[clang] Implement `-dump-minimization-hints` flag. (PR #133910)

[Viktoriia Bakalova via cfe-commits]

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@@ -49,6 +54,185 @@ LLVM_INSTANTIATE_REGISTRY(FrontendPluginRegistry)
 
 namespace {
 
+/// DeserializedDeclsLineRangePrinter dumps ranges of deserialized declarations
+/// to aid debugging and bug minimization. It implements ASTConsumer and
+/// ASTDeserializationListener, so that an object of
+/// DeserializedDeclsLineRangePrinter registers as its own listener. The
+/// ASTDeserializationListener interface provides the DeclRead callback that we
+/// use to collect the deserialized Decls. Note that printing or otherwise
+/// processing them as this point is dangerous, since that could trigger
+/// additional deserialization and crash compilation. Therefore, we process the
+/// collected Decls in HandleTranslationUnit method of ASTConsumer. This is a
+/// safe point, since we know that by this point all the Decls needed by the
+/// compiler frontend have been deserialized. In case our processing causes
+/// further deserialization, DeclRead from the listener might be called again.
+/// However, at that point we don't accept any more Decls for processing.
+class DeserializedDeclsLineRangePrinter : public ASTConsumer,
+                                          ASTDeserializationListener {
+public:
+  explicit DeserializedDeclsLineRangePrinter(
+      SourceManager &SM, std::unique_ptr<llvm::raw_fd_ostream> OS)
+      : ASTDeserializationListener(), SM(SM), OS(std::move(OS)) {}
+
+  ASTDeserializationListener *GetASTDeserializationListener() override {
+    return this;
+  }
+
+  void DeclRead(GlobalDeclID ID, const Decl *D) override {
+    if (!IsCollectingDecls)
+      return;
+    if (!D || isa<TranslationUnitDecl>(D) || isa<LinkageSpecDecl>(D) ||
+        isa<NamespaceDecl>(D)) {
+      // These decls cover a lot of nested declarations that might not be used,
+      // reducing the granularity and making the output less useful.
+      return;
+    }
+    if (auto *DC = D->getDeclContext(); !DC || !DC->isFileContext()) {
+      // We choose to work at namespace level to reduce complexity and the
+      // number of cases we care about.
+      return;
+    }
+    PendingDecls.push_back(D);
+  }
+
+  struct Position {
+    unsigned Line;
+    unsigned Column;
+
+    bool operator<(const Position &other) const {
+      if (Line < other.Line)
+        return true;
+      if (Line > other.Line)
+        return false;
+      return Column < other.Column;
+    }
+
+    static Position GetBeginSpelling(const SourceManager &SM,
+                                     const CharSourceRange &R) {
+      SourceLocation Begin = R.getBegin();
+      return {SM.getSpellingLineNumber(Begin),
+              SM.getSpellingColumnNumber(Begin)};
+    }
+
+    static Position GetEndSpelling(const SourceManager &SM,
+                                   const CharSourceRange &Range,
+                                   const LangOptions &LangOpts) {
+      // For token ranges, compute end location for end character of the range.
+      // The end location of returned range is exclusive.
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VitaNuo wrote:

Sure, I have modified the comment to say that column number (rather than end location) is exclusive. 

https://github.com/llvm/llvm-project/pull/133910