Support this cast to base class. (#4989)

Support this cast to base class.

Copy will be generated from this to tmp base class ptr.

tools/clang/lib/CodeGen/CGExprAgg.cpp

@@ -745,6 +745,8 @@ void AggExprEmitter::VisitCastExpr(CastExpr *E) {
           LV = CGF.EmitLValue(ArraySubExpr);
         else if (ParenExpr *parenExpr = dyn_cast<ParenExpr>(Src))
           LV = CGF.EmitLValue(parenExpr->getSubExpr());
+        else if (isa<CXXThisExpr>(Src))
+          LV = CGF.EmitLValue(Src);
         else
           LV = CGF.EmitAggExprToLValue(Src);
 

tools/clang/test/HLSLFileCheck/hlsl/classes/this_cast_to_base_class.hlsl

@@ -0,0 +1,93 @@
+// RUN: %dxc -T lib_6_6 -HV 2021 -disable-lifetime-markers -fcgl %s | FileCheck %s
+
+// CHECK-LABLE: define linkonce_odr void @"\01?foo@Child@@QAAXXZ"(%class.Child* %this)
+// CHECK: %[[OutArg:.+]] = alloca %class.Parent
+// CHECK: %[[OutThisPtr:.+]] = getelementptr inbounds %class.Child, %class.Child* %this, i32 0, i32 0
+// CHECK: call void @"\01?lib_func2@@YAXVParent@@@Z"(%class.Parent* %[[OutArg]])
+// Make sure copy-out.
+// CHECK: %[[OutThisCpyPtr:.+]] = bitcast %class.Parent* %[[OutThisPtr]] to i8*
+// CHECK: %[[OutArgCpyPtr:.+]] = bitcast %class.Parent* %[[OutArg]] to i8*
+// CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %[[OutThisCpyPtr]], i8* %[[OutArgCpyPtr]], i64 8, i32 1, i1 false)
+
+// CHECK-LABLE: define linkonce_odr void @"\01?bar@Child@@QAAXXZ"(%class.Child* %this)
+// CHECK: %[[InOutArg:.+]] = alloca %class.Parent
+// CHECK: %[[InOutThisPtr:.+]] = getelementptr inbounds %class.Child, %class.Child* %this, i32 0, i32 0
+
+// Make sure copy-in.
+// CHECK: %[[InOutArgCpyPtr:.+]] = bitcast %class.Parent* %[[InOutArg]] to i8*
+// CHECK: %[[InOutThisCpyPtr:.+]] = bitcast %class.Parent* %[[InOutThisPtr]] to i8*
+// CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %[[InOutArgCpyPtr]], i8* %[[InOutThisCpyPtr]], i64 8, i32 1, i1 false)
+
+// The call.
+// CHECK: call void @"\01?lib_func3@@YAXVParent@@@Z"(%class.Parent* %[[InOutArg]])
+
+// Make sure copy-out.
+// CHECK: %[[InOutThisCpyOutPtr:.+]] = bitcast %class.Parent* %[[InOutThisPtr]] to i8*
+// CHECK: %[[InOutArgCpyOutPtr:.+]] = bitcast %class.Parent* %[[InOutArg]] to i8*
+// CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %[[InOutThisCpyOutPtr]], i8* %[[InOutArgCpyOutPtr]], i64 8, i32 1, i1 false)
+
+
+// CHECK-LABLE: define linkonce_odr i32 @"\01?foo@Child@@QAAHHH@Z"(%class.Child* %this, i32 %a, i32 %b)
+// CHECK: %[[Arg:.+]] = alloca %class.Parent
+// CHECK: %[[Tmp:.+]] = alloca %class.Parent, align 4
+
+// Make sure this is copy to agg tmp.
+// CHECK: %[[PtrI:.+]] = getelementptr inbounds %class.Child, %class.Child* %this, i32 0, i32 0, i32 0
+// CHECK: %[[PtrJ:.+]] = getelementptr inbounds %class.Child, %class.Child* %this, i32 0, i32 0, i32 1
+// CHECK: %[[I:.+]] = load i32, i32* %[[PtrI]]
+// CHECK: %[[J:.+]] = load float, float* %[[PtrJ]]
+// CHECK: %[[TmpPtrI:.+]] = getelementptr inbounds %class.Parent, %class.Parent* %[[Tmp]], i32 0, i32 0
+// CHECK: %[[TmpPtrJ:.+]] = getelementptr inbounds %class.Parent, %class.Parent* %[[Tmp]], i32 0, i32 1
+// CHECK: store i32 %[[I]], i32* %[[TmpPtrI]]
+// CHECK: store float %[[J]], float* %[[TmpPtrJ]]
+
+// Make sure Tmp copy to Arg.
+// CHECK: %[[ArgPtr:.+]] = bitcast %class.Parent* %[[Arg]] to i8*
+// CHECK: %[[TmpPtr:.+]] = bitcast %class.Parent* %[[Tmp]] to i8*
+// CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %[[ArgPtr]], i8* %[[TmpPtr]], i64 8, i32 1, i1 false)
+
+// Use Arg to call lib_func.
+// CHECK: call i32 @"\01?lib_func@@YAHVParent@@HH@Z"(%class.Parent* %[[Arg]], i32 %{{.*}}, i32 %{{.*}})
+
+class Parent
+{
+    int i;
+    float f;
+};
+
+int lib_func(Parent obj, int a, int b);
+void lib_func2(out Parent obj);
+void lib_func3(inout Parent obj);
+
+class Child : Parent
+{
+    int foo(int a, int b)
+    {
+        return lib_func(this, a, b);
+    }
+    void foo() {
+        lib_func2((Parent)this);
+    }
+    void bar() {
+        lib_func3((Parent)this);
+    }
+    double d;
+};
+
+#define RS \
+    "RootFlags(0), " \
+    "DescriptorTable(UAV(u0))"
+
+RWBuffer<uint> gOut : register(u0);
+
+[shader("compute")]
+[RootSignature(RS)]
+[numthreads(1, 1, 1)]
+void main(uint3 DTid : SV_DispatchThreadID)
+{
+    Child c;
+    c.i = 110;
+    c.foo();
+    c.bar();
+    gOut[0] = c.foo(111, 112);
+}