[MSVC Compat] Correctly handle finallys nested within finallys

[majnemer]

Summary

We'd lose track of the parent CodeGenFunction, leading us to get
confused with regard to which function a nested finally belonged to.

[rnk]

lib/CodeGen/CGException.cpp

1679–1682

Let's have a new field for this. We don't want most of the behavior controlled by CurCodeDecl in the rest of CodeGen.

[majnemer]

• Address Reid's review comments

[rnk]

lgtm

lib/CodeGen/CGException.cpp

void CodeGenFunction::startOutlinedSEHHelper(CodeGenFunction &ParentCGF,
                                              bool IsFilter,
                                              const Stmt *OutlinedStmt) {
   SourceLocation StartLoc = OutlinedStmt->getLocStart();
 
   // Get the mangled function name.
   SmallString<128> Name;
   {
     llvm::raw_svector_ostream OS(Name);
-    const Decl *ParentCodeDecl = ParentCGF.CurCodeDecl;
-    const NamedDecl *Parent = dyn_cast_or_null<NamedDecl>(ParentCodeDecl);
-    assert(Parent && "FIXME: handle unnamed decls (lambdas, blocks) with SEH");
+    const FunctionDecl *ParentSEHFn = ParentCGF.CurSEHParent;
+    assert(ParentSEHFn && "No CurSEHParent!");
     MangleContext &Mangler = CGM.getCXXABI().getMangleContext();
     if (IsFilter)
-      Mangler.mangleSEHFilterExpression(Parent, OS);
+      Mangler.mangleSEHFilterExpression(ParentSEHFn, OS);
     else
-      Mangler.mangleSEHFinallyBlock(Parent, OS);
+      Mangler.mangleSEHFinallyBlock(ParentSEHFn, OS);
   }
 
   FunctionArgList Args;
   if (CGM.getTarget().getTriple().getArch() != llvm::Triple::x86 || !IsFilter) {
     // All SEH finally functions take two parameters. Win64 filters take two
     // parameters. Win32 filters take no parameters.
     if (IsFilter) {
       Args.push_back(ImplicitParamDecl::Create(
if (llvm::Comdat *C = ParentFn->getComdat()) {
     ParentFn->setComdat(C);
     Fn->setComdat(C);
   } else {
     Fn->setLinkage(llvm::GlobalValue::InternalLinkage);
   }
 
   IsOutlinedSEHHelper = true;
 
   StartFunction(GlobalDecl(), RetTy, Fn, FnInfo, Args,
                 OutlinedStmt->getLocStart(), OutlinedStmt->getLocStart());
+  CurSEHParent = ParentCGF.CurSEHParent;
 
   CGM.SetLLVMFunctionAttributes(nullptr, FnInfo, CurFn);
   EmitCapturedLocals(ParentCGF, OutlinedStmt, IsFilter);
 }
 
 /// Create a stub filter function that will ultimately hold the code of the
 /// filter expression. The EH preparation passes in LLVM will outline the code
 /// from the main function body into this stub.
 llvm::Function *

lib/CodeGen/CodeGenFunction.h

public:
 
   /// In ARC, whether we should autorelease the return value.
   bool AutoreleaseResult;
 
   /// Whether we processed a Microsoft-style asm block during CodeGen. These can
   /// potentially set the return value.
   bool SawAsmBlock;
 
+  const FunctionDecl *CurSEHParent = nullptr;
+
   /// True if the current function is an outlined SEH helper. This can be a
   /// finally block or filter expression.
   bool IsOutlinedSEHHelper;
 
   const CodeGen::CGBlockInfo *BlockInfo;
   llvm::Value *BlockPointer;
 
   llvm::DenseMap<const VarDecl *, FieldDecl *> LambdaCaptureFields;
llvm::BasicBlock *getUnreachableBlock() {
     return UnreachableBlock;
   }
 
   llvm::BasicBlock *getInvokeDest() {
     if (!EHStack.requiresLandingPad()) return nullptr;
     return getInvokeDestImpl();
   }
 
-  bool currentFunctionUsesSEHTry() const {
-    const auto *FD = dyn_cast_or_null<FunctionDecl>(CurCodeDecl);
-    return FD && FD->usesSEHTry();
-  }
+  bool currentFunctionUsesSEHTry() const { return CurSEHParent != nullptr; }
 
   const TargetInfo &getTarget() const { return Target; }
   llvm::LLVMContext &getLLVMContext() { return CGM.getLLVMContext(); }
 
   //===--------------------------------------------------------------------===//
   //                                  Cleanups
   //===--------------------------------------------------------------------===//
 

lib/CodeGen/CodeGenFunction.cpp

void CodeGenFunction::StartFunction(GlobalDecl GD,
                                     SourceLocation StartLoc) {
   assert(!CurFn &&
          "Do not use a CodeGenFunction object for more than one function");
 
   const Decl *D = GD.getDecl();
 
   DidCallStackSave = false;
   CurCodeDecl = D;
+  if (const auto *FD = dyn_cast_or_null<FunctionDecl>(D))
+    if (FD->usesSEHTry())
+      CurSEHParent = FD;
   CurFuncDecl = (D ? D->getNonClosureContext() : nullptr);
   FnRetTy = RetTy;
   CurFn = Fn;
   CurFnInfo = &FnInfo;
   assert(CurFn->isDeclaration() && "Function already has body?");
 
   if (CGM.isInSanitizerBlacklist(Fn, Loc))
     SanOpts.clear();

test/CodeGen/exceptions-seh-finally.c

 // CHECK: call void @"\01?fin$0@0@nested___finally___finally_with_eh_edge@@"({{.*}})
 // CHECK-NEXT: cleanupret from %[[outerpad]] unwind to caller
 
 // CHECK-LABEL: define internal void @"\01?fin$0@0@nested___finally___finally_with_eh_edge@@"({{.*}})
 // CHECK: ret void
 
 // CHECK-LABEL: define internal void @"\01?fin$1@0@nested___finally___finally_with_eh_edge@@"({{.*}})
 // CHECK: unreachable
+
+void finally_within_finally() {
+  __try {
+    might_crash();
+  } __finally {
+    __try {
+      might_crash();
+    } __finally {
+    }
+  }
+}
+
+// CHECK-LABEL: define void @finally_within_finally(
+// CHECK: invoke void @might_crash(
+
+// CHECK: call void @"\01?fin$0@0@finally_within_finally@@"(
+// CHECK: call void @"\01?fin$0@0@finally_within_finally@@"({{.*}}) [ "funclet"(
+
+// CHECK-LABEL: define internal void @"\01?fin$0@0@finally_within_finally@@"(
+// CHECK: invoke void @might_crash(
+
+// CHECK: call void @"\01?fin$1@0@finally_within_finally@@"(
+// CHECK: call void @"\01?fin$1@0@finally_within_finally@@"({{.*}}) [ "funclet"(
+
+// CHECK-LABEL: define internal void @"\01?fin$1@0@finally_within_finally@@"(