[CodeGen] Implement isTriviallyRecursive with StmtVisitor instead of RecursiveASTVisitor

This code doesn't need to traverse types, lambdas, template arguments,
etc to detect trivial recursion. We can do a basic statement traversal
instead. This reduces the time spent compiling CodeGenModule.cpp, the
object file size (mostly reduced debug info), and the final executable
size by a small amount. I measured the exe mostly to check how much of
the overhead is from debug info, object file section headers, etc, vs
actual code.

metric   | before | after | diff
time (s) | 47.4   | 38.5  | -8.9
obj (kb) | 12888  | 12012 | -876
exe (kb) | 86072  | 85996 | -76

llvm-svn: 352232

clang/lib/CodeGen/CodeGenModule.cpp

@@ -33,6 +33,7 @@
 #include "clang/AST/Mangle.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/AST/StmtVisitor.h"
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/CodeGenOptions.h"
@@ -2281,35 +2282,36 @@ static bool HasNonDllImportDtor(QualType T) {
 }
 
 namespace {
-  struct FunctionIsDirectlyRecursive :
-    public RecursiveASTVisitor<FunctionIsDirectlyRecursive> {
+  struct FunctionIsDirectlyRecursive
+      : public ConstStmtVisitor<FunctionIsDirectlyRecursive, bool> {
     const StringRef Name;
     const Builtin::Context &BI;
-    bool Result;
-    FunctionIsDirectlyRecursive(StringRef N, const Builtin::Context &C) :
-      Name(N), BI(C), Result(false) {
-    }
-    typedef RecursiveASTVisitor<FunctionIsDirectlyRecursive> Base;
+    FunctionIsDirectlyRecursive(StringRef N, const Builtin::Context &C)
+        : Name(N), BI(C) {}
 
-    bool TraverseCallExpr(CallExpr *E) {
+    bool VisitCallExpr(const CallExpr *E) {
       const FunctionDecl *FD = E->getDirectCallee();
       if (!FD)
-        return true;
-      AsmLabelAttr *Attr = FD->getAttr<AsmLabelAttr>();
-      if (Attr && Name == Attr->getLabel()) {
-        Result = true;
         return false;
-      }
+      AsmLabelAttr *Attr = FD->getAttr<AsmLabelAttr>();
+      if (Attr && Name == Attr->getLabel())
+        return true;
       unsigned BuiltinID = FD->getBuiltinID();
       if (!BuiltinID || !BI.isLibFunction(BuiltinID))
-        return true;
+        return false;
       StringRef BuiltinName = BI.getName(BuiltinID);
       if (BuiltinName.startswith("__builtin_") &&
           Name == BuiltinName.slice(strlen("__builtin_"), StringRef::npos)) {
-        Result = true;
-        return false;
+        return true;
       }
-      return true;
+      return false;
+    }
+
+    bool VisitStmt(const Stmt *S) {
+      for (const Stmt *Child : S->children())
+        if (Child && this->Visit(Child))
+          return true;
+      return false;
     }
   };
 
@@ -2394,8 +2396,8 @@ CodeGenModule::isTriviallyRecursive(const FunctionDecl *FD) {
   }
 
   FunctionIsDirectlyRecursive Walker(Name, Context.BuiltinInfo);
-  Walker.TraverseFunctionDecl(const_cast<FunctionDecl*>(FD));
-  return Walker.Result;
+  const Stmt *Body = FD->getBody();
+  return Body ? Walker.Visit(Body) : false;
 }
 
 bool CodeGenModule::shouldEmitFunction(GlobalDecl GD) {