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

Currently the decoder and encoder emitters will crash if DefaultMode is
used within an EncodingByHwMode. As can be done today for
RegInfoByHwMode and ValueTypeByHwMode, this patch adds support for this
usage in EncodingByHwMode:
  let EncodingInfos =
    EncodingByHwMode<[ModeA, DefaultMode], [EncA, EncDefault]>;

Currently the DecoderEmitter spends a fair amount of cycles performing
repeated linear walks over the entire instruction list. This patch
eliminates one such walk during HwMode collection for EncodingInfos.

The eliminated traversal visits every instruction and then every
EncodingInfos entry for that instruction merely to collect all
referenced HwModes. That information already happens to be present in
the HwModeSelects created during the one-time construction of
CodeGenHwModes. We instead traverse the HwModeSelects, collecting each
one referenced as an encoding select. This set is a small constant in
size and does not generally grow with the size of the instruction set.

```
find llvm/utils/TableGen -iname "*.h" -o -iname "*.cpp" | xargs clang-format-16 -i
```

Split from #80847

Use the predicate condition instead of checkFeatures in *GenDAGISel.inc.

This makes the code similar to isel pattern predicates.

checkFeatures is still used by code created by SubtargetEmitter so
we can't remove the string. Backends need to be careful to keep
the string and predicates in sync, but I don't think that's a big issue.

I haven't measured it, but this should be a compile time improvement
for isel since we don't have to do any of the string processing that's
inside checkFeatures.

Reviewed By: kparzysz

Differential Revision: https://reviews.llvm.org/D146012

We can use the Record* to uniquely identify the Record without using
its name.

Depending on the OS used, a module-enabled build can fail due to the
special handling <cassert> gets as textual header.

to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636

This replaces TableGen's type inference to operate on parameterized
types instead of MVTs, and as a consequence, some interfaces have
changed:
- Uses of MVTs are replaced by ValueTypeByHwMode.
- EEVT::TypeSet is replaced by TypeSetByHwMode.

This affects the way that types and type sets are printed, and the
tests relying on that have been updated.

There are certain users of the inferred types outside of TableGen
itself, namely FastISel and GlobalISel. For those users, the way
that the types are accessed have changed. For typical scenarios,
these replacements can be used:
- TreePatternNode::getType(ResNo) -> getSimpleType(ResNo)
- TreePatternNode::hasTypeSet(ResNo) -> hasConcreteType(ResNo)
- TypeSet::isConcrete -> TypeSetByHwMode::isValueTypeByHwMode(false)

For more information, please refer to the review page.

Differential Revision: https://reviews.llvm.org/D31951

llvm-svn: 313271