diff options
Diffstat (limited to 'llvm/docs/MIRLangRef.rst')
| -rw-r--r-- | llvm/docs/MIRLangRef.rst | 21 |
1 files changed, 19 insertions, 2 deletions
diff --git a/llvm/docs/MIRLangRef.rst b/llvm/docs/MIRLangRef.rst index d3c9f828bb3..a5f8c8c743a 100644 --- a/llvm/docs/MIRLangRef.rst +++ b/llvm/docs/MIRLangRef.rst @@ -380,7 +380,8 @@ Register Operands The :ref:`register <registers>` primitive is used to represent the register machine operands. The register operands can also have optional :ref:`register flags <register-flags>`, -a subregister index, and a reference to the tied register operand. +:ref:`a subregister index <subregister-indices>`, +and a reference to the tied register operand. The full syntax of a register operand is shown below: .. code-block:: llvm @@ -435,6 +436,23 @@ corresponding internal ``llvm::RegState`` representation: * - ``debug-use`` - ``RegState::Debug`` +.. _subregister-indices: + +Subregister Indices +~~~~~~~~~~~~~~~~~~~ + +The register machine operands can reference a portion of a register by using +the subregister indices. The example below shows an instance of the ``COPY`` +pseudo instruction that uses the X86 ``sub_8bit`` subregister index to copy 8 +lower bits from the 32-bit virtual register 0 to the 8-bit virtual register 1: + +.. code-block:: llvm + + %1 = COPY %0:sub_8bit + +The names of the subregister indices are target specific, and are typically +defined in the target's ``*RegisterInfo.td`` file. + Global Value Operands ^^^^^^^^^^^^^^^^^^^^^ @@ -458,7 +476,6 @@ the '@' prefix, like in the following examples: ``@0``, ``@989``. are missing. .. TODO: Describe the syntax for the bundled instructions. .. TODO: Describe the syntax for virtual register YAML definitions. -.. TODO: Describe the syntax of the subregisters. .. TODO: Describe the machine function's YAML flag attributes. .. TODO: Describe the syntax for the external symbol and register mask machine operands. |
