Big problem with Small programs

[kris]

Walter Bright wrote:
> kris wrote:
> 
>> I have a helloworld.d program. I compile it on both Win32 and on 
>> linux. On linux, the executable is 72KB whereas on Win32 it is 141KB. 
>> Why is this?
>>
>> Turns out that D programs importing comprehensive Win32 D headers will 
>> wind up with executable space occupied for *all* constants and *all* 
>> struct initializers for the darned Win32 decls; where none of them are 
>> actually used.
>>
>> That amounts to ~70KB of junk in the executable -- almost a full 100% 
>> increase in size beyond what it should be.
>>
>> Does OptLink remove this? I've had no success with it. Walter? Can you 
>> help with this?
>>
>> - Kris
> 
> 
> Try using enums instead of const variables, they don't take up any space 
> in the object file.

Thanks, but that makes only a dent in the overhead.

One might assume that dmd and optlink have no facilities to remove 
unreferenced entities such as these? If so, doesn't this seem to be a 
notable weak point in the toolchain?

Why is this not an issue with C/C++ ?

1) C used true compile-time constants via #define. From your comment 
above, it would appear enum is the equivalent in D, rather than const 
int. Probably worth a note in the doc about that?

2) C does not have struct inititalizers.

Why has this not come to light before? Well, the Phobos Win32 headers 
are pretty darned slim compared with the real mcCoy. There's been a lot 
of clamour for 'real' win32 headers for years. Now that we have them, 
we're penalized for using 'em :p

Surely there must be some way for the linker to identify and discard 
unused entities?

Another approach would be to make the win32 headers be .di files, such 
that no obj files are generated. However, this breaks quickly whenever 
one uses a struct requiring an initializer (link errors).

Enum is only a small partial resolution here, and we need to complete 
the picture somehow. Any other suggestions, Walter? Can you tag the 
structs internally somehow to make the linker discard the unused ones? 
Can you explain exactly what's going on, such that others might be able 
to suggest something?

- Kris