atomic fixes and clarification

doc/langref.html.in

@@ -4356,7 +4356,7 @@ comptime {
       </p>
       <p>
       {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#}, a float,
-      an integer or an enum.
+      an integer, an enum, or a packed struct.
       </p>
       <p>{#syntax#}AtomicOrder{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicOrder{#endsyntax#}.</p>
       {#see_also|@atomicStore|@atomicRmw||@cmpxchgWeak|@cmpxchgStrong#}
@@ -4370,7 +4370,7 @@ comptime {
       </p>
       <p>
       {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#}, a float,
-      an integer or an enum.
+      an integer, an enum, or a packed struct.
       </p>
       <p>{#syntax#}AtomicOrder{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicOrder{#endsyntax#}.</p>
       <p>{#syntax#}AtomicRmwOp{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicRmwOp{#endsyntax#}.</p>
@@ -4384,7 +4384,7 @@ comptime {
       </p>
       <p>
       {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#}, a float,
-      an integer or an enum.
+      an integer, an enum, or a packed struct.
       </p>
       <p>{#syntax#}AtomicOrder{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicOrder{#endsyntax#}.</p>
       {#see_also|@atomicLoad|@atomicRmw|@cmpxchgWeak|@cmpxchgStrong#}
@@ -4613,8 +4613,8 @@ comptime {
       more efficiently in machine instructions.
       </p>
       <p>
-      {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#}, a float,
-      an integer or an enum.
+      {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#},
+      an integer, an enum, or a packed struct.
       </p>
       <p>{#syntax#}@typeInfo(@TypeOf(ptr)).pointer.alignment{#endsyntax#} must be {#syntax#}>= @sizeOf(T).{#endsyntax#}</p>
       <p>{#syntax#}AtomicOrder{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicOrder{#endsyntax#}.</p>
@@ -4645,8 +4645,8 @@ fn cmpxchgWeakButNotAtomic(comptime T: type, ptr: *T, expected_value: T, new_val
       However if you need a stronger guarantee, use {#link|@cmpxchgStrong#}.
       </p>
       <p>
-      {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#}, a float,
-      an integer or an enum.
+      {#syntax#}T{#endsyntax#} must be a pointer, a {#syntax#}bool{#endsyntax#},
+      an integer, an enum, or a packed struct.
       </p>
       <p>{#syntax#}@typeInfo(@TypeOf(ptr)).pointer.alignment{#endsyntax#} must be {#syntax#}>= @sizeOf(T).{#endsyntax#}</p>
       <p>{#syntax#}AtomicOrder{#endsyntax#} can be found with {#syntax#}@import("std").builtin.AtomicOrder{#endsyntax#}.</p>

src/Zcu.zig

@@ -3958,7 +3958,12 @@ pub fn atomicPtrAlignment(
         }
         return .none;
     }
-    if (ty.isAbiInt(zcu)) {
+    if (switch (ty.zigTypeTag(zcu)) {
+        .int, .@"enum" => true,
+        .@"struct" => ty.containerLayout(zcu) == .@"packed",
+        else => false,
+    }) {
+        assert(ty.isAbiInt(zcu));
         const bit_count = ty.intInfo(zcu).bits;
         if (bit_count > max_atomic_bits) {
             diags.* = .{

src/codegen/llvm.zig

@@ -4356,9 +4356,11 @@ pub const Object = struct {
     fn getAtomicAbiType(o: *Object, ty: Type, is_rmw_xchg: bool) Allocator.Error!Builder.Type {
         const pt = o.pt;
         const zcu = pt.zcu;
+        const ip = &zcu.intern_pool;
         const int_ty = switch (ty.zigTypeTag(zcu)) {
             .int => ty,
             .@"enum" => ty.intTagType(zcu),
+            .@"struct" => Type.fromInterned(ip.loadStructType(ty.toIntern()).backingIntTypeUnordered(ip)),
             .float => {
                 if (!is_rmw_xchg) return .none;
                 return o.builder.intType(@intCast(ty.abiSize(zcu) * 8));
@@ -11410,7 +11412,7 @@ pub const FuncGen = struct {
 
