If the second instruction is commutable, we should be able to check
its commutable operands.
A simple RISCV fusion is contained in this PR to show the functionality
is correct, I may remove it when landing.
Fixes#82738
`FusionPredicate` is used to predicate if target instruction matches
the requirement. The targets can be firstMI, secondMI or both.
The `Fusion` contains a list of `FusionPredicate`. The generated code
will be like:
```
bool isNAME(const TargetInstrInfo &TII,
const TargetSubtargetInfo &STI,
const MachineInstr *FirstMI,
const MachineInstr &SecondMI) {
auto &MRI = SecondMI.getMF()->getRegInfo();
/* Predicates */
return true;
}
```
A boilerplate class called `SimpleFusion` is added. `SimpleFusion` has
a predefined structure of predicates and accepts predicate for
`firstMI`, predicate for `secondMI` and epilog/prolog as arguments.
The generated code for `SimpleFusion` will be like:
```
bool isNAME(const TargetInstrInfo &TII,
const TargetSubtargetInfo &STI,
const MachineInstr *FirstMI,
const MachineInstr &SecondMI) {
auto &MRI = SecondMI.getMF()->getRegInfo();
/* Prolog */
/* Predicate for `SecondMI` */
/* Wildcard */
/* Predicate for `FirstMI` */
/* Check One Use */
/* Tie registers */
/* Epilog */
return true;
}
```
