[LLVMdev] correctness in localized global variable between setjmp and longjmp

[Balaram Makam]

I noticed that c code below failed with -O3 : 

 

#include <setjmp.h>

#include <stdio.h>

 

static int cnt;

 

int main(){

  int var;

  jmp_buf buffer;

  cnt = 0;

 

  if ((var = setjmp(buffer)) == 0) {

    printf(" if true, var: %d, .count:%d , increase count !\n",var, cnt);

    cnt++;

    longjmp(buffer, 2);

  } else {

    if (cnt == 1)

      printf(" Pass      var: %d, .count:%d \n",var, cnt);

    else

      printf(" Fail !!!  var: %d, .count:%d \n",var, cnt);

  }

  return 0;

}

 

The documentation of setjmp/longjmp says that the values of objects of
automatic storage duration which are local to the function containing the
invocation of the corresponding setjmp() which do not have
volatile-qualified type and which are changed between the setjmp()
invocation and longjmp() call are indeterminate.

 

Even though "cnt" is a global variable, above c code failed because the
globalopt pass localizes the global value (cnt) in main(), causing that the
value of the global variable becomes indeterminate between setjmp() and
longjmp. I believe the globalopt pass need to check this case before
localizing global variables. Is there any better solution about it?

 

Thanks,

Balaram

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