make BoxedTraceback hold a single line, instead of a vector. rename...

make BoxedTraceback hold a single line, instead of a vector.  rename BoxedTraceback::Here to BoxedTraceback::here

src/codegen/unwinding.cpp

@@ -518,7 +518,7 @@ public:
             exc_info.reraise = false;
             return;
         }
-        BoxedTraceback::Here(line_info, reinterpret_cast<BoxedTraceback**>(&exc_info.traceback));
+        BoxedTraceback::here(line_info, &exc_info.traceback);
     }
 
     void logException() {
@@ -614,7 +614,7 @@ void exceptionCaughtInInterpreter(LineInfo line_info, ExcInfo* exc_info) {
         exc_info->reraise = false;
         return;
     }
-    BoxedTraceback::Here(line_info, reinterpret_cast<BoxedTraceback**>(&exc_info->traceback));
+    BoxedTraceback::here(line_info, &exc_info->traceback);
 }
 
 void unwindingThroughFrame(PythonUnwindSession* unwind_session, unw_cursor_t* cursor) {
@@ -754,18 +754,16 @@ BoxedTraceback* getTraceback() {
 
     Timer _t("getTraceback", 1000);
 
-    BoxedTraceback::LinesVector entries;
+    Box* tb = new BoxedTraceback();
     unwindPythonStack([&](PythonFrameIteratorImpl* frame_iter) {
-        entries.push_back(lineInfoForFrame(frame_iter));
+        BoxedTraceback::here(lineInfoForFrame(frame_iter), &tb);
         return false;
     });
 
-    std::reverse(entries.begin(), entries.end());
-
     long us = _t.end();
     us_gettraceback.log(us);
 
-    return new BoxedTraceback(std::move(entries));
+    return static_cast<BoxedTraceback*>(tb);
 }
 
 ExcInfo* getFrameExcInfo() {

src/runtime/stacktrace.cpp

@@ -55,8 +55,7 @@ void raiseExc(Box* exc_obj) {
 void raiseSyntaxError(const char* msg, int lineno, int col_offset, llvm::StringRef file, llvm::StringRef func) {
     Box* exc = runtimeCall(SyntaxError, ArgPassSpec(1), boxString(msg), NULL, NULL, NULL, NULL);
 
-    auto tb = new BoxedTraceback();
-    tb->addLine(LineInfo(lineno, col_offset, file, func));
+    auto tb = new BoxedTraceback(LineInfo(lineno, col_offset, file, func), None);
     throw ExcInfo(exc->cls, exc, tb);
 }
 

src/runtime/traceback.cpp

@@ -57,7 +57,7 @@ void printTraceback(Box* b) {
     fprintf(stderr, "Traceback (most recent call last):\n");
 
     for (; tb && tb != None; tb = static_cast<BoxedTraceback*>(tb->tb_next)) {
-        for (auto line : tb->lines) {
+        auto& line = tb->line;
         fprintf(stderr, "  File \"%s\", line %d, in %s:\n", line.file.c_str(), line.line, line.func.c_str());
 
         if (line.line < 0)
@@ -92,11 +92,6 @@ void printTraceback(Box* b) {
             fclose(f);
         }
     }
-    }
-}
-
-void BoxedTraceback::addLine(const LineInfo line) {
-    lines.insert(lines.begin(), line);
 }
 
 Box* BoxedTraceback::getLines(Box* b) {
@@ -107,8 +102,8 @@ Box* BoxedTraceback::getLines(Box* b) {
     if (!tb->py_lines) {
         BoxedList* lines = new BoxedList();
         for (BoxedTraceback* wtb = tb; wtb && wtb != None; wtb = static_cast<BoxedTraceback*>(wtb->tb_next)) {
-            lines->ensure(wtb->lines.size());
-            for (auto& line : wtb->lines) {
+            if (wtb->has_line) {
+                auto& line = wtb->line;
                 auto l = BoxedTuple::create({ boxString(line.file), boxString(line.func), boxInt(line.line) });
                 listAppendInternal(lines, l);
             }
@@ -119,9 +114,8 @@ Box* BoxedTraceback::getLines(Box* b) {
     return tb->py_lines;
 }
 
-void BoxedTraceback::Here(LineInfo lineInfo, BoxedTraceback** tb) {
-    *tb = new BoxedTraceback(*tb);
-    (*tb)->addLine(lineInfo);
+void BoxedTraceback::here(LineInfo lineInfo, Box** tb) {
+    *tb = new BoxedTraceback(lineInfo, *tb);
 }
 
 void setupTraceback() {

src/runtime/traceback.h

@@ -27,25 +27,22 @@ class GCVisitor;
 extern "C" BoxedClass* traceback_cls;
 class BoxedTraceback : public Box {
 public:
-    typedef llvm::SmallVector<LineInfo, 1> LinesVector;
     Box* tb_next;
-    LinesVector lines;
+    bool has_line;
+    LineInfo line;
     Box* py_lines;
 
-    BoxedTraceback(LinesVector&& lines) : tb_next(None), lines(std::move(lines)), py_lines(NULL) {}
-    BoxedTraceback(BoxedTraceback* tb_next) : tb_next(tb_next), py_lines(NULL) {}
-    BoxedTraceback() : tb_next(None), py_lines(NULL) {}
+    BoxedTraceback(LineInfo line, Box* tb_next) : tb_next(tb_next), has_line(true), line(line), py_lines(NULL) {}
+    BoxedTraceback() : tb_next(None), has_line(false), line(-1, -1, "", ""), py_lines(NULL) {}
 
     DEFAULT_CLASS(traceback_cls);
 
-    void addLine(const LineInfo line);
-
     static Box* getLines(Box* b);
 
     static void gcHandler(gc::GCVisitor* v, Box* b);
 
     // somewhat equivalent to PyTraceBack_Here
-    static void Here(LineInfo lineInfo, BoxedTraceback** tb);
+    static void here(LineInfo lineInfo, Box** tb);
 };
 
 void printTraceback(Box* b);