[REFACTOR][RUNTIME] Phase out include/tvm/runtime/builtin_fp16.h#19472
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The public header existed only to declare fp16 ABI symbols for compiler-side callers. support/scalars.cc was already phased out upstream; this commit migrates the lone remaining caller (cublas codegen) to the 3rdparty inline header (3rdparty/compiler-rt/builtin_fp16.h, already on the SYSTEM include path), then deletes the public header outright. The call site is updated to use the __extendXfYf2__ template directly (the 3rdparty header provides the template but not the __gnu_h2f_ieee wrapper by name). The TVM_RUNTIME_DLL symbols in src/runtime/builtin_fp16.cc are kept -- they are the JIT-fallback symbols loaded at runtime when libgcc/compiler-rt fp16 builtins are not linked in the host process. That purpose is now documented in a top-of-file comment. Also fixes a broken relative path in src/runtime/contrib/random/mt_random_engine.cc (was '../3rdparty/...' which resolves to a non-existent path; it compiled only because the SYSTEM include path covered it). Same pattern as the runtime/threading_backend.h phase-out (apache#19469).
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This pull request removes the public header include/tvm/runtime/builtin_fp16.h and updates internal components to use the compiler-rt version of builtin_fp16.h. It also adds documentation explaining the JIT-fallback rationale for fp16 symbols. Feedback indicates that the JIT-fallback implementation in src/runtime/builtin_fp16.cc may be incomplete, as it lacks exports for standard symbols like __truncsfhf2 and __extendhfsf2 which were previously available in the public header.
spectrometerHBH
approved these changes
Apr 29, 2026
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Summary
include/tvm/runtime/builtin_fp16.hhas been in the public include tree without serving a public-API purpose. The header declared fp16 ABI symbols (__gnu_f2h_ieee,__gnu_h2f_ieee, etc.) for compiler-side callers;support/scalars.ccwas already phased out upstream, and this PR migrates the lone remaining caller (src/relax/backend/contrib/cublas/codegen.cc) to the 3rdparty inline header (3rdparty/compiler-rt/builtin_fp16.h, already on the CMake SYSTEM include path), then deletes the public header outright.