[PATCH] Allow casts of mixed-size same-arity vectors

[Hal Finkel]

----- Original Message -----
> 
> On Sep 12, 2013, at 2:08 PM, Hal Finkel <hfinkel at anl.gov> wrote:
> 
> > ----- Original Message -----
> >> 
> >> On Wed, Sep 11, 2013 at 3:34 PM, Hal Finkel < hfinkel at anl.gov >
> >> wrote:
> >> 
> >> ----- Original Message -----
> >>> On Sep 11, 2013, at 3:29 PM, Hal Finkel < hfinkel at anl.gov >
> >>> wrote:
> >>> 
> >>> 
> >>> 
> >>> 
> >>> 
> >>> ----- Original Message -----
> >>> 
> >>> 
> >>> ----- Original Message -----
> >>> 
> >>> 
> >>> Hal —
> >>> 
> >>> Am I understanding this correctly:
> >>> 
> >>> vector4float x;
> >>> vector4int16 y = (vector4int16)x; // this is a conversion
> >>> vector4int32 z = (vector4int32)x; // this is a bitcast
> >>> 
> >>> This seems confusing in the extreme.
> >>> 
> >>> On the other hand, I don't really like the implied int-to-float
> >>> bitcast semantics. Maybe it would be better to just add a warning
> >>> for this case. What do you think?
> >>> 
> >>> bitcast semantics for vector casts are an essential tool for SIMD
> >>> programming. Essentially all warnings generated would be false
> >>> positives.
> >> 
> >> Do you specifically mean in OpenCL, or generally? (I've worked on
> >> SIMD special function implementations, so I understand the
> >> utility).
> >> 
> >> OpenCL doesn't allow writing casts like this at all, if that's
> >> what
> >> you're asking; OpenCL requires using intrinsics.
> > 
> > So is there already an intrinsic that does what I want here?
> 
> In OpenCL there are ~5000 of them (IIRC), yes.

OIC, all of the convert_* functions.

I've been thinking about constructing a patch to implement __builtin_vectorconvert(type, value), do you think that is a reasonable approach?

Thanks again,
Hal

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory