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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/WritingAnLLVMBackend.rst | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/docs/WritingAnLLVMBackend.rst b/docs/WritingAnLLVMBackend.rst index a03a5e4..9e3cb9e 100644 --- a/docs/WritingAnLLVMBackend.rst +++ b/docs/WritingAnLLVMBackend.rst @@ -911,6 +911,47 @@ format instructions will bind the operands to the ``rd``, ``rs1``, and ``rs2`` fields. This results in the ``XNORrr`` instruction binding ``$dst``, ``$b``, and ``$c`` operands to the ``rd``, ``rs1``, and ``rs2`` fields respectively. +TableGen will also generate a function called getNamedOperandIdx() which +can be used to look up an operand's index in a MachineInstr based on its +TableGen name. Setting the UseNamedOperandTable bit in an instruction's +TableGen definition will add all of its operands to an enumeration in the +llvm::XXX:OpName namespace and also add an entry for it into the OperandMap +table, which can be queried using getNamedOperandIdx() + +.. code-block:: llvm + + int DstIndex = SP::getNamedOperandIdx(SP::XNORrr, SP::OpName::dst); // => 0 + int BIndex = SP::getNamedOperandIdx(SP::XNORrr, SP::OpName::b); // => 1 + int CIndex = SP::getNamedOperandIdx(SP::XNORrr, SP::OpName::c); // => 2 + int DIndex = SP::getNamedOperandIdx(SP::XNORrr, SP::OpName::d); // => -1 + + ... + +The entries in the OpName enum are taken verbatim from the TableGen definitions, +so operands with lowercase names will have lower case entries in the enum. + +To include the getNamedOperandIdx() function in your backend, you will need +to define a few preprocessor macros in XXXInstrInfo.cpp and XXXInstrInfo.h. +For example: + +XXXInstrInfo.cpp: + +.. code-block:: c++ + + #define GET_INSTRINFO_NAMED_OPS // For getNamedOperandIdx() function + #include "XXXGenInstrInfo.inc" + +XXXInstrInfo.h: + +.. code-block:: c++ + + #define GET_INSTRINFO_OPERAND_ENUM // For OpName enum + #include "XXXGenInstrInfo.inc" + + namespace XXX { + int16_t getNamedOperandIdx(uint16_t Opcode, uint16_t NamedIndex); + } // End namespace XXX + Instruction Relation Mapping ---------------------------- |