codegen: fix field offsets in packed structs

 * add nested packed struct/union behavior tests
 * use ptr_info.packed_offset rather than trying to duplicate the logic from Sema.structFieldPtrByIndex()
 * use the container_ptr_info.packed_offset to account for non-aligned nested structs.
 * dedup type.packedStructFieldBitOffset() and module.structPackedFieldBitOffset()

1 files changed, 2 insertions, 16 deletions

diff --git a/src/type.zig b/src/type.zig
index 79be8b4c5b..a7b760a482 100644
--- a/src/type.zig
+++ b/src/type.zig
@@ -3028,24 +3028,10 @@ pub const Type = struct {
         };
     }
 
-    pub fn packedStructFieldBitOffset(ty: Type, field_index: usize, mod: *Module) u32 {
+    pub fn packedStructFieldByteOffset(ty: Type, field_index: u32, mod: *Module) u32 {
         const ip = &mod.intern_pool;
         const struct_type = ip.indexToKey(ty.toIntern()).struct_type;
-        assert(struct_type.layout == .Packed);
-        comptime assert(Type.packed_struct_layout_version == 2);
-
-        var running_bits: u32 = 0;
-        for (struct_type.field_types.get(ip), 0..) |field_ty, i| {
-            if (i == field_index) break;
-            if (!field_ty.toType().hasRuntimeBits(mod)) continue;
-            const field_bits: u32 = @intCast(field_ty.toType().bitSize(mod));
-            running_bits += field_bits;
-        }
-        return running_bits;
-    }
-
-    pub fn packedStructFieldByteOffset(ty: Type, field_index: usize, mod: *Module) u32 {
-        return packedStructFieldBitOffset(ty, field_index, mod) / 8;
+        return @divExact(mod.structPackedFieldBitOffset(struct_type, field_index), 8);
     }
 
     pub const FieldOffset = struct {