[clang][modules] Introduce new `ModuleCache` interface (#131193)

This PR adds new `ModuleCache` interface to Clang's implicitly-built
modules machinery. The main motivation for this change is to create a
second implementation that uses a more efficient kind of
`llvm::AdvisoryLock` during dependency scanning.

In addition to the lock abstraction, the `ModuleCache` interface also
manages the existing `InMemoryModuleCache` instance. I found that
compared to keeping these separate/independent, the code is a bit
simpler now, since these are two tightly coupled concepts. I can
envision a more efficient implementation of the `InMemoryModuleCache`
for the single-process case too, which will be much easier to implement
with the current setup.

This is not intended to be a functional change.

1 files changed, 2 insertions, 3 deletions

diff --git a/clang/lib/Frontend/PrecompiledPreamble.cpp b/clang/lib/Frontend/PrecompiledPreamble.cpp
index d1bac09..49fa2e9 100644
--- a/clang/lib/Frontend/PrecompiledPreamble.cpp
+++ b/clang/lib/Frontend/PrecompiledPreamble.cpp
@@ -292,10 +292,9 @@ private:
 class PrecompilePreambleConsumer : public PCHGenerator {
 public:
   PrecompilePreambleConsumer(PrecompilePreambleAction &Action, Preprocessor &PP,
-                             InMemoryModuleCache &ModuleCache,
-                             StringRef isysroot,
+                             ModuleCache &ModCache, StringRef isysroot,
                              std::shared_ptr<PCHBuffer> Buffer)
-      : PCHGenerator(PP, ModuleCache, "", isysroot, std::move(Buffer),
+      : PCHGenerator(PP, ModCache, "", isysroot, std::move(Buffer),
                      ArrayRef<std::shared_ptr<ModuleFileExtension>>(),
                      /*AllowASTWithErrors=*/true),
         Action(Action) {}