Make the pretty stack trace be an opt-in, rather than opt-out, facility. Enable pretty

stack traces by default if you use PrettyStackTraceProgram, so that existing LLVM-based 
tools will continue to get it without any changes.

llvm-svn: 193971

Author: Filip Pizlo

llvm/include/llvm-c/Core.h

@@ -434,13 +434,11 @@ void LLVMInstallFatalErrorHandler(LLVMFatalErrorHandler Handler);
 void LLVMResetFatalErrorHandler(void);
 
 /**
- * Disable LLVM's built-in stack trace code. This must be called before any
- * other LLVM APIs; otherwise the results are undefined.
- *
- * FIXME: This API should be replaced by a LLVMEnablePrettyStackTrace()
- * function; the default should be that pretty stack traces are disabled.
+ * Enable LLVM's built-in stack trace code. This intercepts the OS's crash
+ * signals and prints which component of LLVM you were in at the time if the
+ * crash.
  */
-void LLVMDisablePrettyStackTrace(void);
+void LLVMEnablePrettyStackTrace(void);
 
 /**
  * @defgroup LLVMCCoreContext Contexts

llvm/include/llvm/Support/PrettyStackTrace.h

@@ -21,11 +21,7 @@
 namespace llvm {
   class raw_ostream;
 
-  /// DisablePrettyStackTrace - Set this to true to disable this module. This
-  /// might be necessary if the host application installs its own signal
-  /// handlers which conflict with the ones installed by this module.
-  /// Defaults to false.
-  extern bool DisablePrettyStackTrace;
+  void EnablePrettyStackTrace();
 
   /// PrettyStackTraceEntry - This class is used to represent a frame of the
   /// "pretty" stack trace that is dumped when a program crashes. You can define
@@ -64,7 +60,9 @@ namespace llvm {
     const char *const *ArgV;
   public:
     PrettyStackTraceProgram(int argc, const char * const*argv)
-      : ArgC(argc), ArgV(argv) {}
+      : ArgC(argc), ArgV(argv) {
+      EnablePrettyStackTrace();
+    }
     virtual void print(raw_ostream &OS) const LLVM_OVERRIDE;
   };
 

llvm/lib/Support/PrettyStackTrace.cpp

@@ -28,10 +28,6 @@
 
 using namespace llvm;
 
-namespace llvm {
-  bool DisablePrettyStackTrace = false;
-}
-
 static ManagedStatic<sys::ThreadLocal<const PrettyStackTraceEntry> > PrettyStackTraceHead;
 
 static unsigned PrintStack(const PrettyStackTraceEntry *Entry, raw_ostream &OS){
@@ -103,17 +99,7 @@ static void CrashHandler(void *) {
 #endif
 }
 
-static bool RegisterCrashPrinter() {
-  if (!DisablePrettyStackTrace)
-    sys::AddSignalHandler(CrashHandler, 0);
-  return false;
-}
-
 PrettyStackTraceEntry::PrettyStackTraceEntry() {
-  // The first time this is called, we register the crash printer.
-  static bool HandlerRegistered = RegisterCrashPrinter();
-  (void)HandlerRegistered;
-    
   // Link ourselves.
   NextEntry = PrettyStackTraceHead->get();
   PrettyStackTraceHead->set(this);
@@ -149,6 +135,17 @@ void PrettyStackTraceProgram::print(raw_ostream &OS) const {
   OS << '\n';
 }
 
-void LLVMDisablePrettyStackTrace() {
-  DisablePrettyStackTrace = true;
+static bool RegisterCrashPrinter() {
+  sys::AddSignalHandler(CrashHandler, 0);
+  return false;
+}
+
+void llvm::EnablePrettyStackTrace() {
+  // The first time this is called, we register the crash printer.
+  static bool HandlerRegistered = RegisterCrashPrinter();
+  (void)HandlerRegistered;
+}
+
+void LLVMEnablePrettyStackTrace() {
+  EnablePrettyStackTrace();
 }