[PATCH] D95628: WIP: clang-scan-deps: Skip the disk when scanning modules dependencies

[Duncan P. N. Exon Smith via Phabricator via cfe-commits]

dexonsmith created this revision.
dexonsmith added reviewers: Bigcheese, arphaman, sammccall.
Herald added subscribers: ributzka, tschuett.
dexonsmith requested review of this revision.
Herald added a project: clang.

Modules dependendency scanning builds lightweight modules (based on
minimized preprocess-only sources) in order to construct the module
dependency graph. Add `-intercept-module-outputs` (on-by-default), which
keeps these lightweight modules in memory instead of writing to and
reading from disk, leveraging llvm::vfs::OutputManager.

This patch uses a separate cache per worker, but these would ideally be
kept in a shared result cache (could be an in-memory CAS).

This is a WIP because it's based on the OutputManager RFC (see patches https://reviews.llvm.org/D95501 / https://reviews.llvm.org/D95502) but I'm posting this as well since it's a simple example usage.

I haven't benchmarked (yet); it's motivated by profiling from a couple of years ago that showed some slowdowns here.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D95628

Files:
  clang/include/clang/Tooling/DependencyScanning/DependencyScanningService.h
  clang/include/clang/Tooling/DependencyScanning/DependencyScanningWorker.h
  clang/lib/Tooling/DependencyScanning/DependencyScanningService.cpp
  clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp
  clang/tools/clang-scan-deps/ClangScanDeps.cpp

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