bad.diff

  (func $ThreadMain\28void*\29 (param $0 i32) (result i32)
   (local $1 i32)
   (local $2 i32)
   (loop $label$1
    (local.set $0
     (call $__cxa_allocate_exception
      (i32.const 4)
     )
    )
    (block $label$2
     (block $label$3
      (block $label$4
       (if
        (i32.and
         (local.get $1)
         (i32.const 3)
        )
        (block
         (i32.store
          (local.get $0)
          (i32.const 1078530000)
         )
         (i32.store
-         (i32.const 2948)
+         (i32.const 0)
          (i32.const 0)
         )
         (call $invoke_viii
          (i32.const 1)
          (local.get $0)
          (i32.const 1452)
          (i32.const 0)
         )
         (local.set $0
          (i32.load
-          (i32.const 2948)
+          (i32.const 0)
          )
         )
         (i32.store
-         (i32.const 2948)
+         (i32.const 0)
          (i32.const 0)
         )
         (br_if $label$3
          (i32.ne
           (local.get $0)
           (i32.const 1)
          )
         )
         (br $label$4)
        )
       )
       (i32.store
        (local.get $0)
        (local.get $1)
       )
       (i32.store
-       (i32.const 2948)
+       (i32.const 0)
        (i32.const 0)
       )
       (call $invoke_viii
        (i32.const 1)
        (local.get $0)
        (i32.const 1440)
        (i32.const 0)
       )
       (local.set $0
        (i32.load
-        (i32.const 2948)
+        (i32.const 0)
        )
       )
       (i32.store
-       (i32.const 2948)
+       (i32.const 0)
        (i32.const 0)
       )
       (br_if $label$3
        (i32.ne
         (local.get $0)
         (i32.const 1)
        )
       )
      )
      (local.set $0
       (call $__cxa_find_matching_catch_4
        (i32.const 1440)
        (i32.const 1452)
       )
      )
      (if
       (i32.eq
        (local.tee $2
         (call $getTempRet0)
        )

exceptions.cpp

// Copyright 2019 The Emscripten Authors.  All rights reserved.
// Emscripten is available under two separate licenses, the MIT license and the
// University of Illinois/NCSA Open Source License.  Both these licenses can be
// found in the LICENSE file.

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <assert.h>
#include <emscripten.h>

#include <atomic>

#define NUM_THREADS 2
#define TOTAL 1000
#define THREAD_ADDS 750
#define MAIN_ADDS 5

static std::atomic<int> sum;
static std::atomic<int> total;

void *ThreadMain(void *arg) {
  for (int i = 0; i < TOTAL; i++) {
    try {
      // Throw two different types, to make sure we check throwing and landing
      // pad behavior.
      if (i & 3) {
        throw 3.14159f;
      }
      throw i;
    } catch (int x) {
      total += x;
    } catch (float f) {
      sum++;
      // wait for a change, so we see interleaved processing.
      int last = sum.load();
      while (sum.load() == last) {}
    }
  }
  pthread_exit((void*)TOTAL);
}

pthread_t thread[NUM_THREADS];

void CreateThread(int i)
{
  pthread_attr_t attr;
  pthread_attr_init(&attr);
  pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
  static int counter = 1;
  int rc = pthread_create(&thread[i], &attr, ThreadMain, (void*)i);
  assert(rc == 0);
  pthread_attr_destroy(&attr);
}

void loop() {
  static int main_adds = 0;
  int worker_adds = sum.load() - main_adds;
  sum++;
  main_adds++;
  printf("main iter %d : %d\n", main_adds, worker_adds);
  if (worker_adds == NUM_THREADS * THREAD_ADDS &&
      main_adds >= MAIN_ADDS) {
    printf("done: %d.\n", total.load());
    emscripten_cancel_main_loop();
    exit(0);
  }
}

int main() {
  // Create initial threads.
  for(int i = 0; i < NUM_THREADS; ++i) {
    printf("maek\n");
    CreateThread(i);
  }

  emscripten_set_main_loop(loop, 0, 0);
}