Implementing the MachineInstrBuilder class

The MachineInstrBuilder class exposes a function called BuildMI(). This function is used to build machine instructions.

How to do it…

Machine instructions are created by using the BuildMI functions, located in the include/llvm/CodeGen/MachineInstrBuilder.h file. The BuildMI functions make it easy to build arbitrary machine instructions.

For example, you can use BuildMI in code snippets for the following purposes:

1. To create a DestReg = mov 42 (rendered in the x86 assembly as mov DestReg, 42) instruction:

   MachineInstr *MI = BuildMI(X86::MOV32ri, 1, DestReg).addImm(42);

2. To create the same instruction, but insert it at the end of a basic block:

   MachineBasicBlock &MBB = BuildMI(MBB, X86::MOV32ri, 1, DestReg).addImm(42);

3. To create the same instruction, but insert it before a specified iterator point:

   MachineBasicBlock::iterator MBBI = 
   BuildMI(MBB, MBBI, X86::MOV32ri, 1, DestReg).addImm(42)

4. To create a self-looping branch instruction:

   BuildMI(MBB, X86::JNE,...