Re: opaque vector types?

[Michael Meissner <meissner@linux.vnet.ibm.com>]

On Wed, May 06, 2009 at 02:29:46AM -0400, DJ Delorie wrote:
> 
> Andrew Pinski <pinskia@gmail.com> writes:
> > You could do what the rs6000 back-end does for the altivec builtins
> > and resolve them while the parser is run (the SPU back-end does the
> > same thing too).  Yes there are opaque vector types, you just use
> > build_opaque_vector_type instead of build_vector_type.
> 
> Thanks, I'll look at those.  Any way to prototype such functions in C ?

As Andrew says the rs6000/spu have the notion of overloaded builtins.  I've
been working in this area somewhat for the power7 port, and you might want to
look at my power7-branch.

In rs6000.h it uses REGISTER_TARGET_PRAGMAS to set the
resolve_overloaded_builtin target hook:

/* Target pragma.  */
#define REGISTER_TARGET_PRAGMAS() do {				\
  c_register_pragma (0, "longcall", rs6000_pragma_longcall);	\
  targetm.resolve_overloaded_builtin = altivec_resolve_overloaded_builtin; \
} while (0)

In rs6000-c.c you have the function that tries to resolve the builtin given the
argument types:

tree
altivec_resolve_overloaded_builtin (tree fndecl, void *passed_arglist)
{
	...
}

It returns a tree of the builtin function with the appropriate types.  In the
code, there is a giant table (altivec_overloaded_builtins) that maps the
generic builtin functions to the specific ones based on the argument types.

For example, altivec has a builtin function that does absolute value for any
vector type, and internally it converts this to the appropriate builtin for
each type:

const struct altivec_builtin_types altivec_overloaded_builtins[] = {
  /* Unary AltiVec/VSX builtins.  */
  { ALTIVEC_BUILTIN_VEC_ABS, ALTIVEC_BUILTIN_ABS_V16QI,
    RS6000_BTI_V16QI, RS6000_BTI_V16QI, 0, 0 },
  { ALTIVEC_BUILTIN_VEC_ABS, ALTIVEC_BUILTIN_ABS_V8HI,
    RS6000_BTI_V8HI, RS6000_BTI_V8HI, 0, 0 },
  { ALTIVEC_BUILTIN_VEC_ABS, ALTIVEC_BUILTIN_ABS_V4SI,
    RS6000_BTI_V4SI, RS6000_BTI_V4SI, 0, 0 },
  { ALTIVEC_BUILTIN_VEC_ABS, ALTIVEC_BUILTIN_ABS_V4SF,
    RS6000_BTI_V4SF, RS6000_BTI_V4SF, 0, 0 },
    ...
};

-- 
Michael Meissner, IBM
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