var result array - bad codegen (null pointer dereference)

[mratsim]

The following test case generates a null pointer dereference in the C code which results in SIGSEGV:

It should probably be catched by #124 or #7373, but I'm not sure how to slice part of
an array with compile-time known boundaries in a way compatible with JS and compile-time function evaluation.

type
  Foo[N: static[int]] = object
    data: array[N, int]

proc lo[N: static[int]](x: Foo[N]): Foo[N div 2] =
  for i in 0 ..< N div 2:
    result.data[i] = x.data[i]

proc lo[N: static[int]](x: var Foo[N]): var Foo[N div 2] =
  for i in 0 ..< N div 2:
    result.data[i] = x.data[i]

proc `lo=`[N: static[int]](x: var Foo[N], y: Foo[N div 2]) =
  for i in 0 ..< N div 2:
    x.data[i] = y.data[i]

let a = Foo[4](data: [1, 2, 3, 4])

echo a
echo a.lo    # OK

var b: Foo[4]

echo b.lo    # crash
b.lo = a.lo  # crash

N_LIB_PRIVATE N_NIMCALL(tyObject_Foo_9ctxI3pPBaeTK4lcwG7MCPQ, lo_axkQ9bkuqVKw9aIqFQKaK0zw)(tyObject_Foo_fudkhWAqx7S1trfINt0x9ag* x) {
	tyObject_Foo_9ctxI3pPBaeTK4lcwG7MCPQ result;
	memset((void*)(&result), 0, sizeof(tyObject_Foo_9ctxI3pPBaeTK4lcwG7MCPQ));
	{
		NI i;
		NI i_2;
		i = (NI)0;
		i_2 = ((NI) 0);
		{
			while (1) {
				if (!(i_2 < ((NI) 2))) goto LA3;
				i = i_2;
				result.data[(i)- 0] = (*x).data[(i)- 0];
				i_2 += ((NI) 1);
			} LA3: ;
		}
	}
	return result;
}

N_LIB_PRIVATE N_NIMCALL(tyObject_Foo_9ctxI3pPBaeTK4lcwG7MCPQ*, lo_JQlhvEq9aj9b5ARpjNX2rtlw)(tyObject_Foo_fudkhWAqx7S1trfINt0x9ag* x) {
	tyObject_Foo_9ctxI3pPBaeTK4lcwG7MCPQ* result;
	result = (tyObject_Foo_9ctxI3pPBaeTK4lcwG7MCPQ*)0;  // <------------ null pointer
	{
		NI i;
		NI i_2;
		i = (NI)0;
		i_2 = ((NI) 0);
		{
			while (1) {
				if (!(i_2 < ((NI) 2))) goto LA3;
				i = i_2;
				(*result).data[(i)- 0] = (*x).data[(i)- 0]; // <------------ dereference
				i_2 += ((NI) 1);
			} LA3: ;
		}
	}
	return result;
}

N_LIB_PRIVATE N_NIMCALL(void, loeq__2v3e0euqbo9bm3oN3Lkc73w)(tyObject_Foo_fudkhWAqx7S1trfINt0x9ag* x, tyObject_Foo_9ctxI3pPBaeTK4lcwG7MCPQ y) {
	{
		NI i;
		NI i_2;
		i = (NI)0;
		i_2 = ((NI) 0);
		{
			while (1) {
				if (!(i_2 < ((NI) 2))) goto LA3;
				i = i_2;
				(*x).data[(i)- 0] = y.data[(i)- 0];
				i_2 += ((NI) 1);
			} LA3: ;
		}
	}
}

[LemonBoy]

Minimal test case:

proc foo(): var array[1,int] = discard
echo foo()