Merge branch 'raulgrell-BitByteOffsetOfs'

8 files changed, 233 insertions, 72 deletions

diff --git a/doc/langref.html.in b/doc/langref.html.in
index 9bd11b8236..f28c8d6cfa 100644
--- a/doc/langref.html.in
+++ b/doc/langref.html.in
@@ -1947,6 +1947,15 @@ test "linked list" {
     assert(list2.first.?.data == 1234);
 }
       {#code_end#}
+      {#header_open|packed struct#}
+      <p>{#syntax#}packed{#endsyntax#} structs have guaranteed in-memory layout.</p>
+      <p>TODO bit fields</p>
+      <p>TODO alignment</p>
+      <p>TODO endianness</p>
+      <p>TODO @bitOffsetOf and @byteOffsetOf</p>
+      <p>TODO mention how volatile loads and stores of bit packed fields could be more efficient when
+      done by hand instead of with packed struct</p>
+      {#header_close#}
       {#header_open|struct Naming#}
       <p>Since all structs are anonymous, Zig infers the type name based on a few rules.</p>
       <ul>
@@ -5135,6 +5144,18 @@ fn seq(c: u8) void {
       Works at compile-time if {#syntax#}value{#endsyntax#} is known at compile time. It's a compile error to bitcast a struct to a scalar type of the same size since structs have undefined layout. However if the struct is packed then it works.
       </p>
       {#header_close#}
+      {#header_open|@bitOffsetOf#}
+      <pre>{#syntax#}@bitOffsetOf(comptime T: type, comptime field_name: [] const u8) comptime_int{#endsyntax#}</pre>
+      <p>
+      Returns the bit offset of a field relative to its containing struct.
+      </p>
+      <p>
+      For non {#link|packed structs|packed struct#}, this will always be divisible by {#syntax#}8{#endsyntax#}.
+      For packed structs, non-byte-aligned fields will share a byte offset, but they will have different
+      bit offsets.
+      </p>
+      {#see_also|@byteOffsetOf#}
+      {#header_close#}
       {#header_open|@breakpoint#}
       <pre>{#syntax#}@breakpoint(){#endsyntax#}</pre>
       <p>
@@ -5146,6 +5167,13 @@ fn seq(c: u8) void {
       </p>
 
       {#header_close#}
+      {#header_open|@byteOffsetOf#}
+      <pre>{#syntax#}@byteOffsetOf(comptime T: type, comptime field_name: [] const u8) comptime_int{#endsyntax#}</pre>
+      <p>
+      Returns the byte offset of a field relative to its containing struct.
+      </p>
+      {#see_also|@bitOffsetOf#}
+      {#header_close#}
       {#header_open|@alignCast#}
       <pre>{#syntax#}@alignCast(comptime alignment: u29, ptr: var) var{#endsyntax#}</pre>
       <p>
@@ -5868,12 +5896,6 @@ fn add(a: i32, b: i32) i32 {
       </p>
       {#see_also|@inlineCall#}
       {#header_close#}
-      {#header_open|@offsetOf#}
-      <pre>{#syntax#}@offsetOf(comptime T: type, comptime field_name: [] const u8) comptime_int{#endsyntax#}</pre>
-      <p>
-      This function returns the byte offset of a field relative to its containing struct.
-      </p>
-      {#header_close#}
       {#header_open|@OpaqueType#}
       <pre>{#syntax#}@OpaqueType() type{#endsyntax#}</pre>
       <p>
diff --git a/src/all_types.hpp b/src/all_types.hpp
index 290e4bb0dd..0eaf69ed64 100644
--- a/src/all_types.hpp
+++ b/src/all_types.hpp
@@ -1409,7 +1409,8 @@ enum BuiltinFnId {
     BuiltinFnIdTagName,
     BuiltinFnIdTagType,
     BuiltinFnIdFieldParentPtr,
-    BuiltinFnIdOffsetOf,
+    BuiltinFnIdByteOffsetOf,
+    BuiltinFnIdBitOffsetOf,
     BuiltinFnIdInlineCall,
     BuiltinFnIdNoInlineCall,
     BuiltinFnIdNewStackCall,
@@ -2134,7 +2135,8 @@ enum IrInstructionId {
     IrInstructionIdTagName,
     IrInstructionIdTagType,
     IrInstructionIdFieldParentPtr,
-    IrInstructionIdOffsetOf,
+    IrInstructionIdByteOffsetOf,
+    IrInstructionIdBitOffsetOf,
     IrInstructionIdTypeInfo,
     IrInstructionIdTypeId,
     IrInstructionIdSetEvalBranchQuota,
@@ -3037,7 +3039,14 @@ struct IrInstructionFieldParentPtr {
     TypeStructField *field;
 };
 
