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[Runtime] Improve performance and memory footprint of compatibility o… #78818

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Jan 24, 2025
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[Runtime] Improve performance and memory footprint of compatibility o… #78818

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43 changes: 33 additions & 10 deletions stdlib/public/CompatibilityOverride/CompatibilityOverride.h
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Original file line number Diff line number Diff line change
Expand Up @@ -82,10 +82,10 @@
#define COMPATIBILITY_OVERRIDE_H

#include "../runtime/Private.h"
#include "swift/Runtime/CMakeConfig.h"
#include "swift/Runtime/Concurrency.h"
#include "swift/Runtime/Metadata.h"
#include "swift/Runtime/Once.h"
#include "swift/Runtime/CMakeConfig.h"
#include <atomic>
#include <type_traits>

namespace swift {
Expand Down Expand Up @@ -192,15 +192,38 @@ namespace swift {
/// functionality must be available as swift_funcNameHereImpl.
#define COMPATIBILITY_OVERRIDE(name, ret, attrs, ccAttrs, namespace, \
typedArgs, namedArgs) \
/* We are creating this separate function for the override case, */ \
/* to prevent a stack frame from being created for the default case. */ \
SWIFT_NOINLINE \
static ret swift_##name##Slow(COMPATIBILITY_UNPAREN_WITH_COMMA(typedArgs) \
std::atomic<uintptr_t> &Override, \
uintptr_t fn, Original_##name defaultImpl) { \
constexpr uintptr_t DEFAULT_IMPL_SENTINEL = 0x1; \
if (SWIFT_UNLIKELY(fn == 0x0)) { \
fn = (uintptr_t)getOverride_##name(); \
if (fn == 0x0) { \
Override.store(DEFAULT_IMPL_SENTINEL, \
std::memory_order::memory_order_relaxed); \
return defaultImpl COMPATIBILITY_PAREN(namedArgs); \
} \
Override.store(fn, std::memory_order::memory_order_relaxed); \
} \
return ((Override_##name)fn)(COMPATIBILITY_UNPAREN_WITH_COMMA(namedArgs) \
defaultImpl); \
} \
attrs ccAttrs ret namespace swift_##name COMPATIBILITY_PAREN(typedArgs) { \
static Override_##name Override; \
static swift_once_t Predicate; \
swift_once( \
&Predicate, [](void *) { Override = getOverride_##name(); }, nullptr); \
if (Override != nullptr) \
return Override(COMPATIBILITY_UNPAREN_WITH_COMMA(namedArgs) \
swift_##name##Impl); \
return swift_##name##Impl COMPATIBILITY_PAREN(namedArgs); \
constexpr uintptr_t DEFAULT_IMPL_SENTINEL = 0x1; \
static std::atomic<uintptr_t> Override; \
uintptr_t fn = Override.load(std::memory_order::memory_order_relaxed); \
if (SWIFT_LIKELY(fn == DEFAULT_IMPL_SENTINEL)) { \
return swift_##name##Impl COMPATIBILITY_PAREN(namedArgs); \
} else if (SWIFT_UNLIKELY(fn == 0x0)) { \
return swift_##name##Slow(COMPATIBILITY_UNPAREN_WITH_COMMA(namedArgs) \
Override, \
fn, &swift_##name##Impl); \
} \
return ((Override_##name)fn)(COMPATIBILITY_UNPAREN_WITH_COMMA(namedArgs) & \
swift_##name##Impl); \
}

#endif // #else SWIFT_STDLIB_SUPPORT_BACK_DEPLOYMENT
Expand Down