diff --git a/clang/include/clang/CIR/MissingFeatures.h b/clang/include/clang/CIR/MissingFeatures.h
index 182e4b6784d2f..cc3b0f5b02d35 100644
--- a/clang/include/clang/CIR/MissingFeatures.h
+++ b/clang/include/clang/CIR/MissingFeatures.h
@@ -222,7 +222,6 @@ struct MissingFeatures {
   static bool moduleNameHash() { return false; }
   static bool msabi() { return false; }
   static bool needsGlobalCtorDtor() { return false; }
-  static bool nonFineGrainedBitfields() { return false; }
   static bool objCBlocks() { return false; }
   static bool objCGC() { return false; }
   static bool objCLifetime() { return false; }
diff --git a/clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp b/clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp
index 05e8848884f7e..e4ec380043689 100644
--- a/clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp
@@ -438,9 +438,7 @@ CIRRecordLowering::accumulateBitFields(RecordDecl::field_iterator field,
           } else if (cirGenTypes.getCGModule()
                          .getCodeGenOpts()
                          .FineGrainedBitfieldAccesses) {
-            assert(!cir::MissingFeatures::nonFineGrainedBitfields());
-            cirGenTypes.getCGModule().errorNYI(field->getSourceRange(),
-                                               "NYI FineGrainedBitfield");
+            installBest = true;
           } else {
             // Otherwise, we're not installing. Update the bit size
             // of the current span to go all the way to limitOffset, which is
diff --git a/clang/test/CIR/CodeGen/finegrain-bitfield-access.cpp b/clang/test/CIR/CodeGen/finegrain-bitfield-access.cpp
new file mode 100644
index 0000000000000..930b0a9c70059
--- /dev/null
+++ b/clang/test/CIR/CodeGen/finegrain-bitfield-access.cpp
@@ -0,0 +1,271 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir -ffine-grained-bitfield-accesses %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s --check-prefix=CIR
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm -ffine-grained-bitfield-accesses %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s --check-prefix=LLVM
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -ffine-grained-bitfield-accesses %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s --check-prefix=OGCG
+
+struct S1 {
+  unsigned f1:2;
+  unsigned f2:6;
+  unsigned f3:8;
+  unsigned f4:4;
+  unsigned f5:8;
+};
+
+// CIR-DAG: !rec_S1 = !cir.record<struct "S1" {!u8i, !u8i, !u16i}>
+// LLVM-DAG: %struct.S1 = type { i8, i8, i16 }
+// OGCG-DAG: %struct.S1 = type { i8, i8, i16 }
