[CIR] Fix access to bitfields inside a union

Author: Andres-Salamanca

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

@@ -372,9 +372,11 @@ Address CIRGenFunction::getAddrOfBitFieldStorage(LValue base,
                                                  unsigned index) {
   mlir::Location loc = getLoc(field->getLocation());
   cir::PointerType fieldPtr = cir::PointerType::get(fieldType);
+  auto rec = cast<cir::RecordType>(base.getAddress().getElementType());
+  if (index == 0 && rec.isUnion())
+    return base.getAddress();
   cir::GetMemberOp sea = getBuilder().createGetMember(
       loc, fieldPtr, base.getPointer(), field->getName(), index);
-  auto rec = cast<cir::RecordType>(base.getAddress().getElementType());
   CharUnits offset = CharUnits::fromQuantity(
       rec.getElementOffset(cgm.getDataLayout().layout, index));
   return Address(sea, base.getAlignment().alignmentAtOffset(offset));

clang/test/CIR/CodeGen/bitfield-union.c

@@ -28,3 +28,44 @@ typedef union {
 
 demo d;
 zero_bit z;
+
+int main() {
+    demo d;
+    d.x = 1;
+    d.y = 2;
+    d.z = 0;
+}
+
+// CIR: #bfi_y = #cir.bitfield_info<name = "y", storage_type = !u8i, size = 4, offset = 0, is_signed = true>
+// CIR: #bfi_z = #cir.bitfield_info<name = "z", storage_type = !u8i, size = 8, offset = 0, is_signed = true>
+
+// CIR:   cir.func no_proto dso_local @main
+// CIR:    [[ALLOC:%.*]] = cir.alloca !rec_demo, !cir.ptr<!rec_demo>, ["d"] {alignment = 4 : i64}
+// CIR:    [[ONE:%.*]] = cir.const #cir.int<1> : !s32i
+// CIR:    [[X:%.*]] = cir.get_member [[ALLOC]][0] {name = "x"} : !cir.ptr<!rec_demo> -> !cir.ptr<!s32i>
+// CIR:    cir.store align(4) [[ONE]], [[X]] : !s32i, !cir.ptr<!s32i>
+// CIR:    [[TWO:%.*]] = cir.const #cir.int<2> : !s32i
+// CIR:    [[BITCAST:%.*]] = cir.cast(bitcast, [[ALLOC]] : !cir.ptr<!rec_demo>), !cir.ptr<!u8i>
+// CIR:    [[SET:%.*]] = cir.set_bitfield align(4) (#bfi_y, [[BITCAST]] : !cir.ptr<!u8i>, [[TWO]] : !s32i) -> !s32i
+// CIR:    [[ZERO:%.*]] = cir.const #cir.int<0> : !s32i
+// CIR:    [[BITCAST2:%.*]] = cir.cast(bitcast, [[ALLOC]] : !cir.ptr<!rec_demo>), !cir.ptr<!u8i>
+// CIR:    [[SET2:%.*]] = cir.set_bitfield align(4) (#bfi_z, [[BITCAST2]] : !cir.ptr<!u8i>, [[ZERO]] : !s32i) -> !s32i
+// CIR:    cir.return
+
+// LLVM: define dso_local i32 @main
+// LLVM:   [[ALLOC:%.*]] = alloca %union.demo, i64 1, align 4
+// LLVM:   store i32 1, ptr [[ALLOC]], align 4
+// LLVM:   [[BFLOAD:%.*]] = load i8, ptr [[ALLOC]], align 4
+// LLVM:   [[CLEAR:%.*]] = and i8 [[BFLOAD]], -16
+// LLVM:   [[SET:%.*]] = or i8 [[CLEAR]], 2
+// LLVM:   store i8 [[SET]], ptr [[ALLOC]], align 4
+// LLVM:   store i8 0, ptr [[ALLOC]], align 4
+
+// OGCG: define dso_local i32 @main
+// OGCG:   [[ALLOC:%.*]] = alloca %union.demo, align 4
+// OGCG:   store i32 1, ptr [[ALLOC]], align 4
+// OGCG:   [[BFLOAD:%.*]] = load i8, ptr [[ALLOC]], align 4
+// OGCG:   [[CLEAR:%.*]] = and i8 [[BFLOAD]], -16
+// OGCG:   [[SET:%.*]] = or i8 [[CLEAR]], 2
+// OGCG:   store i8 [[SET]], ptr [[ALLOC]], align 4
+// OGCG:   store i8 0, ptr [[ALLOC]], align 4