refactor bitfields

Use 2 level strategy to access packed bitfields cleanly:

1) Allow to override the original declaration type with
   an auxilary "access type".  This solves cases such as

    struct {
        ...
        unsigned f1:1;
    };

    by using VT_BYTE to access f1.

2) Allow byte-wise split accesses using two new functions
   load/store_packed_bf. This solves any cases, also ones
   such as

    struct __attribute((packed)) _s {
        unsigned x : 12;
        unsigned char y : 7;
        unsigned z : 28;
        unsigned a: 3;
        unsigned b: 3;
        unsigned c: 3;
    };

    where for field 'z':
    - VT_INT access from offset 2 would be unaligned
    - VT_LLONG from offset 0 would go past the total
      struct size (7)

    and for field 'a' because it is in two bytes and
    aligned access with VT_SHORT/INT is not possible.

Also, static bitfield initializers are stored byte-wise always.
Also, cleanup the struct_layout function a bit.

1 files changed, 4 insertions, 4 deletions

diff --git a/tests/tcctest.c b/tests/tcctest.c
index bc08968..10203ec 100644
--- a/tests/tcctest.c
+++ b/tests/tcctest.c
@@ -1050,8 +1050,8 @@ int pad1;
    but __alignof__ returns the wrong result (4) because we
    can't store the alignment yet when specified on symbols
    directly (it's stored in the type so we'd need to make
-   a copy of it).
-struct aligntest7 altest7[2] __attribute__((aligned(16)));*/
+   a copy of it). -- FIXED */
+struct aligntest7 altest7[2] __attribute__((aligned(16)));
 
 struct aligntest8
 {
@@ -1161,8 +1161,8 @@ void struct_test()
            sizeof(altest5), __alignof__(altest5));
     printf("altest6 sizeof=%d alignof=%d\n",
            sizeof(altest6), __alignof__(altest6));
-    /*printf("altest7 sizeof=%d alignof=%d\n",
-           sizeof(altest7), __alignof__(altest7));*/
+    printf("altest7 sizeof=%d alignof=%d\n",
+           sizeof(altest7), __alignof__(altest7));
            
     /* empty structures (GCC extension) */
     printf("sizeof(struct empty) = %d\n", sizeof(struct empty));