[ThinLTO] Add caching to the new LTO API
Add the ability to plug a cache on the LTO API.
I tried to write such that a linker implementation can
control the cache backend. This is intrusive and I'm
not totally happy with it, but I can't figure out a
better design right now.
Differential Revision: https://reviews.llvm.org/D23599
llvm-svn: 279576
diff --git a/llvm/lib/LTO/Caching.cpp b/llvm/lib/LTO/Caching.cpp
new file mode 100644
index 0000000..118efde
--- /dev/null
+++ b/llvm/lib/LTO/Caching.cpp
@@ -0,0 +1,104 @@
+//===-Caching.cpp - LLVM Link Time Optimizer Cache Handling ---------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Caching for ThinLTO.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/LTO/Caching.h"
+
+#ifdef HAVE_LLVM_REVISION
+#include "LLVMLTORevision.h"
+#endif
+
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+using namespace llvm::lto;
+
+static void commitEntry(StringRef TempFilename, StringRef EntryPath) {
+ // Rename to final destination (hopefully race condition won't matter here)
+ auto EC = sys::fs::rename(TempFilename, EntryPath);
+ if (EC) {
+ // Renaming failed, probably not the same filesystem, copy and delete.
+ {
+ auto ReloadedBufferOrErr = MemoryBuffer::getFile(TempFilename);
+ if (auto EC = ReloadedBufferOrErr.getError())
+ report_fatal_error(Twine("Failed to open temp file '") + TempFilename +
+ "': " + EC.message() + "\n");
+
+ raw_fd_ostream OS(EntryPath, EC, sys::fs::F_None);
+ if (EC)
+ report_fatal_error(Twine("Failed to open ") + EntryPath +
+ " to save cached entry\n");
+ // I'm not sure what are the guarantee if two processes are doing this
+ // at the same time.
+ OS << (*ReloadedBufferOrErr)->getBuffer();
+ }
+ sys::fs::remove(TempFilename);
+ }
+}
+
+CacheObjectOutput::~CacheObjectOutput() {
+ if (EntryPath.empty())
+ // The entry was never used by the client (tryLoadFromCache() wasn't called)
+ return;
+ // TempFilename is only set if getStream() was called, i.e. on cache miss when
+ // tryLoadFromCache() returned false. And EntryPath is valid if a Key was
+ // submitted, otherwise it has been set to CacheDirectoryPath in
+ // tryLoadFromCache.
+ if (!TempFilename.empty()) {
+ if (EntryPath == CacheDirectoryPath)
+ // The Key supplied to tryLoadFromCache was empty, do not commit the temp.
+ EntryPath = TempFilename;
+ else
+ // We commit the tempfile into the cache now, by moving it to EntryPath.
+ commitEntry(TempFilename, EntryPath);
+ }
+ // Load the entry from the cache now.
+ auto ReloadedBufferOrErr = MemoryBuffer::getFile(EntryPath);
+ if (auto EC = ReloadedBufferOrErr.getError())
+ report_fatal_error(Twine("Can't reload cached file '") + EntryPath + "': " +
+ EC.message() + "\n");
+
+ // Supply the resulting buffer to the user.
+ AddBuffer(std::move(*ReloadedBufferOrErr));
+}
+
+// Return an allocated stream for the output, or null in case of failure.
+std::unique_ptr<raw_pwrite_stream> CacheObjectOutput::getStream() {
+ assert(!EntryPath.empty() && "API Violation: client didn't call "
+ "tryLoadFromCache() before getStream()");
+ // Write to a temporary to avoid race condition
+ int TempFD;
+ std::error_code EC =
+ sys::fs::createTemporaryFile("Thin", "tmp.o", TempFD, TempFilename);
+ if (EC) {
+ errs() << "Error: " << EC.message() << "\n";
+ report_fatal_error("ThinLTO: Can't get a temporary file");
+ }
+ return llvm::make_unique<raw_fd_ostream>(TempFD, /* ShouldClose */ true);
+}
+
+// Try loading from a possible cache first, return true on cache hit.
+bool CacheObjectOutput::tryLoadFromCache(StringRef Key) {
+ assert(!CacheDirectoryPath.empty() &&
+ "CacheObjectOutput was initialized without a cache path");
+ if (Key.empty()) {
+ // Client didn't compute a valid key. EntryPath has been set to
+ // CacheDirectoryPath.
+ EntryPath = CacheDirectoryPath;
+ return false;
+ }
+ sys::path::append(EntryPath, CacheDirectoryPath, Key);
+ return sys::fs::exists(EntryPath);
+}