LZCNT__) && defined(__RDRND__)
 #    define __haswell__       1
 #  endif
-
-QT_BEGIN_NAMESPACE
-static const quint64 qCompilerCpuFeatures = _compilerCpuFeatures;
-
-// This constant does not include all CPU features found in a Haswell, only
-// those that we'd have optimized code for.
-// Note: must use Q_CONSTEXPR here, as this file may be compiled in C mode.
-static const quint64 CpuFeatureArchHaswell    = 0
-        | CpuFeatureSSE2
-        | CpuFeatureSSE3
-        | CpuFeatureSSSE3
-        | CpuFeatureSSE4_1
-        | CpuFeatureSSE4_2
-        | CpuFeatureFMA
-        | CpuFeaturePOPCNT
-        | CpuFeatureAVX
-        | CpuFeatureF16C
-        | CpuFeatureAVX2
-        | CpuFeatureBMI
-        | CpuFeatureBMI2;
-QT_END_NAMESPACE
-
 #endif  /* Q_PROCESSOR_X86 */
 
 // NEON intrinsics
@@ -329,12 +307,6 @@ inline uint8_t vaddv_u8(uint8x8_t v8)
 #endif
 #endif
 
-
-#ifdef __cplusplus
-#include <qatomic.h>
-
-QT_BEGIN_NAMESPACE
-
 #ifndef Q_PROCESSOR_X86
 enum CPUFeatures {
 #if defined(Q_PROCESSOR_ARM)
@@ -368,29 +340,35 @@ static const quint64 qCompilerCpuFeatures = 0
         ;
 #endif
 
-#ifdef Q_PROCESSOR_X86
-using QCpuFeatureType = quint64;
+#ifdef __cplusplus
+#  include <atomic>
+#  define Q_ATOMIC(T)   std::atomic<T>
+QT_BEGIN_NAMESPACE
+using std::atomic_load_explicit;
+static constexpr auto memory_order_relaxed = std::memory_order_relaxed;
+extern "C" {
 #else
-using QCpuFeatureType = unsigned;
+#  include <stdatomic.h>
+#  include <stdbool.h>
+#  define Q_ATOMIC(T)   _Atomic(T)
 #endif
-extern Q_CORE_EXPORT QBasicAtomicInteger<QCpuFeatureType> qt_cpu_features[1];
-Q_CORE_EXPORT quint64 qDetectCpuFeatures();
 
-#if defined(Q_PROCESSOR_X86) && QT_COMPILER_SUPPORTS_HERE(RDRND) && !defined(QT_BOOTSTRAPPED)
-Q_CORE_EXPORT qsizetype qRandomCpu(void *, qsizetype) noexcept;
+#ifdef Q_PROCESSOR_X86
+typedef uint64_t QCpuFeatureType;
+static const QCpuFeatureType qCompilerCpuFeatures = _compilerCpuFeatures;
+static const QCpuFeatureType CpuFeatureArchHaswell = cpu_haswell;
 #else
-static inline qsizetype qRandomCpu(void *, qsizetype) noexcept
-{
-    return 0;
-}
+typedef unsigned QCpuFeatureType;
 #endif
+extern Q_CORE_EXPORT Q_ATOMIC(QCpuFeatureType) QT_MANGLE_NAMESPACE(qt_cpu_features)[1];
+Q_CORE_EXPORT uint64_t QT_MANGLE_NAMESPACE(qDetectCpuFeatures)();
 
-static inline quint64 qCpuFeatures()
+static inline uint64_t qCpuFeatures()
 {
-    quint64 features = qt_cpu_features[0].loadRelaxed();
-    if constexpr (!QT_SUPPORTS_INIT_PRIORITY) {
+    quint64 features = atomic_load_explicit(QT_MANGLE_NAMESPACE(qt_cpu_features), memory_order_relaxed);
+    if (!QT_SUPPORTS_INIT_PRIORITY) {
         if (Q_UNLIKELY(features == 0))
-            features = qDetectCpuFeatures();
+            features = QT_MANGLE_NAMESPACE(qDetectCpuFeatures)();
     }
     return features;
 }
@@ -398,6 +376,9 @@ static inline quint64 qCpuFeatures()
 #define qCpuHasFeature(feature)     (((qCompilerCpuFeatures & CpuFeature ## feature) == CpuFeature ## feature) \
                                      || ((qCpuFeatures() & CpuFeature ## feature) == CpuFeature ## feature))
 
+#ifdef __cplusplus
+} // extern "C"
+
 #  if defined(Q_PROCESSOR_X86) && QT_COMPILER_SUPPORTS_HERE(RDRND) && !defined(QT_BOOTSTRAPPED)
 Q_CORE_EXPORT qsizetype qRandomCpu(void *, qsizetype) noexcept;