The anatomy of a MachineInstr instance

While working in the backend, you’ll mainly be manipulating MachineInstr instances. As such, it’s important to have a good understanding of what they represent and how to make sure what you’re doing with them is legal since what you do preserves the semantics of the program.

At a high level, a MachineInstr object is a combination of three things:

• An array of MachineOperand instances
• Some flags that can be set or queried – for instance, the fast-math flags attached to this instruction, whether it’s an instruction used for setting up the call frame, and so on (see the MachineInstr::getFlag/setFlag family of methods).
• Properties that allow the target independent passes to figure out the effects the instruction may have – for instance, the MachineInstr::mayLoad method returns true for instructions that can read from memory and the MachineInstr::isCommutable method returns true if...