[GlobalISel] Refactor Combiner MatchData & Apply C++ Code Handling (#92239)

Combiners that use C++ code in their "apply" pattern only use that. They
never mix it with MIR patterns as that has little added value.

This patch restricts C++ apply code so that if C++ is used, we cannot
use MIR patterns or builtins with it. Adding this restriction allows us
to merge calls to match and apply C++ code together, which in turns
makes it so we can just have MatchData variables on the stack.

So before, we would have
```
  GIM_CheckCxxInsnPredicate // match
  GIM_CheckCxxInsnPredicate // apply
  GIR_Done
```
Alongside a massive C++ struct holding the MatchData of all rules
possible (which was a big space/perf issue).

Now we just have
```
GIR_DoneWithCustomAction
```

And the function being ran just does
```
unsigned SomeMatchData;
if (match(SomeMatchData))
  apply(SomeMatchData)
```

This approach solves multiple issues in one:
- MatchData handling is greatly simplified and more efficient, "don't
pay for what you don't use"
  - We reduce the size of the match table
- Calling C++ code has a certain overhead (we need a switch), and this
overhead is only paid once now.

Handling of C++ code inside PatFrags is unchanged though, that still
emits a `GIM_CheckCxxInsnPredicate`. This is completely fine as they
can't use MatchDatas.

0 files changed, 0 insertions, 0 deletions