Vulkan: conv2d_local_wg_size() classifies by shader name only, making its SlidingWindow branch unreachable

[msluszniak]

🐛 Describe the bug

conv2d_local_wg_size() in backends/vulkan/runtime/graph/ops/impl/Convolution.cpp classifies the convolution method by shader name only, and the condition it uses matches every conv2d shader. As a result its SlidingWindow branch is unreachable for all conv2d variants, and they all receive the pointwise local workgroup shape.

// conv2d_local_wg_size()
Conv2dMethod method;
if (shader.kernel_name.find("conv2d_pw") != std::string::npos ||
    (shader.kernel_name.find("conv2d") != std::string::npos &&
     shader.kernel_name.find("conv_transpose2d") == std::string::npos)) {
  method = Conv2dMethod::Pointwise;
} else {
  method = Conv2dMethod::SlidingWindow;
}

The sliding window shader is itself named conv2d, so it matches find("conv2d") != npos and is classified as Pointwise. The same applies to conv2d_dw. Only conv_transpose2d reaches the else, and it is labelled SlidingWindow.

The intent is visible in the sibling function directly above, conv2d_global_wg_size(), which uses the identical outer name test but then disambiguates properly by inspecting the weights:

const auto& weight_sizes = graph->get_tref(weight_data)->sizes;
if (weight_sizes.at(2) == 1 && weight_sizes.at(3) == 1) {
  method = Conv2dMethod::Pointwise;
} else {
  method = Conv2dMethod::SlidingWindow;
}

conv2d_local_wg_size() is missing that second step, so the two functions can disagree about the method for the same dispatch: the global size is computed as sliding window while the local size is computed as pointwise.

Impact

Every non-pointwise conv2d takes the {64 / local_wg_size_y, local_wg_size_y, 1} path intended for pointwise convolutions, instead of graph->create_local_wg_size(global_workgroup_size). For the shapes I checked the resulting local size works out to {8, 8, 1} either way, so I have not observed a correctness or performance difference. Filing it as a latent bug rather than an active one: the dead branch means any future change to the sliding window local size selection would silently have no effect.

Found while investigating #21938 and #21939. It is not the cause of either.

Versions

ExecuTorch 1.4.1, Vulkan backend, Adreno 840v2 (Galaxy S26 Ultra, SM-S948B).

cc @SS-JIA @manuelcandales @digantdesai @cbilgin