[asan] Make GetFakeStackFast()/GetFakeStackFastAlways() lazily init fake_stack_tls (llvm#163481)

To simplify implementation of llvm#160135

Author: vitalybuka

compiler-rt/lib/asan/asan_fake_stack.cpp

@@ -231,17 +231,25 @@ static FakeStack* GetFakeStack() {
 }
 
 static FakeStack* GetFakeStackFast() {
-  if (FakeStack* fs = GetTLSFakeStack())
+  FakeStack* fs = GetTLSFakeStack();
+  if (LIKELY(fs))
     return fs;
   if (!__asan_option_detect_stack_use_after_return)
     return nullptr;
-  return GetFakeStack();
+  fs = GetFakeStack();
+  if (LIKELY(fs))
+    SetTLSFakeStack(fs);
+  return fs;
 }
 
 static FakeStack* GetFakeStackFastAlways() {
-  if (FakeStack* fs = GetTLSFakeStack())
+  FakeStack* fs = GetTLSFakeStack();
+  if (LIKELY(fs))
     return fs;
-  return GetFakeStack();
+  fs = GetFakeStack();
+  if (LIKELY(fs))
+    SetTLSFakeStack(fs);
+  return fs;
 }
 
 static ALWAYS_INLINE uptr OnMalloc(uptr class_id, uptr size) {

compiler-rt/lib/asan/asan_fake_stack.h

@@ -195,7 +195,7 @@ class FakeStack {
   void *true_start;
 };
 
-void SetTLSFakeStack(FakeStack *fs);
+void SetTLSFakeStack(FakeStack* fs);
 
 }  // namespace __asan