This is phase-1 of switching from llvm::Optional to std::optional in the
next rebranch. llvm::Optional was removed from upstream LLVM, so we need
to migrate off rather soon. On Darwin, std::optional, and llvm::Optional
have the same layout, so we don't need to be as concerned about ABI
beyond the name mangling. `llvm::Optional` is only returned from one
function in
```
getStandardTypeSubst(StringRef TypeName,
bool allowConcurrencyManglings);
```
It's the return value, so it should not impact the mangling of the
function, and the layout is the same as `std::optional`, so it should be
mostly okay. This function doesn't appear to have users, and the ABI was
already broken 2 years ago for concurrency and no one seemed to notice
so this should be "okay".
I'm doing the migration incrementally so that folks working on main can
cherry-pick back to the release/5.9 branch. Once 5.9 is done and locked
away, then we can go through and finish the replacement. Since `None`
and `Optional` show up in contexts where they are not `llvm::None` and
`llvm::Optional`, I'm preparing the work now by going through and
removing the namespace unwrapping and making the `llvm` namespace
explicit. This should make it fairly mechanical to go through and
replace llvm::Optional with std::optional, and llvm::None with
std::nullopt. It's also a change that can be brought onto the
release/5.9 with minimal impact. This should be an NFC change.
When using a file list inputs to the swift-frontend invocation, the name
of the file is not significant, only the content of the file. Improve
cache key computation so only the content of the input file will affect
cache key, not the file name.
Teach swift how to serialize its input into CAS to create a cache key
for compiler outputs. To compute the cache key for the output, it first
needs to compute a base-key for the compiler invocation. The base key is
computed from: swift compiler version and the command-line arguments for
the invocation.
Each compiler output from swift will gets its own key. The key for the
output is computed from: the base key for the compiler invocation + the
primary input for the output + the output type.