-struct IrInstructionOffsetOf {
+struct IrInstructionByteOffsetOf {
+    IrInstruction base;
+
+    IrInstruction *type_value;
+    IrInstruction *field_name;
+};
+
+struct IrInstructionBitOffsetOf {
     IrInstruction base;
 
     IrInstruction *type_value;
diff --git a/src/codegen.cpp b/src/codegen.cpp
index 6c4b54261c..d4d57d541c 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -5098,7 +5098,8 @@ static LLVMValueRef ir_render_instruction(CodeGen *g, IrExecutable *executable,
         case IrInstructionIdTypeName:
         case IrInstructionIdDeclRef:
         case IrInstructionIdSwitchVar:
-        case IrInstructionIdOffsetOf:
+        case IrInstructionIdByteOffsetOf:
+        case IrInstructionIdBitOffsetOf:
         case IrInstructionIdTypeInfo:
         case IrInstructionIdTypeId:
         case IrInstructionIdSetEvalBranchQuota:
@@ -6671,7 +6672,8 @@ static void define_builtin_fns(CodeGen *g) {
     create_builtin_fn(g, BuiltinFnIdTagName, "tagName", 1);
     create_builtin_fn(g, BuiltinFnIdTagType, "TagType", 1);
     create_builtin_fn(g, BuiltinFnIdFieldParentPtr, "fieldParentPtr", 3);
-    create_builtin_fn(g, BuiltinFnIdOffsetOf, "offsetOf", 2);
+    create_builtin_fn(g, BuiltinFnIdByteOffsetOf, "byteOffsetOf", 2);
+    create_builtin_fn(g, BuiltinFnIdBitOffsetOf, "bitOffsetOf", 2);
     create_builtin_fn(g, BuiltinFnIdDivExact, "divExact", 2);
     create_builtin_fn(g, BuiltinFnIdDivTrunc, "divTrunc", 2);
     create_builtin_fn(g, BuiltinFnIdDivFloor, "divFloor", 2);
diff --git a/src/ir.cpp b/src/ir.cpp
index 327c4f9398..5e0f79ec13 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -720,8 +720,12 @@ static constexpr IrInstructionId ir_instruction_id(IrInstructionFieldParentPtr *
     return IrInstructionIdFieldParentPtr;
 }
 
-static constexpr IrInstructionId ir_instruction_id(IrInstructionOffsetOf *) {
-    return IrInstructionIdOffsetOf;
+static constexpr IrInstructionId ir_instruction_id(IrInstructionByteOffsetOf *) {
+    return IrInstructionIdByteOffsetOf;
+}
+
+static constexpr IrInstructionId ir_instruction_id(IrInstructionBitOffsetOf *) {
+    return IrInstructionIdBitOffsetOf;
 }
 
 static constexpr IrInstructionId ir_instruction_id(IrInstructionTypeInfo *) {
@@ -2628,10 +2632,23 @@ static IrInstruction *ir_build_field_parent_ptr(IrBuilder *irb, Scope *scope, As
     return &instruction->base;
 }
 
