[Metal] Let compile callback declare payload format via (payload, fmt)#19924
[Metal] Let compile callback declare payload format via (payload, fmt)#19924echuraev wants to merge 1 commit into
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This pull request updates the Metal codegen build process to support a backward-compatible contract for the tvm_callback_metal_compile callback, allowing it to return either a compiled payload or a (payload, format) pair. It also adds corresponding unit tests to verify source passthrough and rejection of mixed formats. The feedback suggests correcting a minor typo ('Backwaard-compatible') in a comment within codegen_metal.cc.
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A tvm_callback_metal_compile used purely for debugging/inspection may return the MSL source unchanged. Previously, merely registering the callback forced the module format to "metallib", so the runtime tried to load the text source as a binary metallib and failed with "Invalid library file" (issue apache#18798). The callback may now return a (payload, format) pair to declare the payload format. A bare str/bytes return keeps the legacy metallib behavior. All kernels of a module share a single declared format, so a callback that mixes formats across kernels (including a legacy metallib return alongside a (payload, "metal") return) is rejected at codegen time instead of producing a module that fails to load.
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A tvm_callback_metal_compile used purely for debugging/inspection may return the MSL source unchanged. Previously, merely registering the callback forced the module format to "metallib", so the runtime tried to load the text source as a binary metallib and failed with "Invalid library file" (issue #18798).
The callback may now return a (payload, format) pair to declare the payload format. A bare str/bytes return keeps the legacy metallib behavior. All kernels of a module share a single declared format, so a callback that mixes formats across kernels (including a legacy metallib return alongside a (payload, "metal") return) is rejected at codegen time instead of producing a module that fails to load.