[CIR][CIRGen] Achieve union's bitfields additionally. (llvm#742)

Achieve union's bitfields additionally.

Author: 566hub

clang/lib/CIR/CodeGen/CIRRecordLayoutBuilder.cpp

@@ -271,12 +271,6 @@ void CIRRecordLowering::lower(bool nonVirtualBaseType) {
 
   CharUnits Size = nonVirtualBaseType ? astRecordLayout.getNonVirtualSize()
                                       : astRecordLayout.getSize();
-  if (recordDecl->isUnion()) {
-    llvm_unreachable("NYI");
-    // lowerUnion();
-    // computeVolatileBitfields();
-    return;
-  }
   accumulateFields();
 
   // RD implies C++
@@ -316,13 +310,20 @@ void CIRRecordLowering::lowerUnion() {
   // type would work fine and be simpler but would be different than what we've
   // been doing and cause lit tests to change.
   for (const auto *Field : recordDecl->fields()) {
+
+    mlir::Type FieldType = nullptr;
     if (Field->isBitField()) {
       if (Field->isZeroLengthBitField(astContext))
         continue;
-      llvm_unreachable("NYI");
+
+      FieldType = getBitfieldStorageType(Field->getBitWidthValue(astContext));
+
+      setBitFieldInfo(Field, CharUnits::Zero(), FieldType);
+    } else {
+      FieldType = getStorageType(Field);
     }
     fields[Field->getCanonicalDecl()] = 0;
-    auto FieldType = getStorageType(Field);
+    // auto FieldType = getStorageType(Field);
     // Compute zero-initializable status.
     // This union might not be zero initialized: it may contain a pointer to
     // data member which might have some exotic initialization sequence.

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

@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s
+
+void main() {
+    union demo {
+        int x;
+        int y : 4;
+        int z : 8;
+    };
+    union demo d;
+    d.x = 1;
+    d.y = 2;
+    d.z = 0;
+}
+
+// CHECK: !ty_22demo22 = !cir.struct<union "demo" {!s32i, !u8i, !u8i}>
+// CHECK: #bfi_y = #cir.bitfield_info<name = "y", storage_type = !u8i, size = 4, offset = 0, is_signed = true>
+// CHECK: #bfi_z = #cir.bitfield_info<name = "z", storage_type = !u8i, size = 8, offset = 0, is_signed = true>
+
+//   cir.func no_proto @main() extra(#fn_attr) {
+//     %0 = cir.alloca !ty_22demo22, !cir.ptr<!ty_22demo22>, ["d"] {alignment = 4 : i64}
+//     %1 = cir.const #cir.int<1> : !s32i
+//     %2 = cir.get_member %0[0] {name = "x"} : !cir.ptr<!ty_22demo22> -> !cir.ptr<!s32i>
+//     cir.store %1, %2 : !s32i, !cir.ptr<!s32i>
+//     %3 = cir.const #cir.int<2> : !s32i
+//     %4 = cir.cast(bitcast, %0 : !cir.ptr<!ty_22demo22>), !cir.ptr<!u8i>
+//     %5 = cir.set_bitfield(#bfi_y, %4 : !cir.ptr<!u8i>, %3 : !s32i) -> !s32i
+//     %6 = cir.const #cir.int<0> : !s32i loc(#loc10)
+//     %7 = cir.cast(bitcast, %0 : !cir.ptr<!ty_22demo22>), !cir.ptr<!u8i>
+//     %8 = cir.set_bitfield(#bfi_z, %7 : !cir.ptr<!u8i>, %6 : !s32i) -> !s32i
+//     cir.return
+//   }