[SYCL][HIP] Implement buffered printf for the AMD backend#22676
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zjin-lcf wants to merge 1 commit into
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[SYCL][HIP] Implement buffered printf for the AMD backend#22676zjin-lcf wants to merge 1 commit into
zjin-lcf wants to merge 1 commit into
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SYCL device code on AMDGPU emitted calls to `printf` that were never lowered to a working runtime scheme, so experimental::printf produced no output (or crashed) on HIP. Enable the buffered printf scheme, which is the one the ROCm HIP runtime allocates and parses automatically (via the hidden_printf_buffer implicit kernarg and the code object's printf metadata); the hostcall scheme is intentionally avoided as it depends on ROCm's hostcall service and PCIe atomics that the SYCL/UR HIP runtime does not set up. The lowering must happen after inlining: in SYCL, printf calls are wrapped in the experimental::printf helper, so the format string only becomes a resolvable constant (needed to identify %s arguments and emit the correct buffer layout) once the wrapper is inlined. Doing this in clang CodeGen mis-encodes %s and corrupts the host heap during parsing. Changes: - AMDGPUPrintfRuntimeBinding: when the module requests the buffered scheme, lower printf via the shared llvm::emitAMDGPUPrintfCall emitter (same layout as clang's HIP -mprintf-kind=buffered) instead of the legacy OpenCL layout. This pass runs late, after inlining. - CodeGenModule: set the amdgpu_printf_kind="buffered" module flag for SYCL AMDGPU device code. - libclc: provide __printf_alloc for the libspirv AMDGPU target and mark it used so it survives internalization/DCE until the backend pass introduces the reference. - sycl-post-link: treat printf as a builtin to avoid a spurious "Undefined function printf" warning. - Re-enable the Printf/* and DeviceLib/built-ins/printf e2e tests on target-amd (issue 22300). Co-authored-by: Cursor <cursoragent@cursor.com>
wenju-he
reviewed
Jul 20, 2026
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| IRBuilder<> Builder(Head); | ||
| Builder.SetCurrentDebugLocation(CI->getDebugLoc()); | ||
| Value *Result = emitAMDGPUPrintfCall(Builder, Args, /*IsBuffered=*/true); |
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should the call be emitted by frontend? See https://github.com/ROCm/llvm-project/blob/54b9268abd943edc4d359428554d32bf22a94d68/clang/lib/CodeGen/CGGPUBuiltin.cpp#L192
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Summary
printffor the SYCL HIP (AMD) backend, replacing the unsupported hostcall scheme.AMDGPUPrintfRuntimeBindingviaemitAMDGPUPrintfCall, selected by anamdgpu_printf_kind="buffered"module flag set for SYCL AMDGPU device code (lowering after inlining so format strings are constant).__printf_allocin libspirv (__attribute__((used))) so it survives DCE until the backend pass needs it; suppress the spurioussycl-post-link"Undefined function printf" warning.Printf/*andDeviceLib/built-ins/printfe2e tests on HIP.Test plan
Printf/{char,double,float,int,mixed-address-space,percent-symbol}pass on gfx942DeviceLib/built-ins/printfpasses on gfx942Relates to #22300