[Vulkan] Vulkan backend supports Call::reinterpret and vectorized comparison.

[ajtulloch]

See unit test. This allows us to generate vectorized code for common pointwise operations, which is helpful on some platforms. For e.g. Metal, this lowers to select(true, false, cond), glsl to the vectorized versions, etc. This fixes a bug where we'd unconditionally set the result type of comparison operations to a scalar boolean, which leads to failures downstream.

From the SPIR-V specification, vectorized selections (and comparisons) are explicitly supported.

OpSelect

Select between two objects.

Result Type must be a scalar or vector.

The type of Object 1 must be the same as Result Type. Object 1 is selected as the result if Condition is true.

The type of Object 2 must be the same as Result Type. Object 2 is selected as the result if Condition is false.

Condition must be a scalar or vector of Boolean type. 

It must have the same number of components as Result Type.

Results are computed per component.

 
and

OpUGreaterThan

Unsigned-integer comparison if Operand 1 is greater than Operand 2.

Result Type must be a scalar or vector of Boolean type. 

The type of Operand 1 and Operand 2 must be a scalar or vector of integer type. 

They must have the same component width, and they must have the same number of components as Result Type. 

Results are computed per component.

 

[ajtulloch]

cc @jwfromm, @tqchen

[jwfromm]

LGTM, I'm glad you're taking a look at improving Vulkan efficiency. I think it's one of the most important targets we need to support.

[ajtulloch]

@jwfromm I've rebased and applied clang-format on the other macro decls for consistency.

[ajtulloch]

@tqchen this should be good to go?

[tqchen]

Merged! Thanks @ajtulloch @jwfromm