[clang] [clang][modules] Avoid calling expensive `SourceManager::translateFile()` (PR #86216)

[Ben Langmuir via cfe-commits]

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@@ -1337,9 +1337,24 @@ static bool compileModule(CompilerInstance &ImportingInstance,
   // Get or create the module map that we'll use to build this module.
   ModuleMap &ModMap
     = ImportingInstance.getPreprocessor().getHeaderSearchInfo().getModuleMap();
+  SourceManager &SourceMgr = ImportingInstance.getSourceManager();
   bool Result;
-  if (OptionalFileEntryRef ModuleMapFile =
-          ModMap.getContainingModuleMapFile(Module)) {
+  if (FileID ModuleMapFID = ModMap.getContainingModuleMapFileID(Module);
+      ModuleMapFID.isValid()) {
+    // We want to use the top-level module map. If we don't, the compiling
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benlangmuir wrote:

What is the connection between this change and the rest of the commit?

https://github.com/llvm/llvm-project/pull/86216