[ExecuTorch][WebGPU] Add optimized gelu op#20843
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🔗 Helpful Links🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/20843
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[ExecuTorch][WebGPU] Add relu op (shared unary handler; sigmoid adopts make_compute_pipeline)
#20863
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This was referenced Jul 10, 2026
This was referenced Jul 16, 2026
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Stack from ghstack (oldest at bottom):
Adds the
geluactivation to the WebGPU backend. GELU is the feed-forward (MLP) activation in the vision and VLM transformer blocks this backend targets — the Florence-2 DaViT encoder, BART, and the Whisper/Voxtral stacks — so it is on the critical path for delegating those models without graph breaks.Problem — The WebGPU backend had no
aten.gelu.defaultkernel, so any model whose FFN uses GELU could not be fully delegated. PyTorch's default is the exact (erf) formulation, and the target encoders use it; the tanh approximation must also be supported.Solution
aten.gelu.defaultwas unsupported — no kernel, forcing a partition break around every GELU.gelu.wgslcomputes GELU on the GPU. The exact (erf) vs tanh choice is resolved by compiling the matching entry point (main_erf/main_tanh) into the pipeline, so each dispatch runs only its own formula — no per-invocationselect()and no double-eval of both branches.Implementation
select()-guarded scalar reads, computes GELU as onevec4<f32>op, and scatters back only the in-bounds lanes — so arbitrary FFN widths that are not a multiple of 4 are handled without a separate remainder pass.0.5*x*(1+tanh(...))form.approximatearg (args[1]: "none" selects erf, anything else selects tanh) picks the entry point at build time through the sharedutils::make_compute_pipeline; workgroup size comes fromutils::clamp_workgroup_size, the dispatch count fromutils::compute_1d_workgroup_count, and the uniform fromutils::make_uniform.backends/vulkan/runtime/graph/ops/impl/UnaryOp.cpp(itsgeluhandler; args[1] is theapproximatestring). Note the WebGPU kernel additionally implements the exact/erf path, which the Vulkan handler does not currently support.Constraints — fp32 only (both operands must be 4-byte aligned, enforced in the handler); input and output must have identical byte size; 1D dispatch only (throws if the workgroup count would exceed the 65535 cap). Element count need not be a multiple of 4 (scalar tail); static shape (no resize hook).
Co-authored-with: Claude Code.
@exported-using-ghexport
Differential Revision: D110836674
Differential Revision: D110836674