[modules] Add ability to specify module name to module file mapping (reapply)

Extend the -fmodule-file option to support the [<name>=]<file> value format.
If the name is omitted, then the old semantics is preserved (the module file
is loaded whether needed or not). If the name is specified, then the mapping
is treated as just another prebuilt module search mechanism, similar to
-fprebuilt-module-path, and the module file is only loaded if actually used
(e.g., via import). With one exception: this mapping also overrides module
file references embedded in other modules (which can be useful if module files
are moved/renamed as often happens during remote compilation).

This override semantics requires some extra work: we now store the module name
in addition to the file name in the serialized AST representation.

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D35020

llvm-svn: 312220

1 files changed, 14 insertions, 9 deletions

diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index 1ebcc0a..b18d273 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -128,21 +128,24 @@ void HeaderSearch::getHeaderMapFileNames(
     Names.push_back(HM.first->getName());
 }
 
-std::string HeaderSearch::getModuleFileName(Module *Module) {
+std::string HeaderSearch::getCachedModuleFileName(Module *Module) {
   const FileEntry *ModuleMap =
       getModuleMap().getModuleMapFileForUniquing(Module);
-  return getModuleFileName(Module->Name, ModuleMap->getName(),
-                           /*UsePrebuiltPath*/false);
+  return getCachedModuleFileName(Module->Name, ModuleMap->getName());
 }
 
-std::string HeaderSearch::getModuleFileName(StringRef ModuleName,
-                                            StringRef ModuleMapPath,
-                                            bool UsePrebuiltPath) {
-  if (UsePrebuiltPath) {
-    if (HSOpts->PrebuiltModulePaths.empty())
+std::string HeaderSearch::getPrebuiltModuleFileName(StringRef ModuleName,
+                                                    bool FileMapOnly) {
+  // First check the module name to pcm file map.
+  auto i (HSOpts->PrebuiltModuleFiles.find(ModuleName));
+  if (i != HSOpts->PrebuiltModuleFiles.end())
+    return i->second;
+
+  if (FileMapOnly || HSOpts->PrebuiltModulePaths.empty())
       return std::string();
 
-    // Go though each prebuilt module path and try to find the pcm file.
+  // Then go through each prebuilt module directory and try to find the pcm
+  // file.
     for (const std::string &Dir : HSOpts->PrebuiltModulePaths) {
       SmallString<256> Result(Dir);
       llvm::sys::fs::make_absolute(Result);
@@ -154,6 +157,8 @@ std::string HeaderSearch::getModuleFileName(StringRef ModuleName,
     return std::string();
   }
 
+std::string HeaderSearch::getCachedModuleFileName(StringRef ModuleName,
+                                                  StringRef ModuleMapPath) {
   // If we don't have a module cache path or aren't supposed to use one, we
   // can't do anything.
   if (getModuleCachePath().empty())