+
+struct S2 {
+  unsigned long f1:16;
+  unsigned long f2:16;
+  unsigned long f3:6;
+};
+
+// CIR-DAG: !rec_S2 = !cir.record<struct "S2" padded {!u16i, !u16i, !u8i, !cir.array<!u8i x 3>}>
+// LLVM-DAG: %struct.S2 = type { i16, i16, i8, [3 x i8] }
+// OGCG-DAG: %struct.S2 = type { i16, i16, i8, [3 x i8] }
+
+struct S3 {
+  unsigned long f1:14;
+  unsigned long f2:18;
+  unsigned long f3:32;
+};
+
+// CIR-DAG: !rec_S3 = !cir.record<struct "S3" {!u32i, !u32i}>
+// LLVM-DAG: %struct.S3 = type { i32, i32 }
+// OGCG-DAG: %struct.S3 = type { i32, i32 }
+
+S1 a1;
+S2 a2;
+S3 a3;
+
+unsigned read8_1() {
+  return a1.f3;
+}
+
+// CIR-LABEL: @_Z7read8_1v
+// CIR: [[MEMBER:%.*]] = cir.get_member %1[1] {name = "f3"} : !cir.ptr<!rec_S1> -> !cir.ptr<!u8i>
+// CIR: [[BITFI:%.*]] = cir.get_bitfield align(1) (#bfi_f3, [[MEMBER]] : !cir.ptr<!u8i>) -> !u32i
+// CIR: cir.store [[BITFI]], {{.*}} : !u32i, !cir.ptr<!u32i>
+// CIR: [[RET:%.*]] = cir.load {{.*}} : !cir.ptr<!u32i>, !u32i
+// CIR: cir.return [[RET]] : !u32i
+
+// LLVM-LABEL: @_Z7read8_1v
+// LLVM:  [[MEMBER:%.*]] = load i8, ptr getelementptr inbounds nuw (i8, ptr {{.*}}, i64 1), align 1
+// LLVM:  [[BFCAST:%.*]] = zext i8 [[MEMBER]] to i32
+// LLVM:  store i32 [[BFCAST]], ptr {{.*}}, align 4
+// LLVM:  [[RET:%.*]] = load i32, ptr {{.*}}, align 4
+// LLVM:  ret i32 [[RET]]
+
+// OGCG-LABEL: @_Z7read8_1v
+// OGCG: [[BFLOAD:%.*]] = load i8, ptr getelementptr inbounds nuw (%struct.S1, ptr {{.*}}, i32 0, i32 1), align 1
+// OGCG-NEXT: [[BFCAST:%.*]] = zext i8 [[BFLOAD]] to i32
+// OGCG-NEXT: ret i32 [[BFCAST]]
+
+void write8_1() {
+  a1.f3 = 3;
+}
+
+// CIR-LABEL: @_Z8write8_1v
+// CIR: [[CONST3:%.*]] = cir.const #cir.int<3> : !s32i
+// CIR: [[INT3:%.*]] = cir.cast(integral, [[CONST3]] : !s32i), !u32i
+// CIR: [[MEMBER:%.*]] = cir.get_member {{.*}}[1] {name = "f3"} : !cir.ptr<!rec_S1> -> !cir.ptr<!u8i>
+// CIR: cir.set_bitfield align(1) (#bfi_f3, [[MEMBER]] : !cir.ptr<!u8i>, [[INT3]] : !u32i) -> !u32i
+
+// LLVM-LABEL: @_Z8write8_1v
+// LLVM:  store i8 3, ptr getelementptr inbounds nuw (i8, ptr {{.*}}, i64 1), align 1
+// LLVM:  ret void
+
+// OGCG-LABEL: @_Z8write8_1v
+// OGCG: store i8 3, ptr getelementptr inbounds nuw (%struct.S1, ptr {{.*}}, i32 0, i32 1), align 1
+// OGCG-NEXT: ret void
+
+unsigned read8_2() {
+
+  return a1.f5;
+}
+
+// CIR-LABEL: @_Z7read8_2v
+// CIR: [[MEMBER:%.*]] = cir.get_member {{.*}}[2] {name = "f5"} : !cir.ptr<!rec_S1> -> !cir.ptr<!u16i>
+// CIR: [[BITFI:%.*]] = cir.get_bitfield align(2) (#bfi_f5, [[MEMBER]] : !cir.ptr<!u16i>) -> !u32i