-static IrInstruction *ir_build_offset_of(IrBuilder *irb, Scope *scope, AstNode *source_node,
+static IrInstruction *ir_build_byte_offset_of(IrBuilder *irb, Scope *scope, AstNode *source_node,
         IrInstruction *type_value, IrInstruction *field_name)
 {
-    IrInstructionOffsetOf *instruction = ir_build_instruction<IrInstructionOffsetOf>(irb, scope, source_node);
+    IrInstructionByteOffsetOf *instruction = ir_build_instruction<IrInstructionByteOffsetOf>(irb, scope, source_node);
+    instruction->type_value = type_value;
+    instruction->field_name = field_name;
+
+    ir_ref_instruction(type_value, irb->current_basic_block);
+    ir_ref_instruction(field_name, irb->current_basic_block);
+
+    return &instruction->base;
+}
+
+static IrInstruction *ir_build_bit_offset_of(IrBuilder *irb, Scope *scope, AstNode *source_node,
+        IrInstruction *type_value, IrInstruction *field_name)
+{
+    IrInstructionBitOffsetOf *instruction = ir_build_instruction<IrInstructionBitOffsetOf>(irb, scope, source_node);
     instruction->type_value = type_value;
     instruction->field_name = field_name;
 
@@ -4688,7 +4705,7 @@ static IrInstruction *ir_gen_builtin_fn_call(IrBuilder *irb, Scope *scope, AstNo
                 IrInstruction *field_parent_ptr = ir_build_field_parent_ptr(irb, scope, node, arg0_value, arg1_value, arg2_value, nullptr);
                 return ir_lval_wrap(irb, scope, field_parent_ptr, lval);
             }
-        case BuiltinFnIdOffsetOf:
+        case BuiltinFnIdByteOffsetOf:
             {
                 AstNode *arg0_node = node->data.fn_call_expr.params.at(0);
                 IrInstruction *arg0_value = ir_gen_node(irb, arg0_node, scope);
@@ -4700,7 +4717,22 @@ static IrInstruction *ir_gen_builtin_fn_call(IrBuilder *irb, Scope *scope, AstNo
                 if (arg1_value == irb->codegen->invalid_instruction)
                     return arg1_value;
 
-                IrInstruction *offset_of = ir_build_offset_of(irb, scope, node, arg0_value, arg1_value);
+                IrInstruction *offset_of = ir_build_byte_offset_of(irb, scope, node, arg0_value, arg1_value);
+                return ir_lval_wrap(irb, scope, offset_of, lval);
+            }
+        case BuiltinFnIdBitOffsetOf:
+            {
+                AstNode *arg0_node = node->data.fn_call_expr.params.at(0);
+                IrInstruction *arg0_value = ir_gen_node(irb, arg0_node, scope);
+                if (arg0_value == irb->codegen->invalid_instruction)
+                    return arg0_value;
+
+                AstNode *arg1_node = node->data.fn_call_expr.params.at(1);
+                IrInstruction *arg1_value = ir_gen_node(irb, arg1_node, scope);
+                if (arg1_value == irb->codegen->invalid_instruction)
+                    return arg1_value;
+
+                IrInstruction *offset_of = ir_build_bit_offset_of(irb, scope, node, arg0_value, arg1_value);
                 return ir_lval_wrap(irb, scope, offset_of, lval);
             }
         case BuiltinFnIdInlineCall:
@@ -17010,49 +17042,84 @@ static ZigType *ir_analyze_instruction_field_parent_ptr(IrAnalyze *ira,
     return result_type;
 }
 
-static ZigType *ir_analyze_instruction_offset_of(IrAnalyze *ira,
-        IrInstructionOffsetOf *instruction)
+static TypeStructField *validate_byte_offset(IrAnalyze *ira,
+        IrInstruction *type_value,
+        IrInstruction *field_name_value,
+        size_t *byte_offset) 
 {
-    Error err;
-    IrInstruction *type_value = instruction->type_value->other;
     ZigType *container_type = ir_resolve_type(ira, type_value);
     if (type_is_invalid(container_type))
-        return ira->codegen->builtin_types.entry_invalid;
+        return nullptr;
 
+    Error err;
     if ((err = ensure_complete_type(ira->codegen, container_type)))
-        return ira->codegen->builtin_types.entry_invalid;
+        return nullptr;
 
