Bigcheese added a comment.
This looks like a good simplification, but I think `call_once` could be
simplified more.
================
Comment at: llvm/cmake/modules/CheckAtomic.cmake:46
+ if (NOT HAVE_ATOMICS_WITH_LIB)
+ message(FATAL_ERROR "Host compiler must support atomic!")
endif()
----------------
Indentation?
================
Comment at: llvm/cmake/modules/CheckAtomic.cmake:75
-## TODO: This define is only used for the legacy atomic operations in
-## llvm's Atomic.h, which should be replaced. Other code simply
-## assumes C++11 <atomic> works.
-CHECK_CXX_SOURCE_COMPILES("
-#ifdef _MSC_VER
-#include <windows.h>
-#endif
-int main() {
-#ifdef _MSC_VER
- volatile LONG val = 1;
- MemoryBarrier();
- InterlockedCompareExchange(&val, 0, 1);
- InterlockedIncrement(&val);
- InterlockedDecrement(&val);
-#else
- volatile unsigned long val = 1;
- __sync_synchronize();
- __sync_val_compare_and_swap(&val, 1, 0);
- __sync_add_and_fetch(&val, 1);
- __sync_sub_and_fetch(&val, 1);
-#endif
- return 0;
- }
-" LLVM_HAS_ATOMICS)
-
if( NOT LLVM_HAS_ATOMICS )
message(STATUS "Warning: LLVM will be built thread-unsafe because atomic
builtins are missing")
----------------
Does anything else set `LLVM_HAS_ATOMICS`?
================
Comment at: llvm/include/llvm/Support/Threading.h:111
+ std::atomic_thread_fence(std::memory_order_seq_cst);
TsanIgnoreWritesBegin();
TsanHappensBefore(&flag.status);
----------------
Not sure we still need the tsan hooks when using `std::atomic`.
================
Comment at: llvm/include/llvm/Support/Threading.h:118
+ InitStatus tmp = flag.status;
+ std::atomic_thread_fence(std::memory_order_seq_cst);
while (tmp != Done) {
----------------
Do we actually need thread fences here?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D65493/new/
https://reviews.llvm.org/D65493
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