[Issue 3521] Optimized code access popped register

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=3521



--- Comment #2 from Don <clugdbug at yahoo.com.au> 2009-11-27 00:15:10 PST ---
I investigated this a bit, so far without success. I'm writing notes here for
when I come back to it.
It's something to do with the register allocation. The compiler is somehow
forgetting that it already assigned a register for c when doing the assignment.
I removed the assert to make disassembly even easier: this hits a breakpoint
only when compiled with -O. It only happens if c is zero. You can change the !=
into any kind of comparison, and the c=200 into c+=200, without affecting the
bug. However, changing it into ((c = 200)!=*a) avoids the bug.

void crash(int x)
{
  if (x==200) return;
   asm { int 3; }
}

void bug3521(int *a){
    int c = 0;
    *a = 0;
    if ( *a || (*a != (c = 200)) ) 
       crash(c);
}

void main (){
   int x;
   bug3521(&x);
}

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