-    IrInstruction *field_name_value = instruction->field_name->other;
     Buf *field_name = ir_resolve_str(ira, field_name_value);
     if (!field_name)
-        return ira->codegen->builtin_types.entry_invalid;
+        return nullptr;
 
     if (container_type->id != ZigTypeIdStruct) {
         ir_add_error(ira, type_value,
                 buf_sprintf("expected struct type, found '%s'", buf_ptr(&container_type->name)));
-        return ira->codegen->builtin_types.entry_invalid;
+        return nullptr;
     }
 
     TypeStructField *field = find_struct_type_field(container_type, field_name);
     if (field == nullptr) {
         ir_add_error(ira, field_name_value,
                 buf_sprintf("struct '%s' has no field '%s'",
-                    buf_ptr(&container_type->name), buf_ptr(field_name)));
-        return ira->codegen->builtin_types.entry_invalid;
+                        buf_ptr(&container_type->name), buf_ptr(field_name)));
+        return nullptr;
     }
 
     if (!type_has_bits(field->type_entry)) {
         ir_add_error(ira, field_name_value,
-                     buf_sprintf("zero-bit field '%s' in struct '%s' has no offset",
-                                 buf_ptr(field_name), buf_ptr(&container_type->name)));
-        return ira->codegen->builtin_types.entry_invalid;
+                buf_sprintf("zero-bit field '%s' in struct '%s' has no offset",
+                        buf_ptr(field_name), buf_ptr(&container_type->name)));
+        return nullptr;
     }
-    size_t byte_offset = LLVMOffsetOfElement(ira->codegen->target_data_ref, container_type->type_ref, field->gen_index);
+
+    *byte_offset = LLVMOffsetOfElement(ira->codegen->target_data_ref, container_type->type_ref, field->gen_index);
+    return field;
+}
+
+static ZigType *ir_analyze_instruction_byte_offset_of(IrAnalyze *ira,
+        IrInstructionByteOffsetOf *instruction)
+{
+    IrInstruction *type_value = instruction->type_value->other;
+    if (type_is_invalid(type_value->value.type))
+        return ira->codegen->builtin_types.entry_invalid;
+
+    IrInstruction *field_name_value = instruction->field_name->other;
+    size_t byte_offset = 0;
+    if (!validate_byte_offset(ira, type_value, field_name_value, &byte_offset))
+        return ira->codegen->builtin_types.entry_invalid;
+
+
     ConstExprValue *out_val = ir_build_const_from(ira, &instruction->base);
     bigint_init_unsigned(&out_val->data.x_bigint, byte_offset);
     return ira->codegen->builtin_types.entry_num_lit_int;
 }
 
+static ZigType *ir_analyze_instruction_bit_offset_of(IrAnalyze *ira,
+        IrInstructionBitOffsetOf *instruction)
+{
+    IrInstruction *type_value = instruction->type_value->other;
+    if (type_is_invalid(type_value->value.type))
+        return ira->codegen->builtin_types.entry_invalid;
+    IrInstruction *field_name_value = instruction->field_name->other;
+    size_t byte_offset = 0;
+    TypeStructField *field = nullptr;
+    if (!(field = validate_byte_offset(ira, type_value, field_name_value, &byte_offset)))
+        return ira->codegen->builtin_types.entry_invalid;
+
+    size_t bit_offset = byte_offset * 8 + field->packed_bits_offset;
+    ConstExprValue *out_val = ir_build_const_from(ira, &instruction->base);
+    bigint_init_unsigned(&out_val->data.x_bigint, bit_offset);
+    return ira->codegen->builtin_types.entry_num_lit_int;
+}
+
 static void ensure_field_index(ZigType *type, const char *field_name, size_t index)
 {
     Buf *field_name_buf;
@@ -21550,8 +21617,10 @@ static ZigType *ir_analyze_instruction_nocast(IrAnalyze *ira, IrInstruction *ins
             return ir_analyze_instruction_enum_tag_name(ira, (IrInstructionTagName *)instruction);
         case IrInstructionIdFieldParentPtr:
             return ir_analyze_instruction_field_parent_ptr(ira, (IrInstructionFieldParentPtr *)instruction);
-        case IrInstructionIdOffsetOf:
-            return ir_analyze_instruction_offset_of(ira, (IrInstructionOffsetOf *)instruction);
+        case IrInstructionIdByteOffsetOf:
+            return ir_analyze_instruction_byte_offset_of(ira, (IrInstructionByteOffsetOf *)instruction);
+        case IrInstructionIdBitOffsetOf:
+            return ir_analyze_instruction_bit_offset_of(ira, (IrInstructionBitOffsetOf *)instruction);
         case IrInstructionIdTypeInfo:
             return ir_analyze_instruction_type_info(ira, (IrInstructionTypeInfo *) instruction);
         case IrInstructionIdTypeId:
@@ -21835,7 +21904,8 @@ bool ir_has_side_effects(IrInstruction *instruction) {
         case IrInstructionIdTypeName:
         case IrInstructionIdTagName:
         case IrInstructionIdFieldParentPtr:
-        case IrInstructionIdOffsetOf:
+        case IrInstructionIdByteOffsetOf:
+        case IrInstructionIdBitOffsetOf:
         case IrInstructionIdTypeInfo:
         case IrInstructionIdTypeId:
         case IrInstructionIdAlignCast:
diff --git a/src/ir_print.cpp b/src/ir_print.cpp
index d57d554c72..dc756cf492 100644
--- a/src/ir_print.cpp
+++ b/src/ir_print.cpp
@@ -1041,8 +1041,16 @@ static void ir_print_field_parent_ptr(IrPrint *irp, IrInstructionFieldParentPtr
     fprintf(irp->f, ")");
 }
 
