Don't crash when generating code for __attribute__((naked)) member functions.

[jlebar]

Summary

Previously this crashed inside EmitThisParam(). There should be no
prelude for naked functions, so just skip the whole thing.

[majnemer]

The MSVC side also needs the same change.

[jlebar]

Add check to MicrosoftCXXABI.

[jlebar]

Aha, indeed. Thanks.

[jlebar]

David, are we good here?

[majnemer]

LGTM

lib/CodeGen/ItaniumCXXABI.cpp

ImplicitParamDecl *VTTDecl
       = ImplicitParamDecl::Create(Context, nullptr, MD->getLocation(),
                                   &Context.Idents.get("vtt"), T);
     Params.insert(Params.begin() + 1, VTTDecl);
     getStructorImplicitParamDecl(CGF) = VTTDecl;
   }
 }
 
 void ItaniumCXXABI::EmitInstanceFunctionProlog(CodeGenFunction &CGF) {
+  // Naked functions have no prolog.
+  if (CGF.CurFuncDecl->hasAttr<NakedAttr>())
+    return;
+
   /// Initialize the 'this' slot.
   EmitThisParam(CGF);
 
   /// Initialize the 'vtt' slot if needed.
   if (getStructorImplicitParamDecl(CGF)) {
     getStructorImplicitParamValue(CGF) = CGF.Builder.CreateLoad(
         CGF.GetAddrOfLocalVar(getStructorImplicitParamDecl(CGF)), "vtt");
   }

lib/CodeGen/MicrosoftCXXABI.cpp

llvm::Value *MicrosoftCXXABI::adjustThisParameterInVirtualFunctionPrologue(
   This = CGF.Builder.CreateBitCast(This, charPtrTy);
   assert(Adjustment.isPositive());
   This = CGF.Builder.CreateConstInBoundsGEP1_32(CGF.Int8Ty, This,
                                                 -Adjustment.getQuantity());
   return CGF.Builder.CreateBitCast(This, thisTy);
 }
 
 void MicrosoftCXXABI::EmitInstanceFunctionProlog(CodeGenFunction &CGF) {
+  // Naked functions have no prolog.
+  if (CGF.CurFuncDecl->hasAttr<NakedAttr>())
+    return;
+
   EmitThisParam(CGF);
 
   /// If this is a function that the ABI specifies returns 'this', initialize
   /// the return slot to 'this' at the start of the function.
   ///
   /// Unlike the setting of return types, this is done within the ABI
   /// implementation instead of by clients of CGCXXABI because:
   /// 1) getThisValue is currently protected

test/CodeGenCXX/naked.cpp

+// RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-windows -emit-llvm %s -o - | FileCheck %s
+
+class TestNaked {
+public:
+  void NakedFunction();
+};
+
+__attribute__((naked)) void TestNaked::NakedFunction() {
+  // CHECK-LABEL: define void @
+  // CHECK: call void asm sideeffect
+  asm("");
+}