[Sema] Push and Pop Expression Evaluation Context Records at the start and end of function definitions

[leonardchan]

Summary

This patch creates a new context for every function definition we enter. Currently we do not push and pop on these, usually working off of the global context record added in the Sema constructor, which never gets popped.

Ideally this will be one of the first patches for pushing and popping records so that we operate less off the global Sema record. I tried doing this as @rsmith recommends in https://reviews.llvm.org/D49511?id=160892#inline-451745, but ended up running into many issues that would be better addressed accross multiple patches.

Parent of https://reviews.llvm.org/D49511 where we would like to check for noderef usage on each context.

[rsmith]

Thanks!

clang/lib/Sema/SemaDecl.cpp

13181–13182 ↗

(On Diff #172272)

Adding this pop before each return seems error-prone. Can you do this with an RAII object instead?

lib/Sema/SemaDecl.cpp

 }
 
 Decl *Sema::ActOnStartOfFunctionDef(Scope *FnBodyScope, Decl *D,
                                     SkipBodyInfo *SkipBody) {
   if (!D) {
     // Parsing the function declaration failed in some way. Push on a fake scope
     // anyway so we can try to parse the function body.
     PushFunctionScope();
+    PushExpressionEvaluationContext(ExprEvalContexts.back().Context);
     return D;
   }
 
   FunctionDecl *FD = nullptr;
 
   if (FunctionTemplateDecl *FunTmpl = dyn_cast<FunctionTemplateDecl>(D))
     FD = FunTmpl->getTemplatedDecl();
   else
     FD = cast<FunctionDecl>(D);
 
+  // Do not push if it is a lambda because one is already pushed when building
+  // the lambda in ActOnStartOfLambdaDefinition().
+  if (!isLambdaCallOperator(FD))
+    PushExpressionEvaluationContext(ExprEvalContexts.back().Context);
+
   // Check for defining attributes before the check for redefinition.
   if (const auto *Attr = FD->getAttr<AliasAttr>()) {
     Diag(Attr->getLocation(), diag::err_alias_is_definition) << FD << 0;
     FD->dropAttr<AliasAttr>();
     FD->setInvalidDecl();
   }
   if (const auto *Attr = FD->getAttr<IFuncAttr>()) {
     Diag(Attr->getLocation(), diag::err_alias_is_definition) << FD << 1;
else if (ObjCMethodDecl *MD = dyn_cast<ObjCMethodDecl>(Decl))
     MD->setHasSkippedBody();
   return Decl;
 }
 
 Decl *Sema::ActOnFinishFunctionBody(Decl *D, Stmt *BodyArg) {
   return ActOnFinishFunctionBody(D, BodyArg, false);
 }
 
+/// RAII object that pops an ExpressionEvaluationContext when exiting a function
+/// body.
+class ExitFunctionBodyRAII {
+public:
+  ExitFunctionBodyRAII(Sema &S, bool IsLambda) : S(S), IsLambda(IsLambda) {}
+  ~ExitFunctionBodyRAII() {
+    if (!IsLambda)
+      S.PopExpressionEvaluationContext();
+  }
+
+private:
+  Sema &S;
+  bool IsLambda = false;
+};
+
 Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
                                     bool IsInstantiation) {
   FunctionDecl *FD = dcl ? dcl->getAsFunction() : nullptr;
 
   sema::AnalysisBasedWarnings::Policy WP = AnalysisWarnings.getDefaultPolicy();
   sema::AnalysisBasedWarnings::Policy *ActivePolicy = nullptr;
 
   if (getLangOpts().CoroutinesTS && getCurFunction()->isCoroutine())
     CheckCompletedCoroutineBody(FD, Body);
 
+  // Do not call PopExpressionEvaluationContext() if it is a lambda because one
+  // is already popped when finishing the lambda in BuildLambdaExpr(). This is
+  // meant to pop the context added in ActOnStartOfFunctionDef().
+  ExitFunctionBodyRAII ExitRAII(*this, isLambdaCallOperator(FD));
+
   if (FD) {
     FD->setBody(Body);
     FD->setWillHaveBody(false);
 
     if (getLangOpts().CPlusPlus14) {
       if (!FD->isInvalidDecl() && Body && !FD->isDependentContext() &&
           FD->getReturnType()->isUndeducedType()) {
         // If the function has a deduced result type but contains no 'return'

lib/Sema/SemaDeclObjC.cpp

 }
 
 /// ActOnStartOfObjCMethodDef - This routine sets up parameters; invisible
 /// and user declared, in the method definition's AST.
 void Sema::ActOnStartOfObjCMethodDef(Scope *FnBodyScope, Decl *D) {
   assert((getCurMethodDecl() == nullptr) && "Methodparsing confused");
   ObjCMethodDecl *MDecl = dyn_cast_or_null<ObjCMethodDecl>(D);
 
+  PushExpressionEvaluationContext(ExprEvalContexts.back().Context);
+
   // If we don't have a valid method decl, simply return.
   if (!MDecl)
     return;
 
   QualType ResultType = MDecl->getReturnType();
   if (!ResultType->isDependentType() && !ResultType->isVoidType() &&
       !MDecl->isInvalidDecl() &&
       RequireCompleteType(MDecl->getLocation(), ResultType,

lib/Sema/SemaExpr.cpp

// Otherwise, merge the contexts together.
     Cleanup.mergeFrom(Rec.ParentCleanup);
     MaybeODRUseExprs.insert(Rec.SavedMaybeODRUseExprs.begin(),
                             Rec.SavedMaybeODRUseExprs.end());
   }
 
   // Pop the current expression evaluation context off the stack.
   ExprEvalContexts.pop_back();
 
-  if (!ExprEvalContexts.empty())
-    ExprEvalContexts.back().NumTypos += NumTypos;
-  else
-    assert(NumTypos == 0 && "There are outstanding typos after popping the "
-                            "last ExpressionEvaluationContextRecord");
+  // The global expression evaluation context record is never popped.
 }
 
 void Sema::DiscardCleanupsInEvaluationContext() {
   ExprCleanupObjects.erase(
          ExprCleanupObjects.begin() + ExprEvalContexts.back().NumCleanupObjects,
          ExprCleanupObjects.end());
   Cleanup.reset();
   MaybeODRUseExprs.clear();