RE: _Cilk_spawn and _Cilk_sync for C++

[Iyer, Balaji V]

> -----Original Message-----
> From: Jason Merrill [mailto:ja...@redhat.com]
> Sent: Thursday, November 28, 2013 9:11 AM
> To: Iyer, Balaji V; gcc-patches@gcc.gnu.org
> Cc: Jeff Law
> Subject: Re: _Cilk_spawn and _Cilk_sync for C++
> 
> On 11/27/2013 11:05 PM, Iyer, Balaji V wrote:
> > Found the bug. I was not utilizing the stabilize_expr's output correctly.
> 
> Unfortunately, I think I was misleading you with talk of stabilize; like you 
> said,
> you want to evaluate the whole expression in the spawned function rather
> than in the caller, so that any temporaries (including the lambda closure) 
> live
> until the _Cilk_sync.  Using stabilize_expr this way (the way I was 
> suggesting)
> forces the lambda closure to be evaluated in the caller, and then destroyed
> at the end of the enclosing statement, which is likely to erase any data that
> the spawned function needs to do its work, if anything captured by copy has
> a destructor.
> 
> As I said in my last mail, I think the right fix is to make sure that A gets
> remapped properly during copy_body so that its use in the initializer for the
> closure doesn't confuse later passes.

Ok. I think I cut and pasted the wrong part. I am very sorry about it.

Here is the original code:

  global_var = 0;
  _Cilk_spawn [=](int *Aa, int size){ foo1_c(A, size); }(B, 2);
  foo1 (A, 2);
  _Cilk_sync;
  if (global_var != 2)
    return (++q);

Here is the gimple output with _Cilk_spawn and _Cilk_sync *DISABLED*

try
    {
      A[0] = 5;
      A[1] = 3;
      B[0] = 5;
      B[1] = 3;
      main_size = argc + 1;
      q = 0;
      global_var = 0;
      D.2219.__A = A;
      try
        {
          main2(int)::<lambda(int*, int)>::operator() (&D.2219, &B, 2);
        }
      finally
        {
          D.2219 = {CLOBBER};
        }
      foo1 (&A, 2);
      global_var.4 = global_var;
      if (global_var.4 != 2) goto <D.2255>; else goto <D.2256>;
      <D.2255>:
      q = q + 1;
      D.2257 = q;
      return D.2257;
      <D.2256>:
      D.2257 = q;
      return D.2257;
    }
  finally
    {
      A = {CLOBBER};
      B = {CLOBBER};
    }

Here is the gimple output with _Cilk_spawn and _Cilk_synd enabled
try
    {
      try
        {
          __cilkrts_enter_frame_fast_1 (&D.2258);
          D.2351 = D.2258.worker;
          D.2352 = D.2351->pedigree.rank;
          D.2258.pedigree.rank = D.2352;
          D.2353 = D.2258.worker;
          D.2354 = D.2353->pedigree.parent;
          D.2258.pedigree.parent = D.2354;
          D.2355 = D.2258.call_parent;
          D.2356 = D.2258.worker;
          D.2357 = D.2356->pedigree.rank;
          D.2355->pedigree.rank = D.2357;
          D.2358 = D.2258.call_parent;
          D.2359 = D.2258.worker;
          D.2360 = D.2359->pedigree.parent;
          D.2358->pedigree.parent = D.2360;
          D.2361 = D.2258.worker;
          D.2361->pedigree.rank = 0;
          D.2362 = D.2258.worker;
          D.2362->pedigree.parent = &D.2258.pedigree;
          __cilkrts_detach (&D.2258);
          B.5 = &CHAIN.7->B;
          D.2219.__A = CHAIN.7->A;
          try
            {
              main2(int)::<lambda(int*, int)>::operator() (&D.2219, B.5, 2);
            }
          finally
            {
              D.2219 = {CLOBBER};                                     
<================ CLOBBERING LINE
            }
        }
      catch
        {
          catch (NULL)
            {
              try
                {
                  D.2364 = D.2258.flags;
                  D.2365 = D.2364 | 16;
                  D.2258.flags = D.2365;
                  D.2366 = __builtin_eh_pointer (0);
                  D.2258.except_data = D.2366;
                  D.2367 = __builtin_eh_pointer (0);
                  __cxa_begin_catch (D.2367);
                  __cxa_rethrow ();
                }
              finally
                {
                  __cxa_end_catch ();
                }
            }
        }
    }
  finally
    {
      D.2368 = D.2258.worker;
      D.2369 = D.2258.call_parent;
      D.2368->current_stack_frame = D.2369;
      __cilkrts_pop_frame (&D.2258);
      D.2370 = D.2258.flags;
      if (D.2370 != 16777216) goto <D.2371>; else goto <D.2372>;
      <D.2371>:
      __cilkrts_leave_frame (&D.2258);
      goto <D.2373>;
      <D.2372>:
      <D.2373>:
    }
}

In this line (<=====) it is clobbering the lambda closure. 

Sorry again about the mistake.

By the way, I have only cut and pasted the part from the top-level try 
expression to just show the relevant part. If you want, I can show you the rest.

> 
> Jason