[clang] [clang][Modules] Handle relocated modules during implicit module builds (PR #181836)

[Jan Svoboda via cfe-commits]

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@@ -3158,6 +3158,49 @@ ASTReader::ASTReadResult ASTReader::ReadOptionsBlock(
   }
 }
 
+ASTReader::RelocationCheckResult
+ASTReader::checkIfModuleRelocated(ModuleFile &F, bool DirectoryCheck) {
+  // Don't emit module relocation errors if we have -fno-validate-pch.
+  const bool IgnoreError =
+      bool(PP.getPreprocessorOpts().DisablePCHOrModuleValidation &
+           DisableValidationForModuleKind::Module);
+
+  if (!PP.getPreprocessorOpts().ModulesCheckRelocated)
+    return {std::nullopt, IgnoreError};
+
+  const bool IsImplicitModule = F.Kind == MK_ImplicitModule;
+
+  if (!DirectoryCheck &&
+      (!IsImplicitModule || ModuleMgr.begin()->Kind == MK_MainFile))
+    return {std::nullopt, IgnoreError};
+
+  const HeaderSearchOptions &HSOpts =
+      PP.getHeaderSearchInfo().getHeaderSearchOpts();
+
+  // When only validating modules once per build session,
+  // Skip check if the timestamp is up to date or module was built in same build
+  // session.
+  if (HSOpts.ModulesValidateOncePerBuildSession && IsImplicitModule) {
+    if (F.InputFilesValidationTimestamp >= HSOpts.BuildSessionTimestamp)
+      return {std::nullopt, IgnoreError};
+    if (static_cast<uint64_t>(F.File.getModificationTime()) >=
+        HSOpts.BuildSessionTimestamp)
+      return {std::nullopt, IgnoreError};
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jansvoboda11 wrote:

Why is this necessary? If the PCM got written in this build session, the timestamp got written as well, so this should be dead code.

https://github.com/llvm/llvm-project/pull/181836