[clang] [clang][modules] Introduce a flag to keep redundant module lookups on relocation checks (PR #219107)

[Cyndy Ishida via cfe-commits]

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@@ -9133,6 +9133,11 @@ def fno_modules_check_relocated
       Group<f_Group>,
       HelpText<"Skip checks for relocated modules when loading PCM files">,
       MarshallingInfoNegativeFlag<PreprocessorOpts<"ModulesCheckRelocated">>;
+def fmodules_force_redundant_lookup
+    : Flag<["-"], "fmodules-force-redundant-lookup">,
+      Group<f_Group>,
+      HelpText<"Force redundant module lookup when loading PCM files">,
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cyndyishida wrote:

I used the same language as `fno_modules_check_relocated` for the help text. The high-level point is that when the compiler needs to load a PCM because it's used in a TU compilation, it also looks for that module via header search. The side effect (optimization?) part is on the search for that module, it can discover the presence of other modules.

I used this flag name to discourage its use, so I don't particularly mind that it raises these kinds of questions. 



https://github.com/llvm/llvm-project/pull/219107