Invalid semicolons get inserted when using certain define macros.

For example, the well known do { stuff; } while (0) macro wrapper trick expands incorrectly.'

Example:

#define foo(x) do { return (x); } while (0)

int f(int num)
{
  if (num > 0)
    foo(num);
  else
    return num * num;
}

Expands into

int f(int num)
{
  if(num > 0) do {
    return (num);
  } while(0);
  
  ;
  else return num * num; 
}

Which has incorrectly inserted an additional semicolon between the if/else blocks (or automatically inserted one after while(0), causing the original semicolon to be pushed between blocks)