[clang] [WIP][C++20][Modules] Lazily, but fully load 'HeaderFileInfo' table into memory. (PR #140867)

[Chuanqi Xu via cfe-commits]

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@@ -654,6 +654,10 @@ class ASTReader
   /// Map from the TU to its lexical contents from each module file.
   std::vector<std::pair<ModuleFile*, LexicalContents>> TULexicalDecls;
 
+  unsigned HeaderFileInfoIdx = 0;
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ChuanqiXu9 wrote:

And also, this seems unsafe since ModuleManager can remove modules technically. Maybe it is better to insert a bool in ModuleFile to mark if its header info is loaded. 

https://github.com/llvm/llvm-project/pull/140867