-static void ir_print_offset_of(IrPrint *irp, IrInstructionOffsetOf *instruction) {
-    fprintf(irp->f, "@offset_of(");
+static void ir_print_byte_offset_of(IrPrint *irp, IrInstructionByteOffsetOf *instruction) {
+    fprintf(irp->f, "@byte_offset_of(");
+    ir_print_other_instruction(irp, instruction->type_value);
+    fprintf(irp->f, ",");
+    ir_print_other_instruction(irp, instruction->field_name);
+    fprintf(irp->f, ")");
+}
+
+static void ir_print_bit_offset_of(IrPrint *irp, IrInstructionBitOffsetOf *instruction) {
+    fprintf(irp->f, "@bit_offset_of(");
     ir_print_other_instruction(irp, instruction->type_value);
     fprintf(irp->f, ",");
     ir_print_other_instruction(irp, instruction->field_name);
@@ -1649,8 +1657,11 @@ static void ir_print_instruction(IrPrint *irp, IrInstruction *instruction) {
         case IrInstructionIdFieldParentPtr:
             ir_print_field_parent_ptr(irp, (IrInstructionFieldParentPtr *)instruction);
             break;
-        case IrInstructionIdOffsetOf:
-            ir_print_offset_of(irp, (IrInstructionOffsetOf *)instruction);
+        case IrInstructionIdByteOffsetOf:
+            ir_print_byte_offset_of(irp, (IrInstructionByteOffsetOf *)instruction);
+            break;
+        case IrInstructionIdBitOffsetOf:
+            ir_print_bit_offset_of(irp, (IrInstructionBitOffsetOf *)instruction);
             break;
         case IrInstructionIdTypeInfo:
             ir_print_type_info(irp, (IrInstructionTypeInfo *)instruction);
diff --git a/std/c/darwin.zig b/std/c/darwin.zig
index 2e238e40eb..86c5e4828e 100644
--- a/std/c/darwin.zig
+++ b/std/c/darwin.zig
@@ -158,12 +158,12 @@ const std = @import("../index.zig");
 const assert = std.debug.assert;
 
 comptime {
-    assert(@offsetOf(Kevent, "ident") == 0);
-    assert(@offsetOf(Kevent, "filter") == 8);
-    assert(@offsetOf(Kevent, "flags") == 10);
-    assert(@offsetOf(Kevent, "fflags") == 12);
-    assert(@offsetOf(Kevent, "data") == 16);
-    assert(@offsetOf(Kevent, "udata") == 24);
+    assert(@byteOffsetOf(Kevent, "ident") == 0);
+    assert(@byteOffsetOf(Kevent, "filter") == 8);
+    assert(@byteOffsetOf(Kevent, "flags") == 10);
+    assert(@byteOffsetOf(Kevent, "fflags") == 12);
+    assert(@byteOffsetOf(Kevent, "data") == 16);
+    assert(@byteOffsetOf(Kevent, "udata") == 24);
 }
 
