x86_64: fix packed struct equality

Closes #22990

Author: jacobly0

src/arch/x86_64/CodeGen.zig

@@ -77309,11 +77309,27 @@ fn genBody(cg: *CodeGen, body: []const Air.Inst.Index) InnerError!void {
                             },
                         }
                     },
-                    .int => res[0] = ops[0].cmpInts(cmp_op, &ops[1], cg) catch |err| break :err err,
+                    .int => {
+                        switch (ty.zigTypeTag(zcu)) {
+                            else => {},
+                            .@"struct", .@"union" => {
+                                assert(ty.containerLayout(zcu) == .@"packed");
+                                for (&ops) |*op| op.wrapInt(cg) catch |err| switch (err) {
+                                    error.SelectFailed => return cg.fail("failed to select {s} wrap {} {}", .{
+                                        @tagName(air_tag),
+                                        ty.fmt(pt),
+                                        op.tracking(cg),
+                                    }),
+                                    else => |e| return e,
+                                };
+                            },
+                        }
+                        res[0] = ops[0].cmpInts(cmp_op, &ops[1], cg) catch |err| break :err err;
+                    },
                 }) catch |err| switch (err) {
                     error.SelectFailed => return cg.fail("failed to select {s} {} {} {}", .{
                         @tagName(air_tag),
-                        cg.typeOf(bin_op.lhs).fmt(pt),
+                        ty.fmt(pt),
                         ops[0].tracking(cg),
                         ops[1].tracking(cg),
                     }),

test/behavior/packed-struct.zig

@@ -1307,6 +1307,17 @@ test "packed struct equality" {
     comptime try S.doTest(x, y);
 }
 
+test "packed struct equality ignores padding bits" {
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_spirv64) return error.SkipZigTest;
+
+    const S = packed struct { b: bool };
+    var s: S = undefined;
+    s.b = true;
+    try std.testing.expect(s != S{ .b = false });
+    try std.testing.expect(s == S{ .b = true });
+}
+
 test "packed struct with signed field" {
     var s: packed struct {
         a: i2,