Closes the gap left by 7a08197, which refused sequence mode under OpenCL. That
was defensible for a private build and not for a shipped one: the release path
includes an OpenCL laptop, and a customer with a GPU would have found LSTM and
HYBRID simply unavailable.
One launch PER TIMESTEP rather than a single kernel looping with barrier().
Every hidden unit's gates read all of h_{t-1}, OpenCL barriers only span a
work-group, and nothing here constrains how the runtime partitions the global
size - so an in-kernel loop would be correct only by luck of the partitioning.
Host-driven launches make each step an implicit global barrier: more enqueues,
correct on every device.
Backward reuses the buffers the single-timestep path leaves idle in sequence
mode - ConcatenatedGradient (4H) for gate gradients, HiddenCache (H) for dh,
Memory (2H) for dc - so BPTT costs no extra allocations. dW is zeroed once and
accumulated across steps, matching the fused DLL kernel.
Verification available on this machine has limits worth recording. The math is
the same as CPU_LSTMSeqForward/Backward, which is gradient-checked to 2.3e-10;
the kernels are syntax/type-checked offline (DirectML\opencl_seq_syntax_check.cpp,
compiled as C++ with OpenCL shims) because there is no OpenCL device or ICD
here. That check exists because a typo in Network.cl fails the WHOLE program
build, which would take the dense and conv kernels down with it - not just the
new ones. KernelCreate results are now checked and reported for these four for
the same reason; a build failure degrades to "LSTM/HYBRID unavailable on this
device" instead of an Execute error mid-training.
STILL NEEDS A RUN ON REAL OPENCL HARDWARE before release.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
