Fix dim shared byref initializer check

[dkl]

global ref initializers were not checked for being non-constant, but that can actually matter. For example when trying to initialize a ref from another ref, the second ref will try to copy the first ref's value, which is a non-constant initializer that isn't possible without generating a global constructor.

So for now I think the best solution is to disallow the case - at least fbc doesn't crash anymore.

[jayrm]

Looks good to deal with the const initializer checks.

My only recommendation is, that after this PR is merged, is to close 814, 822, 842, and start a new ticket for the following:

bug ticket 822 has this example:

Type UDT1
    Dim As Integer I1
End Type

Type UDT2
    Dim As Integer I2
    Static Byref As UDT1 ru1
End Type

Dim Byref As UDT1 UDT2.ru1 = *Cast(UDT1 Ptr, 0)

So we can still arrive at a failed assertion assert( expr <> NULL ) hFlushExprStatic(), but I think this is a separate issue from the initial 822 bug report, and it would be easier to track as separate issue.

[dkl]

Ok, that one is also interesting. Turns out the CONST code path (as opposed to the OFFSET code path) in hFlushExprStatic() didn't consider that a ref actually is a pointer and tried to do astNewCONV() from the type-casted null pointer initree (pointer type) to the symbol type (struct). The new commit should fix that.

[jayrm]

You make it look so easy. I struggled with this for days. You are at about the spot I got stuck trying to convert the LHS sym to just a pointer. x86 emitter doesn't know what to do with FB_DATATYPE_STRUCT in EMITVARINII.

[jayrm]

In ten years I have never seen ".invalid" come up in x86 -gen gas. Could use dtype = FB_DATATYPE_STRUCT to mean reference to struct. i.e. only time would ever pass STRUCT is that it is a ref to STRUCT. Maybe.

In emit_x86.bas:EMITVARINII()

	case FB_DATATYPE_STRUCT, FB_DATATYPE_POINTER
		'' reference to struct or pointer
		function = @".long"
	case FB_DATATYPE_STRING
		function = @".INVALID"

Will allow this...

type udt1
	dim as integer i1
end type

type udt2
	dim as integer i2
	static byref as udt1 ru1
end type

dim byref as udt1 udt2.ru1 = *cast(udt1 ptr, 55)

print @udt2.ru1 '' returns 55

to succeed.

[jayrm]

sfulldtype has same value as sdtype throughout.

[dkl]

oops; fixed it.

[jayrm]

if this is removed....

[jayrm]

... then this should be if( edtype <> sfulldtype ) then

[jayrm]

There is a lower level issue going on here in either x86 IR or x86 emitter. -gen gcc seems to handle it this change OK, but -gen gas does not. My previous comment is incorrect about replacing ".invalid" for structures in the x86 emitter.

For example, this succeeds for integer but not for byte

Type UDT
	Dim As Integer I
	Static Byref As byte RI
End Type

Dim Byref As byte UDT.RI = *Cast(byte Ptr, 123456)

print @UDT.RI

but will give other ASM errors when emitted.