+// CIR: cir.store [[BITFI]], {{.*}} : !u32i, !cir.ptr<!u32i>
+// CIR: [[RET:%.*]] = cir.load {{.*}} : !cir.ptr<!u32i>, !u32i
+// CIR: cir.return [[RET]] : !u32i
+
+// LLVM-LABEL: @_Z7read8_2v
+// LLVM:  [[BFLOAD:%.*]] = load i16, ptr getelementptr inbounds nuw (i8, ptr {{.*}}, i64 2), align 2
+// LLVM:  [[BFLSHR:%.*]] = lshr i16 [[BFLOAD]], 4
+// LLVM:  [[BFCLEAR:%.*]] = and i16 [[BFLSHR]], 255
+// LLVM:  [[BFCAST:%.*]] = zext i16 [[BFCLEAR]] to i32
+// LLVM:  store i32 [[BFCAST]], ptr {{.*}}, align 4
+// LLVM:  [[RET:%.*]] = load i32, ptr {{.*}}, align 4
+// LLVM:  ret i32 [[RET]]
+
+// OGCG-LABEL: @_Z7read8_2v
+// OGCG: [[BFLOAD:%.*]] = load i16, ptr getelementptr inbounds nuw (%struct.S1, ptr {{.*}}, i32 0, i32 2), align 2
+// OGCG-NEXT: [[BFLSHR:%.*]] = lshr i16 [[BFLOAD]], 4
+// OGCG-NEXT: [[BFCLEAR:%.*]] = and i16 [[BFLSHR]], 255
+// OGCG-NEXT: [[BFCAST:%.*]] = zext i16 [[BFCLEAR]] to i32
+// OGCG-NEXT: ret i32 [[BFCAST]]
+
+void write8_2() {
+  a1.f5 = 3;
+}
+
+// CIR-LABEL: @_Z8write8_2v
+// CIR: [[CONST3:%.*]] = cir.const #cir.int<3> : !s32i
+// CIR: [[INT3:%.*]] = cir.cast(integral, [[CONST3]] : !s32i), !u32i
+// CIR: [[MEMBER:%.*]] = cir.get_member {{.*}}[2] {name = "f5"} : !cir.ptr<!rec_S1> -> !cir.ptr<!u16i>
+// CIR: cir.set_bitfield align(2) (#bfi_f5, %3 : !cir.ptr<!u16i>, {{.*}} : !u32i) -> !u32i
+
+// LLVM-LABEL: @_Z8write8_2v
+// LLVM:  [[BFLOAD:%.*]] = load i16, ptr getelementptr inbounds nuw (i8, ptr {{.*}}, i64 2), align 2
+// LLVM:  [[BFCLEAR:%.*]] = and i16 [[BFLOAD]], -4081
+// LLVM:  [[BFSET:%.*]] = or i16 [[BFCLEAR]], 48
+// LLVM:  store i16 [[BFSET]], ptr getelementptr inbounds nuw (i8, ptr {{.*}}, i64 2), align 2
+// LLVM:  ret void
+
+// OGCG-LABEL: @_Z8write8_2v
+// OGCG: [[BFLOAD:%.*]] = load i16, ptr getelementptr inbounds nuw (%struct.S1, ptr {{.*}}, i32 0, i32 2), align 2
+// OGCG-NEXT: [[BFCLEAR:%.*]] = and i16 [[BFLOAD]], -4081
+// OGCG-NEXT: [[BFSET:%.*]] = or i16 [[BFCLEAR]], 48
+// OGCG-NEXT: store i16 [[BFSET]], ptr getelementptr inbounds nuw (%struct.S1, ptr {{.*}}, i32 0, i32 2), align 2
+// OGCG-NEXT: ret void
+
+unsigned read16_1() {
+  return a2.f1;
+}
+
+// CIR-LABEL: @_Z8read16_1v
+// CIR: [[MEMBER:%.*]] = cir.get_member {{.*}}[0] {name = "f1"} : !cir.ptr<!rec_S2> -> !cir.ptr<!u16i>
+// CIR: [[BITFI:%.*]] = cir.get_bitfield align(8) (#bfi_f1, [[MEMBER]] : !cir.ptr<!u16i>) -> !u64i
+// CIR: [[BFCAST:%.*]] = cir.cast(integral, [[BITFI]] : !u64i), !u32i
+// CIR: cir.store [[BFCAST]], {{.*}} : !u32i, !cir.ptr<!u32i>
