CALLER_SAVE/RESTORE in CCalls

[Simon Marlow]

Hi Sven, welcome back :)

>         ...
> 	CALLER_SAVE_SYSTEM
> 	{
> 	StgFloat _ccall_arg1=3D(StgFloat)0.75;
> 	StgFloat _ccall_arg2=3D(StgFloat)0.25;
> 	StgFloat _ccall_arg3=3D(StgFloat)0.0;
> 	(glVertex3f((_ccall_arg1),(_ccall_arg2),(_ccall_arg3)));
> 	}
> 	CALLER_RESTORE_SYSTEM   // !!!
> 	CALLER_SAVE_SYSTEM      // !!!
> 	{
> 	StgFloat _ccall_arg1=3D(StgFloat)0.75;
> 	StgFloat _ccall_arg2=3D(StgFloat)0.75;
> 	StgFloat _ccall_arg3=3D(StgFloat)0.0;
> 	(glVertex3f((_ccall_arg1),(_ccall_arg2),(_ccall_arg3)));
> 	}
> 	CALLER_RESTORE_SYSTEM
>         ...
>=20
> gcc is/was clever enough to omit the code for the marked=20
> lines. Changing
> this in PprAbsC looks easy, or do I miss something here?

Well, arguably the current version is more correct, since the ccall
arguments might refer to certain STG registers.  However, it shouldn't
do any harm to re-order things as you suggest.

> And a related question: What's the reason for the local vars=20
> in the above
> calls? The following looks a bit simpler:
>         ...
> 	CALLER_SAVE_SYSTEM
> 	glVertex3f(((StgFloat)0.75, (StgFloat)0.25, (StgFloat)0.0);
> 	CALLER_RESTORE_SYSTEM   // !!!
> 	CALLER_SAVE_SYSTEM      // !!!
> 	glVertex3f(((StgFloat)0.75, (StgFloat)0.75, (StgFloat)0.0);
> 	CALLER_RESTORE_SYSTEM
>         ...
>=20
> Apart from that, the generated code looks quite cool.

I think the reason for putting the arguments into local vars is for
casms: if a casm refers to a particular arg twice, for example, it won't
duplicate the expression.

Cheers,
	Simon