[AArch64] Improve TargetParser API
The TargetParser depends heavily on a collection of macros and enums to tie
together information about architectures, CPUs and extensions. Over time this
has led to some pretty awkward API choices. For example, recently a custom
operator-- has been added to the enum, which effectively turns iteration into
a graph traversal and makes the ordering of the macro calls in the header
significant. More generally there is a lot of string <-> enum conversion
going on. I think this shows the extent to which the current data structures
are constraining us, and the need for a rethink.
Key changes:
- Get rid of Arch enum, which is used to bind fields together. Instead of
passing around ArchKind, use the named ArchInfo objects directly or via
references.
- The list of all known ArchInfo becomes an array of pointers.
- ArchKind::operator-- is replaced with ArchInfo::implies(), which defines
which architectures are predecessors to each other. This allows features
from predecessor architectures to be added in a more intuitive way.
- Free functions of the form f(ArchKind) are converted to ArchInfo::f(). Some
functions become unnecessary and are deleted.
- Version number and profile are added to the ArchInfo. This makes comparison
of architectures easier and moves a couple of functions out of clang and
into AArch64TargetParser.
- clang::AArch64TargetInfo ArchInfo is initialised to Armv8a not INVALID.
- AArch64::ArchProfile which is distinct from ARM::ArchProfile
- Give things sensible names and add some comments.
Differential Revision: https://reviews.llvm.org/D138792