[LLVMdev] Instruction pattern type inference problem

[Morten Ofstad]

Christopher Lamb wrote:
> A strategy that we have had luck with in the past is the concept of a 
> "vector boolean" type, which is the result of a comparison between two 
> vectors. It's then necessary to perform a reduction (and, or) on the 
> elements in order to produce a scalar boolean value that's suitable for 
> a branch. This also allows stuff like letting 'select' accept a vector 
> boolean predicate and vector values to perform a vector select.

this is the semantics that GLSL uses for vector compares, for example the signature of one of the overloads for the 
built-in function 'lessThan' is:

bvec4 lessThan(vec4 x, vec4 y)

what I wanted to mention are the built-in functions 'any' and 'all' which have signatures (for 4-vectors)

bool any(bvec4 x)
bool all(bvec4 x)

and the obvious semantics any(x)= x.x || x.y || x.z || x.w and all(x)= x.x && x.y && x.z && x.w -- I think if vector 
comparisions and vector boolean types are added to LLVM, it would also be very nice to have the 'any' and 'all' added as 
intrinsics...

m.