Testing GDC (GCC 7.1) on Runtime-less ARM Cortex-M

[Iain Buclaw via D.gnu]

On 25 June 2017 at 12:18, Mike via D.gnu <d.gnu at puremagic.com> wrote:
> This is just an experience report for those who might be interested.
>
> Given this pull request (https://github.com/D-Programming-GDC/GDC/pull/456)
> I thought I'd try testing a more recent GDC with my STM32 demo
> (https://github.com/JinShil/stm32f42_discovery_demo) and see what the state
> of things is.  Here are my results.
>
> TypeInfo Stubs
> ===============
> I was able to reduce object.d down to the following:
>
> -- object.d --
> module object;
>
> alias size_t    = typeof(int.sizeof);
> alias ptrdiff_t = typeof(cast(void*)0 - cast(void*)0);
>
> alias string = immutable(char)[];
>
> class Object
> { }
>
> class TypeInfo
> { }
>
> class TypeInfo_Const : TypeInfo
> {
>     size_t getHash(in void *p) const nothrow { return 0; }
> }
> ----------------------
>
> I wasn't able to completely omit TypeInfo because for some reason the
> compiler is still looking for `getHash` in `TypeInfo_Const`.
>
> -- output from gdc --
> object.d:1:1: error: class object.TypeInfo_Const is forward referenced when
> looking for 'getHash'
>  module object;
>  ^
> cc1d: error: no property 'getHash' for type 'object.TypeInfo_Const'

This would be coming from the front-end. The only functions that gdc
itself generates are for ModuleInfo, all other artificial data and
routines are emitted because the compiler was told to.


> -----------------------
>
> But, most of the `TypeInfo` stubs are no longer required.
>
> TypeInfo Bloat
> ===============
> Unfortunately the TypeInfo bloat documented here
> (https://issues.dlang.org/show_bug.cgi?id=14758) is still there.  I suppose
> that's to be expected as it appears the aforementioned pull request only
> removed the need to write `TypeInfo` stubs.
>
> Binary size for the STM32 demo is about 600kB when it should be more like
> 6kB.
>

Out of curiosity, is that the original built binary, or post trimming
(strip / --gc-sections)?

There might be a size optimization possibility putting the TypeInfo in
comdat, perhaps we could give that a go.

There's also https://github.com/D-Programming-GDC/GDC/pull/100 -
perhaps there should be a revival of that.

> Compile Speed
> =============
> It takes about 1 minute 30 seconds to build and link the STM32 demo
> resulting in a 6kB binary.  That's pretty bad, but I suspect that's a DMD
> CTFE problem.
>

Thanks for the update.

Iain.