Sema: automatically optimize order of struct fields

This is a simple starting version of the optimization described in #168
where the fields are just sorted by order of descending alignment.

1 files changed, 18 insertions, 0 deletions

diff --git a/test/behavior/struct.zig b/test/behavior/struct.zig
index 20a09f92cc..a32a0ed495 100644
--- a/test/behavior/struct.zig
+++ b/test/behavior/struct.zig
@@ -1555,3 +1555,21 @@ test "optional generic function label struct field" {
     };
     try expect((Options{}).isFoo.?(u8) == 123);
 }
+
+test "struct fields get automatically reordered" {
+    if (builtin.zig_backend != .stage2_llvm) return error.SkipZigTest; // TODO
+
+    const S1 = struct {
+        a: u32,
+        b: u32,
+        c: bool,
+        d: bool,
+    };
+    const S2 = struct {
+        a: u32,
+        b: bool,
+        c: u32,
+        d: bool,
+    };
+    try expect(@sizeOf(S1) == @sizeOf(S2));
+}