Nested union bug

[Marcus Stojcevich]

Hi,

I noticed a bug with GDC that I cannot reproduce with other 
compilers. I can't seem to create an account on the Bugzilla, so 
I'm reporting it here.

It appears that when you have a union nested within a struct 
which itself is within a union, the union members get placed at 
position 0 of the struct, which is the same position as the first 
struct member. This obviously causes issues.

I can reproduce it with union > struct > union, but not struct > 
union or union > struct.

I created a minimal example that demonstrates the issue. The 
align(1) isn't required for the example to work, but I put it 
there to make sure output is consistent.

===============================
import std.stdio;

union foo {
     long ab;
     struct { align(1):
         int a;
         union {
             int b;
         }
     }
}

void main() {
     foo x;
     writefln("Position of a: %d, b: %d", cast(ulong)(&x.a) - 
cast(ulong)(&x), cast(ulong)(&x.b) - cast(ulong)(&x));
}
===============================


LDC, DMD, and GCC (with equivalent C code) all print
Position of a: 0, b: 4

GDC prints
Position of a: 0, b: 0


My GDC version is 8.2.0, and I am testing with optimizations off.


Thanks in advance for looking at this,
Marcus Stojcevich