[clang] [clang] Optimize castToDeclContext for 2% improvement in build times (PR #76825)

[Vlad Serebrennikov via cfe-commits]

================
@@ -210,38 +253,26 @@ void clang::EmitClangDeclContext(RecordKeeper &Records, raw_ostream &OS) {
   OS << "#ifndef DECL_CONTEXT\n";
   OS << "#  define DECL_CONTEXT(DECL)\n";
   OS << "#endif\n";
-  
-  OS << "#ifndef DECL_CONTEXT_BASE\n";
-  OS << "#  define DECL_CONTEXT_BASE(DECL) DECL_CONTEXT(DECL)\n";
-  OS << "#endif\n";
-  
-  typedef std::set<Record*> RecordSet;
-  typedef std::vector<Record*> RecordVector;
-  
-  RecordVector DeclContextsVector
-    = Records.getAllDerivedDefinitions(DeclContextNodeClassName);
-  RecordVector Decls = Records.getAllDerivedDefinitions(DeclNodeClassName);
-  RecordSet DeclContexts (DeclContextsVector.begin(), DeclContextsVector.end());
-   
-  for (RecordVector::iterator i = Decls.begin(), e = Decls.end(); i != e; ++i) {
-    Record *R = *i;
-
-    if (Record *B = R->getValueAsOptionalDef(BaseFieldName)) {
-      if (DeclContexts.find(B) != DeclContexts.end()) {
-        OS << "DECL_CONTEXT_BASE(" << B->getName() << ")\n";
-        DeclContexts.erase(B);
-      }
-    }
+
+  std::vector<Record *> DeclContextsVector =
+      Records.getAllDerivedDefinitions(DeclContextNodeClassName);
+  std::vector<Record *> Decls =
+      Records.getAllDerivedDefinitions(DeclNodeClassName);
+
+  std::multimap<Record *, Record *> Tree;
+
+  const std::vector<Record *> Stmts =
+      Records.getAllDerivedDefinitions(DeclNodeClassName);
+
+  for (unsigned i = 0, e = Stmts.size(); i != e; ++i) {
----------------
Endilll wrote:

Is there a reason to avoid range-based `for` loop here?

https://github.com/llvm/llvm-project/pull/76825