+// CIR: [[RET:%.*]] = cir.load {{.*}} : !cir.ptr<!u32i>, !u32i
+// CIR: cir.return [[RET]] : !u32i
+
+// LLVM-LABEL: @_Z8read16_1v
+// LLVM:  [[BFLOAD:%.*]] = load i16, ptr {{.*}}, align 8
+// LLVM:  [[BFCAST:%.*]] = zext i16 [[BFLOAD]] to i64
+// LLVM:  [[BF:%.*]] = trunc i64 [[BFCAST]] to i32
+// LLVM:  store i32 [[BF]], ptr {{.*}}, align 4
+// LLVM:  [[RET:%.*]] = load i32, ptr {{.*}}, align 4
+// LLVM:  ret i32 [[RET]]
+
+// OGCG-LABEL: @_Z8read16_1v
+// OGCG: [[BFLOAD:%.*]] = load i16, ptr {{.*}}, align 8
+// OGCG-NEXT: [[BFCAST:%.*]] = zext i16 [[BFLOAD]] to i64
+// OGCG-NEXT: [[RET:%.*]] = trunc i64 [[BFCAST]] to i32
+// OGCG-NEXT: ret i32 [[RET]]
+
+unsigned read16_2() {
+  return a2.f2;
+}
+
+// CIR-LABEL: @_Z8read16_2v
+// CIR: [[MEMBER:%.*]] = cir.get_member {{.*}}[1] {name = "f2"} : !cir.ptr<!rec_S2> -> !cir.ptr<!u16i>
+// CIR: [[BITFI:%.*]] = cir.get_bitfield align(2) (#bfi_f2, [[MEMBER]] : !cir.ptr<!u16i>) -> !u64i
+// CIR: [[BFCAST:%.*]] = cir.cast(integral, [[BITFI]] : !u64i), !u32i
+// CIR: cir.store [[BFCAST]], {{.*}} : !u32i, !cir.ptr<!u32i>
+// CIR: [[RET:%.*]] = cir.load {{.*}} : !cir.ptr<!u32i>, !u32i
+// CIR: cir.return [[RET]] : !u32i
+
+// LLVM-LABEL: @_Z8read16_2v
+// LLVM:  [[BFLOAD:%.*]] = load i16, ptr getelementptr inbounds nuw (i8, ptr {{.*}}, i64 2), align 2
+// LLVM:  [[BFCAST:%.*]] = zext i16 [[BFLOAD]] to i64
+// LLVM:  [[BF:%.*]] = trunc i64 [[BFCAST]] to i32
+// LLVM:  store i32 [[BF]], ptr {{.*}}, align 4
+// LLVM:  [[RET:%.*]] = load i32, ptr {{.*}}, align 4
+// LLVM:  ret i32 [[RET]]
+
+// OGCG-LABEL: @_Z8read16_2v
+// OGCG: [[BFLOAD:%.*]] = load i16, ptr getelementptr inbounds nuw (%struct.S2, ptr {{.*}}, i32 0, i32 1), align 2
+// OGCG-NEXT: [[BFCAST:%.*]] = zext i16 [[BFLOAD]] to i64
+// OGCG-NEXT: [[RET:%.*]] = trunc i64 [[BFCAST]] to i32
+// OGCG-NEXT: ret i32 [[RET]]
+
+void write16_1() {
+  a2.f1 = 5;
+}
+
+// CIR-LABEL: @_Z9write16_1v
+// CIR: [[CONST5:%.*]] = cir.const #cir.int<5> : !s32i
+// CIR: [[INT5:%.*]] = cir.cast(integral, [[CONST5]] : !s32i), !u64i
+// CIR: [[MEMBER:%.*]]  = cir.get_member {{.*}}[0] {name = "f1"} : !cir.ptr<!rec_S2> -> !cir.ptr<!u16i>
+// CIR: cir.set_bitfield align(8) (#bfi_f1, [[MEMBER]] : !cir.ptr<!u16i>, [[INT5]] : !u64i) -> !u64i
+// CIR: cir.return
+
+// LLVM-LABEL: @_Z9write16_1v
+// LLVM:  store i16 5, ptr {{.*}}, align 8
+// LLVM:  ret void
+
+// OGCG-LABEL: @_Z9write16_1v
+// OGCG: store i16 5, ptr {{.*}}, align 8
+// OGCG-NEXT: ret void
+
+void write16_2() {
+
+  a2.f2 = 5;
+}
+
+// CIR-LABEL: @_Z9write16_2v
