The prototype implementation of the above specification is vailable as the
simd branch of GHC.
Vectors of the following types are implemented:
Fixed and variable sized vectors
For each type, currently only one vector width is implemented, namely the width that is appropriate for SSE2. This means that vectors are currently all 16 bytes in size.
Only the LLVM code generator is supported.
The implementation differs from the proposal in its naming scheme. We wanted to avoid overloading the term "vector," so, e.g., a 4-wide SIMD vector of
Float#s is a
Native vector sizes
This is unimplemented. Instead we define a higher-level
Multi data family whose instance is platform-dependent. For example, a
Multi Int is represented using an
Int32X4# on a 32-bit platform, and by a
Int64X2# on a 64-bit platform.
ABIs and calling conventions
Integrating variable-sized vectors with GHC's calling convention is a challenge. How many new registers do we add? Do we add registers for each vector type? The correct approach is unclear, so the current implementation passes all SIMD vectors on the stack.
Memory alignment for vectors
The implementation does not attempt to align memory containing SIMD vectors. SIMD vector loads and stores do not assume alignment.