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.
I tried to split this into smaller commits, but couldn't find a way to do it
without requiring people to review a lot of code that would be deleted in the
next patch.
AArch64 only for now, but if it is accepted I will work on the same for ARM.
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.