For a while now GDC and LDC have supported a variety of their backend's attributes, like inlining or compiling a specific function with SSE4 in an otherwise generic x64 build.

I think we should unify those into a common core.attribute, either aliasing or replacing the vendor specific symbols. They don't need to be functional immediately. There are two things that I see need to be discussed.

1. Syntax

  All attributes are currently set via @attribute(…). I wonder
  if this is just easier to recognize for the compiler than
  multiple attribute names or if there are other benefits.
  Personally for the most part I'd prefer shorter versions,
  e.g. @forceinline instead of @attribute("forceinline").
  We can also achieve this by keeping the vendor specific
  modules/symbols and creating aliases, so it is mostly about
  what we prefer.

2. Semantics

  Unfortunately the compiler internals are all quite
  different. When it comes to always inlining a function for
  example, DMD won't even try unless "-inline" is given on the
  command-line. GCC will fail compilation if it cannot inline
  and I think LLVM only warns you in such cases.
  My somewhat painful idea is to split these attributes up
  into something like @forceinline (produces warning or error)
  and @inline (silent or warning at most) and map them to the
  closest the respective compilers can offer - or else make
  them a noop.


https://github.com/mleise/fast/blob/master/source/fast/helpers.d#L99 shows how we alias existing attributes or make them noops:

  version (DigitalMars)
  {
  	enum noinline;
  	enum forceinline;
  	enum sse4;
  }
  else version (GNU)
  {
  	import gcc.attribute;
  	enum noinline    = gcc.attribute.attribute("noinline");
  	enum forceinline = gcc.attribute.attribute("forceinline");
  	enum sse4        = gcc.attribute.attribute("target", "sse4");
  }
  else version (LDC)
  {
  	import ldc.attribute;
  	enum noinline    = ldc.attribute.attribute("noinline");
  	enum forceinline = ldc.attribute.attribute("alwaysinline");
  	enum sse4;
  }

(Note that GCC's target attribute can actually takes a list of features.) If you target i586 and started using SSE, the compiler would tell you that these instructions do not exist on that architecture. So you write a generic function and an additional SSE function with @attribute("target", "sse") and wont run into "illegal instruction" errors at runtime on older CPUs.

-- 
Marco

On Tuesday, 20 October 2015 at 07:57:29 UTC, Marco Leise wrote:
> For a while now GDC and LDC have supported a variety of their backend's attributes, like inlining or compiling a specific function with SSE4 in an otherwise generic x64 build.
>
> I think we should unify those into a common core.attribute, either aliasing or replacing the vendor specific symbols. They don't need to be functional immediately. There are two things that I see need to be discussed.

I couldn't agree more.
It's awkward having to write such boilerplate code just to get something as common as @inline to compile across compilers.
Another example: https://github.com/JinShil/stm32f42_discovery_demo/blob/d61819015/source/runtime/object.d#L16

And for embedded applications @used, @section(".xy") and @weak would also be useful.