[CIR] Add support for null data member pointers (llvm#171945)

This adds the CIR support for handling null data member pointer values.

Author: andykaylor

clang/lib/CIR/CodeGen/CIRGenBuilder.h

@@ -194,6 +194,10 @@ class CIRGenBuilderTy : public cir::CIRBaseBuilderTy{
 returncir::DataMemberAttr::get(ty, memberIndex);
  }
 
+ cir::DataMemberAttr getNullDataMemberAttr(cir::DataMemberType ty){
+returncir::DataMemberAttr::get(ty);
+ }
+
 // Return true if the value is a null constant such as null pointer, (+0.0)
 // for floating-point or zero initializer
 boolisNullValue(mlir::Attribute attr) const{
@@ -360,6 +364,12 @@ class CIRGenBuilderTy : public cir::CIRBaseBuilderTy{
 returncir::IsFPClassOp::create(*this, loc, src, flags);
  }
 
+/// Create constant nullptr for pointer-to-data-member type ty.
+ cir::ConstantOp getNullDataMemberPtr(cir::DataMemberType ty,
+ mlir::Location loc){
+returncir::ConstantOp::create(*this, loc, getNullDataMemberAttr(ty));
+ }
+
 // TODO: split this to createFPExt/createFPTrunc when we have dedicated cast
 // operations.
  mlir::Value createFloatingCast(mlir::Value v, mlir::Type destType){

clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp

@@ -2210,6 +2210,23 @@ mlir::Value ScalarExprEmitter::VisitCastExpr(CastExpr *ce){
 return builder.getNullPtr(ty, cgf.getLoc(subExpr->getExprLoc()));
  }
 
+case CK_NullToMemberPointer:{
+if (mustVisitNullValue(subExpr))
+ cgf.emitIgnoredExpr(subExpr);
+
+assert(!cir::MissingFeatures::cxxABI());
+
+const MemberPointerType *mpt = ce->getType()->getAs<MemberPointerType>();
+if (mpt->isMemberFunctionPointerType()){
+ cgf.cgm.errorNYI(subExpr->getSourceRange(),
+"CK_NullToMemberPointer: member function pointer");
+return{};
+ }
+
+auto ty = mlir::cast<cir::DataMemberType>(cgf.convertType(destTy));
+return builder.getNullDataMemberPtr(ty, cgf.getLoc(subExpr->getExprLoc()));
+ }
+
 case CK_LValueToRValue:
 assert(cgf.getContext().hasSameUnqualifiedType(subExpr->getType(), destTy));
 assert(subExpr->isGLValue() && "lvalue-to-rvalue applied to r-value!");

clang/test/CIR/CodeGen/pointer-to-data-member.cpp

@@ -303,3 +303,43 @@ int test5(Incomplete *ic, int Incomplete::*member){
 // OGCG: %[[RT_MEMBER:.*]] = getelementptr inbounds i8, ptr %[[IC]], i64 %[[MEMBER]]
 // OGCG: %[[RET:.*]] = load i32, ptr %[[RT_MEMBER]]
 // OGCG: ret i32 %[[RET]]
+
+autotest_null() -> int Point::*{
+returnnullptr;
+}
+
+// CIR: cir.func{{.*}} @_Z9test_nullv() -> !cir.data_member<!s32i in !rec_Point>{
+// CIR: %[[RETVAL_ADDR:.*]] = cir.alloca !cir.data_member<!s32i in !rec_Point>, !cir.ptr<!cir.data_member<!s32i in !rec_Point>>, ["__retval"]
+// CIR: %[[CONST_NULL:.*]] = cir.const #cir.data_member<null> : !cir.data_member<!s32i in !rec_Point>
+// CIR: cir.store %[[CONST_NULL]], %[[RETVAL_ADDR]]
+// CIR: %[[RET:.*]] = cir.load %[[RETVAL_ADDR]]
+// CIR: cir.return %[[RET]] : !cir.data_member<!s32i in !rec_Point>
+
+// LLVM: define{{.*}} i64 @_Z9test_nullv()
+// LLVM: %[[RETVAL_ADDR:.*]] = alloca i64
+// LLVM: store i64 -1, ptr %[[RETVAL_ADDR]]
+// LLVM: %[[RET:.*]] = load i64, ptr %[[RETVAL_ADDR]]
+// LLVM: ret i64 %[[RET]]
+
+// OGCG: define{{.*}} i64 @_Z9test_nullv()
+// OGCG: ret i64 -1
+
+autotest_null_incomplete() -> int Incomplete::*{
+returnnullptr;
+}
+
+// CIR: cir.func{{.*}} @_Z20test_null_incompletev() -> !cir.data_member<!s32i in !rec_Incomplete>{
+// CIR: %[[RETVAL_ADDR:.*]] = cir.alloca !cir.data_member<!s32i in !rec_Incomplete>, !cir.ptr<!cir.data_member<!s32i in !rec_Incomplete>>, ["__retval"]
+// CIR: %[[CONST_NULL:.*]] = cir.const #cir.data_member<null> : !cir.data_member<!s32i in !rec_Incomplete>
+// CIR: cir.store %[[CONST_NULL]], %[[RETVAL_ADDR]]
+// CIR: %[[RET:.*]] = cir.load %[[RETVAL_ADDR]]
+// CIR: cir.return %[[RET]] : !cir.data_member<!s32i in !rec_Incomplete>
+
+// LLVM: define{{.*}} i64 @_Z20test_null_incompletev()
+// LLVM: %[[RETVAL_ADDR:.*]] = alloca i64
+// LLVM: store i64 -1, ptr %[[RETVAL_ADDR]]
+// LLVM: %[[RET:.*]] = load i64, ptr %[[RETVAL_ADDR]]
+// LLVM: ret i64 %[[RET]]
+
+// OGCG: define{{.*}} i64 @_Z20test_null_incompletev()
+// OGCG: ret i64 -1