Refactor of the llvm-tblgen source into:
- a "Basic" library, which contains the bare minimum utilities to build
`llvm-min-tablegen`
- a "Common" library which contains all of the helpers for TableGen
backends. Such helpers can be shared by more than one backend, and even
unit tested (e.g. CodeExpander is, maybe we can add more over time)
Fixes#80647
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;
}
```
