[cfe-dev] [LLVMdev] [PATCH] OpenCL half support

[Anton Lokhmotov]

Hi Chris,

> Does the spec force evaluation to happen in half mode, or does it
> specify that there is a promotion to float (or some other type), an
> operation, then truncation back to half?

The last paragraph in section 9.6 says: "NOTE: Implementations may perform
floating-point operations on half scalar or vector data types by converting
the half values to single precision floating-point values and performing the
operation in single precision floating-point. In this case, the
implementation will use the half scalar or vector data type as a storage
only format."

That is, an implementation may perform operations on half scalar and vector
values either using half-precision operations (if supported natively) or
using single-precision operations (always supported natively).  In either
case, it's desirable to represent half operations in the IR, and let the
backend make the decision.

Cheers,
Anton.