1 files changed, 29 insertions, 21 deletions

diff --git a/lib/Support/PrettyStackTrace.cpp b/lib/Support/PrettyStackTrace.cpp
index 987778a..f9f8cab 100644
--- a/lib/Support/PrettyStackTrace.cpp
+++ b/lib/Support/PrettyStackTrace.cpp
@@ -16,9 +16,8 @@
 #include "llvm-c/Core.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Config/config.h"     // Get autoconf configuration settings
-#include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/Compiler.h"
 #include "llvm/Support/Signals.h"
-#include "llvm/Support/ThreadLocal.h"
 #include "llvm/Support/Watchdog.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -28,7 +27,17 @@
 
 using namespace llvm;
 
-static ManagedStatic<sys::ThreadLocal<const PrettyStackTraceEntry> > PrettyStackTraceHead;
+// If backtrace support is not enabled, compile out support for pretty stack
+// traces.  This has the secondary effect of not requiring thread local storage
+// when backtrace support is disabled.
+#if defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
+
+// We need a thread local pointer to manage the stack of our stack trace
+// objects, but we *really* cannot tolerate destructors running and do not want
+// to pay any overhead of synchronizing. As a consequence, we use a raw
+// thread-local variable.
+static LLVM_THREAD_LOCAL const PrettyStackTraceEntry *PrettyStackTraceHead =
+    nullptr;
 
 static unsigned PrintStack(const PrettyStackTraceEntry *Entry, raw_ostream &OS){
   unsigned NextID = 0;
@@ -46,12 +55,12 @@ static unsigned PrintStack(const PrettyStackTraceEntry *Entry, raw_ostream &OS){
 /// PrintCurStackTrace - Print the current stack trace to the specified stream.
 static void PrintCurStackTrace(raw_ostream &OS) {
   // Don't print an empty trace.
-  if (!PrettyStackTraceHead->get()) return;
+  if (!PrettyStackTraceHead) return;
   
   // If there are pretty stack frames registered, walk and emit them.
   OS << "Stack dump:\n";
   
-  PrintStack(PrettyStackTraceHead->get(), OS);
+  PrintStack(PrettyStackTraceHead, OS);
   OS.flush();
 }
 
@@ -99,28 +108,23 @@ static void CrashHandler(void *) {
 #endif
 }
 
+// defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
+#endif
+
 PrettyStackTraceEntry::PrettyStackTraceEntry() {
+#if defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
   // Link ourselves.
-  NextEntry = PrettyStackTraceHead->get();
-  PrettyStackTraceHead->set(this);
+  NextEntry = PrettyStackTraceHead;
+  PrettyStackTraceHead = this;
+#endif
 }
 
 PrettyStackTraceEntry::~PrettyStackTraceEntry() {
-  // Do nothing if PrettyStackTraceHead is uninitialized. This can only happen
-  // if a shutdown occurred after we created the PrettyStackTraceEntry. That
-  // does occur in the following idiom:
-  //
-  // PrettyStackTraceProgram X(...);
-  // llvm_shutdown_obj Y;
-  //
-  // Without this check, we may end up removing ourselves from the stack trace
-  // after PrettyStackTraceHead has already been destroyed.
-  if (!PrettyStackTraceHead.isConstructed())
-    return;
-  
-  assert(PrettyStackTraceHead->get() == this &&
+#if defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
+  assert(PrettyStackTraceHead == this &&
          "Pretty stack trace entry destruction is out of order");
-  PrettyStackTraceHead->set(getNextEntry());
+  PrettyStackTraceHead = getNextEntry();
+#endif
 }
 
 void PrettyStackTraceString::print(raw_ostream &OS) const {
@@ -135,15 +139,19 @@ void PrettyStackTraceProgram::print(raw_ostream &OS) const {
   OS << '\n';
 }
 
+#if defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
 static bool RegisterCrashPrinter() {
   sys::AddSignalHandler(CrashHandler, nullptr);
   return false;
 }
+#endif
 
 void llvm::EnablePrettyStackTrace() {
+#if defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
   // The first time this is called, we register the crash printer.
   static bool HandlerRegistered = RegisterCrashPrinter();
   (void)HandlerRegistered;
+#endif
 }
 
 void LLVMEnablePrettyStackTrace() {