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[tsan] On OS X, optimize main thread’s ThreadState accesses 

This is a very simple optimization that gets about 10% speedup for certain programs. We’re currently storing the pointer to the main thread’s ThreadState, but we can store the state directly in a static variable, which avoid the load acquire.

Differential Revision: http://reviews.llvm.org/D20910

llvm-svn: 271906
This commit is contained in:
Kuba Brecka 2016-06-06 16:27:38 +00:00
parent 2e26d9faac
commit cdf3492191
1 changed files with 5 additions and 7 deletions
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12
compiler-rt/lib/tsan/rtl/tsan_platform_mac.cc
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@ -67,20 +67,18 @@ static void *SignalSafeGetOrAllocate(uptr *dst, uptr size) {
// when TLVs are not accessible (early process startup, thread cleanup, ...).
// The following provides a "poor man's TLV" implementation, where we use the
// shadow memory of the pointer returned by pthread_self() to store a pointer to
// the ThreadState object. The main thread's ThreadState pointer is stored
// separately in a static variable, because we need to access it even before the
// the ThreadState object. The main thread's ThreadState is stored separately
// in a static variable, because we need to access it even before the
// shadow memory is set up.
static uptr main_thread_identity = 0;
static ThreadState *main_thread_state = nullptr;
ALIGNED(64) static char main_thread_state[sizeof(ThreadState)];
ThreadState *cur_thread() {
ThreadState **fake_tls;
uptr thread_identity = (uptr)pthread_self();
if (thread_identity == main_thread_identity || main_thread_identity == 0) {
fake_tls = &main_thread_state;
} else {
fake_tls = (ThreadState **)MemToShadow(thread_identity);
return (ThreadState *)&main_thread_state;
}
ThreadState **fake_tls = (ThreadState **)MemToShadow(thread_identity);
ThreadState *thr = (ThreadState *)SignalSafeGetOrAllocate(
(uptr *)fake_tls, sizeof(ThreadState));
return thr;