 pub const kevent64_s = extern struct {
@@ -180,11 +180,11 @@ pub const kevent64_s = extern struct {
 // to make sure the struct is laid out the same. These values were
 // produced from C code using the offsetof macro.
 comptime {
-    assert(@offsetOf(kevent64_s, "ident") == 0);
-    assert(@offsetOf(kevent64_s, "filter") == 8);
-    assert(@offsetOf(kevent64_s, "flags") == 10);
-    assert(@offsetOf(kevent64_s, "fflags") == 12);
-    assert(@offsetOf(kevent64_s, "data") == 16);
-    assert(@offsetOf(kevent64_s, "udata") == 24);
-    assert(@offsetOf(kevent64_s, "ext") == 32);
+    assert(@byteOffsetOf(kevent64_s, "ident") == 0);
+    assert(@byteOffsetOf(kevent64_s, "filter") == 8);
+    assert(@byteOffsetOf(kevent64_s, "flags") == 10);
+    assert(@byteOffsetOf(kevent64_s, "fflags") == 12);
+    assert(@byteOffsetOf(kevent64_s, "data") == 16);
+    assert(@byteOffsetOf(kevent64_s, "udata") == 24);
+    assert(@byteOffsetOf(kevent64_s, "ext") == 32);
 }
diff --git a/test/cases/sizeof_and_typeof.zig b/test/cases/sizeof_and_typeof.zig
index ee2061c8cb..11c6b2f6ba 100644
--- a/test/cases/sizeof_and_typeof.zig
+++ b/test/cases/sizeof_and_typeof.zig
@@ -1,6 +1,7 @@
+const builtin = @import("builtin");
 const assert = @import("std").debug.assert;
 
-test "sizeofAndTypeOf" {
+test "@sizeOf and @typeOf" {
     const y: @typeOf(x) = 120;
     assert(@sizeOf(@typeOf(y)) == 2);
 }
@@ -11,24 +12,58 @@ const A = struct {
     a: u8,
     b: u32,
     c: u8,
+    d: u3,
+    e: u5,
+    f: u16,
+    g: u16,
 };
 
 const P = packed struct {
     a: u8,
     b: u32,
     c: u8,
+    d: u3,
+    e: u5,
+    f: u16,
+    g: u16,
 };
 
-test "offsetOf" {
+test "@byteOffsetOf" {
     // Packed structs have fixed memory layout
-    const p: P = undefined;
-    assert(@offsetOf(P, "a") == 0);
-    assert(@offsetOf(@typeOf(p), "b") == 1);
-    assert(@offsetOf(@typeOf(p), "c") == 5);
+    assert(@byteOffsetOf(P, "a") == 0);
+    assert(@byteOffsetOf(P, "b") == 1);
+    assert(@byteOffsetOf(P, "c") == 5);
+    assert(@byteOffsetOf(P, "d") == 6);
+    assert(@byteOffsetOf(P, "e") == 6);
+    assert(@byteOffsetOf(P, "f") == 7);
+    assert(@byteOffsetOf(P, "g") == 9);
 