         if (workaround_disable_truncate) {
             // see https://github.com/llvm/llvm-project/issues/64222
-            // disable the truncation codepath for larger that 32bits value - with this heuristic, the backend passes the test suite.
+            // disable the truncation codepath for larger than 32bits value - with this heuristic, the backend passes the test suite.
             return try fg.wip.load(access_kind, payload_llvm_ty, payload_ptr, payload_alignment, "");
         }
 

test/behavior/atomics.zig

@@ -1,7 +1,6 @@
 const std = @import("std");
 const builtin = @import("builtin");
 const expect = std.testing.expect;
-const expectEqual = std.testing.expectEqual;
 
 const supports_128_bit_atomics = switch (builtin.cpu.arch) {
     // TODO: Ideally this could be sync'd with the logic in Sema.
@@ -362,25 +361,32 @@ test "atomics with different types" {
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_spirv) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
+    if (builtin.target.cpu.arch.endian() == .big) return error.SkipZigTest; // #24282
 
     try testAtomicsWithType(bool, true, false);
 
     try testAtomicsWithType(u1, 0, 1);
-    try testAtomicsWithType(i4, 0, 1);
-    try testAtomicsWithType(u5, 0, 1);
-    try testAtomicsWithType(i15, 0, 1);
-    try testAtomicsWithType(u24, 0, 1);
+    try testAtomicsWithType(i4, 2, 1);
+    try testAtomicsWithType(u5, 2, 1);
+    try testAtomicsWithType(i15, 2, 1);
+    try testAtomicsWithType(u24, 2, 1);
 
     try testAtomicsWithType(u0, 0, 0);
     try testAtomicsWithType(i0, 0, 0);
 
     try testAtomicsWithType(enum(u32) { x = 1234, y = 5678 }, .x, .y);
+    try testAtomicsWithType(enum(u19) { x = 1234, y = 5678 }, .x, .y);
 
     try testAtomicsWithPackedStruct(
         packed struct { x: u7, y: u24, z: bool },
         .{ .x = 1, .y = 2, .z = true },
         .{ .x = 3, .y = 4, .z = false },
     );
+    try testAtomicsWithPackedStruct(
+        packed struct { x: u19, y: bool },
+        .{ .x = 1, .y = true },
+        .{ .x = 3, .y = false },
+    );
 }
 
 fn testAtomicsWithType(comptime T: type, a: T, b: T) !void {

test/cases/compile_errors/atomics_with_invalid_type.zig

@@ -5,14 +5,27 @@ export fn float() void {
 
 const NormalStruct = struct { x: u32 };
 export fn normalStruct() void {
-    var x: NormalStruct = 0;
+    var x: NormalStruct = .{ .x = 0 };
     _ = @cmpxchgWeak(NormalStruct, &x, .{ .x = 1 }, .{ .x = 2 }, .seq_cst, .seq_cst);
 }
 
+export fn anyError() void {
+    var x: anyerror = error.A;
+    _ = @cmpxchgWeak(anyerror, &x, error.A, error.B, .seq_cst, .seq_cst);
+}
+
+const ErrorSet = error{ A, B };
+export fn errorSet() void {
+    var x: ErrorSet = error.A;
+    _ = @cmpxchgWeak(ErrorSet, &x, error.A, error.B, .seq_cst, .seq_cst);
+}
+
 // error
 // backend=stage2
 // target=native
 //
 // :3:22: error: expected bool, integer, enum, packed struct, or pointer type; found 'f32'
-// :8:27: error: expected type 'tmp.NormalStruct', found 'comptime_int'
+// :9:22: error: expected bool, integer, float, enum, packed struct, or pointer type; found 'tmp.NormalStruct'
 // :6:22: note: struct declared here
+// :14:22: error: expected bool, integer, float, enum, packed struct, or pointer type; found 'anyerror'
+// :20:22: error: expected bool, integer, float, enum, packed struct, or pointer type; found 'error{A,B}'