From 7c5e3e1f8e4671b383865df0150b549e2445d170 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <superjoe30@gmail.com>
Date: Fri, 21 Sep 2018 14:15:58 -0400
Subject: [PATCH] fixups

---
 doc/langref.html.in              | 40 ++++++++++++++-------
 src/ir.cpp                       | 32 ++++++++++-------
 std/c/darwin.zig                 | 26 +++++++-------
 test/cases/sizeof_and_typeof.zig | 61 +++++++++++++++++++++-----------
 test/compile_errors.zig          |  8 ++---
 5 files changed, 104 insertions(+), 63 deletions(-)

diff --git a/doc/langref.html.in b/doc/langref.html.in
index ef37d657dc..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>
@@ -5145,6 +5166,13 @@ fn seq(c: u8) void {
       This function is only valid within function scope.
       </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>
@@ -5868,18 +5896,6 @@ fn add(a: i32, b: i32) i32 {
       </p>
       {#see_also|@inlineCall#}
       {#header_close#}
-      {#header_open|@offsetOf#}
-      <pre>{#syntax#}@byteOffsetOf(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|@bitOffsetOf#}
-      <pre><code class="zig">@bitOffsetOf(comptime T: type, comptime field_name: [] const u8) (number literal)</code></pre>
-      <p>
-      This function returns the bit 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/ir.cpp b/src/ir.cpp
index 7daff2ca0e..5e0f79ec13 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -17088,30 +17088,36 @@ 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)) {
-        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;
-    }
-    return ira->codegen->builtin_types.entry_invalid;
+    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))) {
-        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;
-    }
-    return ira->codegen->builtin_types.entry_invalid;
+    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)
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 2d1ffa9434..11c6b2f6ba 100644
--- a/test/cases/sizeof_and_typeof.zig
+++ b/test/cases/sizeof_and_typeof.zig
@@ -1,13 +1,14 @@
+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);
 }
 const x: u16 = 13;
 const z: @typeOf(x) = 19;
 
-const S = struct {
+const A = struct {
     a: u8,
     b: u32,
     c: u8,
@@ -27,24 +28,42 @@ const P = packed struct {
     g: u16,
 };
 
-test "byteOffsetOf" {
-    const p: P = undefined;
-    std.debug.assert(@byteOffsetOf(P, "a") == 0 and @byteOffsetOf(S, "a") == 0);
-    std.debug.assert(@byteOffsetOf(P, "b") == 1 and @byteOffsetOf(S, "b") == 4);
-    std.debug.assert(@byteOffsetOf(P, "c") == 5 and @byteOffsetOf(S, "c") == 8);
-    std.debug.assert(@byteOffsetOf(P, "d") == 6 and @byteOffsetOf(S, "d") == 9);
-    std.debug.assert(@byteOffsetOf(P, "e") == 6 and @byteOffsetOf(S, "e") == 10);
-    std.debug.assert(@byteOffsetOf(P, "f") == 7 and @byteOffsetOf(S, "f") == 12);
-    std.debug.assert(@byteOffsetOf(P, "g") == 9 and @byteOffsetOf(S, "g") == 14);
+test "@byteOffsetOf" {
+    // Packed structs have fixed memory layout
+    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);
+
+    // 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" {
-    const p: P = undefined;
-    std.debug.assert(@bitOffsetOf(P, "a") == 0 and @bitOffsetOf(S, "a") == 0);
-    std.debug.assert(@bitOffsetOf(P, "b") == 8 and @bitOffsetOf(S, "b") == 32);
-    std.debug.assert(@bitOffsetOf(P, "c") == 40 and @bitOffsetOf(S, "c") == 64);
-    std.debug.assert(@bitOffsetOf(P, "d") == 48 and @bitOffsetOf(S, "d") == 72);
-    std.debug.assert(@bitOffsetOf(P, "e") == 51 and @bitOffsetOf(S, "e") == 80);
-    std.debug.assert(@bitOffsetOf(P, "f") == 56 and @bitOffsetOf(S, "f") == 96);
-    std.debug.assert(@bitOffsetOf(P, "g") == 72 and @bitOffsetOf(S, "g") == 112);
-}
\ No newline at end of file
+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 7b659a8dc1..fae022f3fb 100644
--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -3769,7 +3769,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         \\    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(
@@ -3781,7 +3781,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         \\    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(
@@ -5092,7 +5092,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         \\    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(
@@ -5104,7 +5104,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         \\    const fieldOffset = @bitOffsetOf(Empty, "val",);
         \\}
     ,
-        ".tmp_source.zig:5:42: error: zero-bit field 'val' in struct 'Empty' has no offset",
+        ".tmp_source.zig:5:45: error: zero-bit field 'val' in struct 'Empty' has no offset",
     );
 
     cases.add(