llvm-project/mlir/docs/Dialects/emitc.md

The EmitC dialect allows to convert operations from other MLIR dialects to EmitC ops. Those can be translated to C/C++ via the Cpp emitter.

The following convention is followed:

• If template arguments are passed to an emitc.call operation, C++ is generated.
• If tensors are used, C++ is generated.
• If multiple return values are used within in a functions or an emitc.call operation, C++11 is required.
• If floating-point type template arguments are passed to an emitc.call operation, C++20 is required.
• Else the generated code is compatible with C99.

These restrictions are neither inherent to the EmitC dialect itself nor to the Cpp emitter and therefore need to be considered while implementing conversions.

After the conversion, C/C++ code can be emitted with mlir-translate. The tool supports translating MLIR to C/C++ by passing -mlir-to-cpp. Furthermore, code with variables declared at top can be generated by passing the additional argument -declare-variables-at-top.

Besides operations part of the EmitC dialect, the Cpp targets supports translating the following operations:

• 'std' Dialect
  • std.br
  • std.call
  • std.cond_br
  • std.constant
  • std.return
• 'scf' Dialect
  • scf.for
  • scf.if
  • scf.yield
• 'arith' Dialect
  • 'arith.constant'