+// CIR: [[CONST5:%.*]] = cir.const #cir.int<5> : !s32i
+// CIR: [[INT5:%.*]] = cir.cast(integral, [[CONST5]] : !s32i), !u64i
+// CIR: [[MEMBER:%.*]] = cir.get_member {{.*}}[1] {name = "f2"} : !cir.ptr<!rec_S2> -> !cir.ptr<!u16i>
+// CIR: cir.set_bitfield align(2) (#bfi_f2, [[MEMBER]] : !cir.ptr<!u16i>, {{.*}} : !u64i) -> !u64i
+// CIR: cir.return
+
+// LLVM-LABEL: @_Z9write16_2v
+// LLVM: store i16 5, ptr getelementptr inbounds nuw (i8, ptr {{.*}}, i64 2), align 2
+// LLVM: ret void
+
+// OGCG-LABEL: @_Z9write16_2v
+// OGCG: store i16 5, ptr getelementptr inbounds nuw (%struct.S2, ptr {{.*}}, i32 0, i32 1), align 2
+// OGCG-NEXT: ret void
+
+unsigned read32_1() {
+
+  return a3.f3;
+}
+// CIR-LABEL: @_Z8read32_1v
+// CIR: [[MEMBER:%.*]] = cir.get_member {{.*}}[1] {name = "f3"} : !cir.ptr<!rec_S3> -> !cir.ptr<!u32i>
+// CIR: [[BITFI:%.*]] = cir.get_bitfield align(4) (#bfi_f3_1, [[MEMBER]] : !cir.ptr<!u32i>) -> !u64i
+// CIR: [[BFCAST:%.*]] = cir.cast(integral, [[BITFI]] : !u64i), !u32i
+// CIR: cir.store [[BFCAST]], {{.*}} : !u32i, !cir.ptr<!u32i>
+// CIR: [[RET:%.*]] = cir.load {{.*}} : !cir.ptr<!u32i>, !u32i
+// CIR: cir.return [[RET]] : !u32i
+
+// LLVM-LABEL: @_Z8read32_1v
+// LLVM: [[BFLOAD:%.*]] = load i32, ptr getelementptr inbounds nuw (i8, ptr {{.*}}, i64 4), align 4
+// LLVM: [[BFCAST:%.*]] = zext i32 [[BFLOAD]] to i64
+// LLVM: [[BF:%.*]] = trunc i64 [[BFCAST]] to i32
+// LLVM: store i32 [[BF]], ptr {{.*}}, align 4
+// LLVM: [[RET:%.*]] = load i32, ptr {{.*}}, align 4
+// LLVM: ret i32 [[RET]]
+
+// OGCG-LABEL: @_Z8read32_1v
+// OGCG: [[BFLOAD:%.*]] = load i32, ptr getelementptr inbounds nuw (%struct.S3, ptr {{.*}}, i32 0, i32 1), align 4
+// OGCG-NEXT: [[BFCAST:%.*]] = zext i32 %bf.load to i64
+// OGCG-NEXT: [[RET:%.*]] = trunc i64 %bf.cast to i32
+// OGCG-NEXT: ret i32 [[RET]]
+
+void write32_1() {
+  a3.f3 = 5;
+}
+
+// CIR-LABEL: @_Z9write32_1v
+// CIR: [[CONST5:%.*]] = cir.const #cir.int<5> : !s32i
+// CIR: [[INT5:%.*]] = cir.cast(integral, [[CONST5]] : !s32i), !u64i
+// CIR: [[MEMBER:%.*]] = cir.get_member {{.*}}[1] {name = "f3"} : !cir.ptr<!rec_S3> -> !cir.ptr<!u32i>
+// CIR: cir.set_bitfield align(4) (#bfi_f3_1, [[MEMBER]] : !cir.ptr<!u32i>, [[INT5]] : !u64i) -> !u64i
+// CIR: cir.return
+
+// LLVM-LABEL: @_Z9write32_1v
+// LLVM:  store i32 5, ptr getelementptr inbounds nuw (i8, ptr {{.*}}, i64 4), align 4
+// LLVM:  ret void
+
+// OGCG-LABEL: @_Z9write32_1v
+// OGCG: store i32 5, ptr getelementptr inbounds nuw (%struct.S3, ptr {{.*}}, i32 0, i32 1), align 4
+// OGCG-NEXT: ret void