[Support] Remove output file checks from LockFileManager

clang/lib/Frontend/CompilerInstance.cpp

@@ -1406,7 +1406,7 @@ static bool readASTAfterCompileModule(CompilerInstance &ImportingInstance,
                                       SourceLocation ImportLoc,
                                       SourceLocation ModuleNameLoc,
                                       Module *Module, StringRef ModuleFileName,
-                                      bool *OutOfDate) {
+                                      bool *OutOfDate, bool *Missing) {
   DiagnosticsEngine &Diags = ImportingInstance.getDiagnostics();
 
   unsigned ModuleLoadCapabilities = ASTReader::ARR_Missing;
@@ -1427,6 +1427,12 @@ static bool readASTAfterCompileModule(CompilerInstance &ImportingInstance,
     return false;
   }
 
+  // The caller wants to handle missing module files.
+  if (Missing && ReadResult == ASTReader::Missing) {
+    *Missing = true;
+    return false;
+  }
+
   // The ASTReader didn't diagnose the error, so conservatively report it.
   if (ReadResult == ASTReader::Missing || !Diags.hasErrorOccurred())
     Diags.Report(ModuleNameLoc, diag::err_module_not_built)
@@ -1452,7 +1458,7 @@ static bool compileModuleAndReadASTImpl(CompilerInstance &ImportingInstance,
 
   return readASTAfterCompileModule(ImportingInstance, ImportLoc, ModuleNameLoc,
                                    Module, ModuleFileName,
-                                   /*OutOfDate=*/nullptr);
+                                   /*OutOfDate=*/nullptr, /*Missing=*/nullptr);
 }
 
 /// Compile a module in a separate compiler instance and read the AST,
@@ -1517,15 +1523,17 @@ static bool compileModuleAndReadASTBehindLock(
 
     // Read the module that was just written by someone else.
     bool OutOfDate = false;
+    bool Missing = false;
     if (readASTAfterCompileModule(ImportingInstance, ImportLoc, ModuleNameLoc,
-                                  Module, ModuleFileName, &OutOfDate))
+                                  Module, ModuleFileName, &OutOfDate, &Missing))
       return true;
-    if (!OutOfDate)
+    if (!OutOfDate && !Missing)
       return false;
 
-    // The module may be out of date in the presence of file system races,
-    // or if one of its imports depends on header search paths that are not
-    // consistent with this ImportingInstance.  Try again...
+    // The module may be missing or out of date in the presence of file system
+    // races. It may also be out of date if one of its imports depends on header
+    // search paths that are not consistent with this ImportingInstance.
+    // Try again...
   }
 }
 

llvm/include/llvm/Support/LockFileManager.h

@@ -16,14 +16,13 @@
 namespace llvm {
 class StringRef;
 
-/// Class that manages the creation of a lock file to aid
-/// implicit coordination between different processes.
+/// Class that manages the creation of a lock file to aid implicit coordination
+/// between different processes.
 ///
-/// The implicit coordination works by creating a ".lock" file alongside
-/// the file that we're coordinating for, using the atomicity of the file
-/// system to ensure that only a single process can create that ".lock" file.
-/// When the lock file is removed, the owning process has finished the
-/// operation.
+/// The implicit coordination works by creating a ".lock" file, using the
+/// atomicity of the file system to ensure that only a single process can create
+/// that ".lock" file. When the lock file is removed, the owning process has
+/// finished the operation.
 class LockFileManager {
 public:
   /// Describes the state of a lock file.

llvm/lib/Support/LockFileManager.cpp

@@ -307,12 +307,8 @@ LockFileManager::waitForUnlock(const unsigned MaxSeconds) {
   while (Backoff.waitForNextAttempt()) {
     // FIXME: implement event-based waiting
     if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
-        errc::no_such_file_or_directory) {
-      // If the original file wasn't created, somone thought the lock was dead.
-      if (!sys::fs::exists(FileName))
-        return Res_OwnerDied;
+        errc::no_such_file_or_directory)
       return Res_Success;
-    }
 
     // If the process owning the lock died without cleaning up, just bail out.
     if (!processStillExecuting((*Owner).first, (*Owner).second))