store and restore is_reraise flag

I did not trigger this bug (also could not come up with a test) but just by inspecting the code I thought it's very suspicious.

But I did remove the assert(!exc_state.is_reraise) assert because it got hit in a legitimate case,
(c++ exception got rethrowen in the llvm tier, cought in our c++ code and rethrowen because of api mismatch. With no python code in between.)

src/codegen/unwinding.cpp

@@ -545,14 +545,17 @@ public:
         stat.log();
     }
 
-    std::tuple<FrameInfo*, ExcInfo, PythonStackExtractor> pause() {
+    std::tuple<FrameInfo*, ExcInfo, PythonStackExtractor, bool> pause() {
         static StatCounter stat("us_unwind_session");
         stat.log(t.end());
-        return std::make_tuple(std::move(prev_frame_info), std::move(exc_info), std::move(pystack_extractor));
+        bool is_reraise = getIsReraiseFlag();
+        getIsReraiseFlag() = false;
+        return std::make_tuple(std::move(prev_frame_info), std::move(exc_info), std::move(pystack_extractor),
+                               is_reraise);
     }
 
-    void resume(std::tuple<FrameInfo*, ExcInfo, PythonStackExtractor>&& state) {
-        std::tie(prev_frame_info, exc_info, pystack_extractor) = state;
+    void resume(std::tuple<FrameInfo*, ExcInfo, PythonStackExtractor, bool>&& state) {
+        std::tie(prev_frame_info, exc_info, pystack_extractor, getIsReraiseFlag()) = state;
         t.restart();
     }
 
@@ -620,11 +623,12 @@ public:
             // make sure that our libunwind based python frame handling and the manual one are the same.
             assert(prev_frame_info == getTopFrameInfo());
 
-            if (exceptionAtLineCheck()) {
+            if (!getIsReraiseFlag()) {
                 // TODO: shouldn't fetch this multiple times?
                 frame_iter.getCurrentStatement()->cxx_exception_count++;
                 exceptionAtLine(&exc_info.traceback);
-            }
+            } else
+                getIsReraiseFlag() = false;
         }
     }
 };

src/codegen/unwinding.h

@@ -59,8 +59,10 @@ void unwindingThroughFrame(PythonUnwindSession* unwind_session, unw_cursor_t* cu
 
 // TODO move these to exceptions.h
 void logException(ExcInfo* exc_info);
-void startReraise();
-bool exceptionAtLineCheck();
+bool& getIsReraiseFlag();
+inline void startReraise() {
+    getIsReraiseFlag() = true;
+}
 void exceptionAtLine(Box** traceback);
 void caughtCxxException(ExcInfo* exc_info);
 extern "C" void caughtCapiException();

src/runtime/exceptions.cpp

@@ -299,30 +299,20 @@ void caughtCxxException(ExcInfo* exc_info) {
     exceptionAtLine(&exc_info->traceback);
 }
 
-
-
 struct ExcState {
     bool is_reraise;
     constexpr ExcState() : is_reraise(false) {}
 } static __thread exc_state;
 
-bool exceptionAtLineCheck() {
-    if (exc_state.is_reraise) {
-        exc_state.is_reraise = false;
-        return false;
-    }
-    return true;
+bool& getIsReraiseFlag() {
+    return exc_state.is_reraise;
 }
 
 void exceptionAtLine(Box** traceback) {
-    if (exceptionAtLineCheck()) {
+    if (!getIsReraiseFlag())
         PyTraceBack_Here_Tb((struct _frame*)getFrame((FrameInfo*)cur_thread_state.frame_info),
                             (PyTracebackObject**)traceback);
-    }
-}
-
-void startReraise() {
-    assert(!exc_state.is_reraise);
-    exc_state.is_reraise = true;
+    else
+        getIsReraiseFlag() = false;
 }
 }