Cache additional TypeRefBuilder operations

[btroller]

Speed up Remote Mirror significantly by caching two additional calculations in TypeRefBuilder.

These changes shouldn't significantly impact the memory footprint of Remote Mirror. Testing against a large process which used plenty of Swift, I saw BuiltInTypeDescriptorCache contain only about 4000 entries, and NormalizedReflectionNameCache only cache 3 MB of strings.

Resolves rdar://111248508

[btroller]

@swift-ci Please test

[mikeash]

Looks great!

[mikeash]

It might be good to make this lazy. I don't think leaks et al will care, but swift-inspect has paths that would never use this info and might benefit. We don't have to do that now, though.

[btroller]

I'd be happy to do that in this PR.

Are you thinking something like this, using std::call_once()?

In TypeRefBuilder.h:

  ...
  /// Cache for built-in type descriptor lookups.
  std::unordered_map<std::string /* normalized name */,
                     RemoteRef<BuiltinTypeDescriptor>>
      BuiltInTypeDescriptorCache;

  /// Once flag for lazily initializing BuiltInTypeDescriptorCache.
  std::once_flag BuiltInTypeDescriptorCacheInitOnceFlag;
  ...

And in TypeRefBuilder.cpp:

...
RemoteRef<BuiltinTypeDescriptor>
TypeRefBuilder::getBuiltinTypeInfo(const TypeRef *TR) {
  ...
  std::call_once(BuiltInTypeDescriptorCacheInitOnceFlag, []() {
    for (auto Info : ReflectionInfos) {
      for (auto BuiltinTypeDescriptor : Info.Builtin) {
        < populate BuiltInTypeDescriptorCache >
      }
    }
  });

  if (const auto found = BuiltInTypeDescriptorCache.find(MangledName);
      found != BuiltInTypeDescriptorCache.end()) {
    return found->second;
  }

  return nullptr;
}
...

[mikeash]

I'm not sure if anything actually relies on this, but we'd want to keep the cache up to date when new reflection infos are added. I suggest tracking the index of the last reflection info that's been cached, like:

uint32_t NormalizedReflectionNameCacheLastReflectionInfoCached;

Then in getBuiltinTypeInfo:

for(; NormalizedReflectionNameCacheLastReflectionInfoCached < ReflectionInfos.size(); NormalizedReflectionNameCacheLastReflectionInfoCached++)
  ...cache ReflectionInfos[NormalizedReflectionNameCacheLastReflectionInfoCached]...
  ...

[btroller]

Ah, good point. I'll take a stab at that.

[btroller]

@swift-ci Please test

[btroller]

@swift-ci Please test