-    // Non-packed struct fields can be moved/padded
-    const a: A = undefined;
-    assert(@ptrToInt(&a.a) - @ptrToInt(&a) == @offsetOf(A, "a"));
-    assert(@ptrToInt(&a.b) - @ptrToInt(&a) == @offsetOf(@typeOf(a), "b"));
-    assert(@ptrToInt(&a.c) - @ptrToInt(&a) == @offsetOf(@typeOf(a), "c"));
+    // Normal struct fields can be moved/padded
+    var a: A = undefined;
+    assert(@ptrToInt(&a.a) - @ptrToInt(&a) == @byteOffsetOf(A, "a"));
+    assert(@ptrToInt(&a.b) - @ptrToInt(&a) == @byteOffsetOf(A, "b"));
+    assert(@ptrToInt(&a.c) - @ptrToInt(&a) == @byteOffsetOf(A, "c"));
+    assert(@ptrToInt(&a.d) - @ptrToInt(&a) == @byteOffsetOf(A, "d"));
+    assert(@ptrToInt(&a.e) - @ptrToInt(&a) == @byteOffsetOf(A, "e"));
+    assert(@ptrToInt(&a.f) - @ptrToInt(&a) == @byteOffsetOf(A, "f"));
+    assert(@ptrToInt(&a.g) - @ptrToInt(&a) == @byteOffsetOf(A, "g"));
+}
+
+test "@bitOffsetOf" {
+    // Packed structs have fixed memory layout
+    assert(@bitOffsetOf(P, "a") == 0);
+    assert(@bitOffsetOf(P, "b") == 8);
+    assert(@bitOffsetOf(P, "c") == 40);
+    assert(@bitOffsetOf(P, "d") == 48);
+    assert(@bitOffsetOf(P, "e") == 51);
+    assert(@bitOffsetOf(P, "f") == 56);
+    assert(@bitOffsetOf(P, "g") == 72);
+
+    assert(@byteOffsetOf(A, "a") * 8 == @bitOffsetOf(A, "a"));
+    assert(@byteOffsetOf(A, "b") * 8 == @bitOffsetOf(A, "b"));
+    assert(@byteOffsetOf(A, "c") * 8 == @bitOffsetOf(A, "c"));
+    assert(@byteOffsetOf(A, "d") * 8 == @bitOffsetOf(A, "d"));
+    assert(@byteOffsetOf(A, "e") * 8 == @bitOffsetOf(A, "e"));
+    assert(@byteOffsetOf(A, "f") * 8 == @bitOffsetOf(A, "f"));
+    assert(@byteOffsetOf(A, "g") * 8 == @bitOffsetOf(A, "g"));
 }
diff --git a/test/compile_errors.zig b/test/compile_errors.zig
index dfe17e9d82..fae022f3fb 100644
--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -3763,25 +3763,25 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
     );
 
     cases.add(
-        "@offsetOf - non struct",
+        "@byteOffsetOf - non struct",
         \\const Foo = i32;
         \\export fn foo() usize {
-        \\    return @offsetOf(Foo, "a",);
+        \\    return @byteOffsetOf(Foo, "a",);
         \\}
     ,
-        ".tmp_source.zig:3:22: error: expected struct type, found 'i32'",
+        ".tmp_source.zig:3:26: error: expected struct type, found 'i32'",
     );
 
     cases.add(
-        "@offsetOf - bad field name",
+        "@byteOffsetOf - bad field name",
         \\const Foo = struct {
         \\    derp: i32,
         \\};
         \\export fn foo() usize {
-        \\    return @offsetOf(Foo, "a",);
+        \\    return @byteOffsetOf(Foo, "a",);
         \\}
     ,
-        ".tmp_source.zig:5:27: error: struct 'Foo' has no field 'a'",
+        ".tmp_source.zig:5:31: error: struct 'Foo' has no field 'a'",
     );
 
     cases.addExe(
@@ -5084,15 +5084,27 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
     );
 
     cases.add(
-        "taking offset of void field in struct",
+        "taking byte offset of void field in struct",
         \\const Empty = struct {
         \\    val: void,
         \\};
         \\export fn foo() void {
-        \\    const fieldOffset = @offsetOf(Empty, "val",);
+        \\    const fieldOffset = @byteOffsetOf(Empty, "val",);
         \\}
     ,
-        ".tmp_source.zig:5:42: error: zero-bit field 'val' in struct 'Empty' has no offset",
+        ".tmp_source.zig:5:46: error: zero-bit field 'val' in struct 'Empty' has no offset",
+    );
+
+    cases.add(
+        "taking bit offset of void field in struct",
+        \\const Empty = struct {
+        \\    val: void,
+        \\};
+        \\export fn foo() void {
+        \\    const fieldOffset = @bitOffsetOf(Empty, "val",);
+        \\}
+    ,
+        ".tmp_source.zig:5:45: error: zero-bit field 'val' in struct 'Empty' has no offset",
     );
 
     cases.add(