[libc++] Optimize std::exception_ptr
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,48 @@ | ||
| // -*- C++ -*- | ||
| //===----------------------------------------------------------------------===// | ||
| // | ||
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. | ||
| // See https://llvm.org/LICENSE.txt for license information. | ||
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| namespace __cxxabiv1 { | ||
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| extern "C" { | ||
| _LIBCPP_OVERRIDABLE_FUNC_VIS void __cxa_increment_exception_refcount(void*) _NOEXCEPT; | ||
| _LIBCPP_OVERRIDABLE_FUNC_VIS void __cxa_decrement_exception_refcount(void*) _NOEXCEPT; | ||
| _LIBCPP_OVERRIDABLE_FUNC_VIS void* __cxa_current_primary_exception() _NOEXCEPT; | ||
| _LIBCPP_OVERRIDABLE_FUNC_VIS void __cxa_rethrow_primary_exception(void*); | ||
| } | ||
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| } // namespace __cxxabiv1 | ||
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| namespace std { | ||
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| _LIBCPP_HIDE_FROM_ABI _LIBCPP_ALWAYS_INLINE inline void exception_ptr::__increment_refcount(void* __ptr) _NOEXCEPT { | ||
|
There was a problem hiding this comment. Please don't spray always_inline everywhere. There was a problem hiding this comment. I only added it to That being said, I guess I was overly careful here. I will remove it |
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| if (__ptr) | ||
| __cxxabiv1::__cxa_increment_exception_refcount(__ptr); | ||
| } | ||
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| _LIBCPP_HIDE_FROM_ABI _LIBCPP_ALWAYS_INLINE inline void exception_ptr::__decrement_refcount(void* __ptr) _NOEXCEPT { | ||
| if (__ptr) | ||
| __cxxabiv1::__cxa_decrement_exception_refcount(__ptr); | ||
| } | ||
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| _LIBCPP_EXPORTED_FROM_LIB_INLINEABLE exception_ptr current_exception() _NOEXCEPT { | ||
| // It would be nicer if there was a constructor that took a ptr, then | ||
| // this whole function would be just: | ||
| // return exception_ptr(__cxa_current_primary_exception()); | ||
| exception_ptr __ptr; | ||
| __ptr.__ptr_ = __cxxabiv1::__cxa_current_primary_exception(); | ||
| return __ptr; | ||
| } | ||
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| _LIBCPP_EXPORTED_FROM_LIB_INLINEABLE void rethrow_exception(exception_ptr __ptr) { | ||
| __cxxabiv1::__cxa_rethrow_primary_exception(__ptr.__ptr_); | ||
| // if __ptr.__ptr_ is NULL, above returns so we terminate. | ||
| _LIBCPP_VERBOSE_ABORT("tried to rethrow an empty exception_ptr\n"); | ||
| } | ||
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| } // namespace std | ||
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I'm not convinced this new macro is necessary. IIUC these functions are supposed to be inlined, so there isn't much point in providing an external version (except for ABI of course, but we don't need to use the dylib functions).
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Full disclosure: This isn't actually my idea. It was yours (modulo potential misunderstandings on my side). It was originally proposed back in April 2022 in https://reviews.llvm.org/D122536. Happy to adjust it however you prefer
correct
How should we ensure that the functions are still emitted as part of the dylib? Currently I rely on
_LIBCPP_EXPORTED_FROM_LIB_INLINEABLEto be markedinlinein the headers but as non-inline in the dylib. By marking it non-inline in the dylib, I ensure that the compiler actually emits code for it. If I would mark theminlinealso in the dylib, the compiler wouldn't actually emit any code, since the functions are never called / instantiated by the dylibRight, I think we can let the compiler choose freely to either use the inlined or the dylib-provided version. This means we might not need
[[gnu::inline]]/__attribute__((__gnu_inline__)).I used it primarily because you proposed its usage back in April 2022 in https://reviews.llvm.org/D122536. It provides a slight benefit that the linker has less work to do (it doesn't have to discard many duplicated definitions of the same inline function). Not sure if we consider this to be worth it, though 🤷