code review 112570044: cmd/gc, runtime: treat slices and strings like pointers...

src/pkg/runtime/mgc0.h

 // Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Garbage collector (GC)
 
 enum {
         ScanStackByFrames = 1,
 
         // Four bits per word (see #defines below).
@@ skipping 32 matching lines @@
         BitsPerPointer  = 2,
         BitsMask        = (1<<BitsPerPointer)-1,
         PointersPerByte = 8/BitsPerPointer,
 
         BitsDead        = 0,
         BitsScalar      = 1,
         BitsPointer     = 2,
         BitsMultiWord   = 3,
         // BitsMultiWord will be set for the first word of a multi-word item.
         // When it is set, one of the following will be set for the second word.
-        BitsString      = 0,
-        BitsSlice       = 1,
+        // NOT USED ANYMORE: BitsString = 0,
+        // NOT USED ANYMORE: BitsSlice  = 1,
         BitsIface       = 2,
         BitsEface       = 3,
 
         // 64 bytes cover objects of size 1024/512 on 64/32 bits, respectively.
         MaxGCMask       = 64,
 };
 
 // Bits in per-word bitmap.
 // #defines because we shift the values beyond 32 bits.
 //
 // Each word in the bitmap describes wordsPerBitmapWord words
 // of heap memory.  There are 4 bitmap bits dedicated to each heap word,
 // so on a 64-bit system there is one bitmap word per 16 heap words.
 //
 // The bitmap starts at mheap.arena_start and extends *backward* from
 // there.  On a 64-bit system the off'th word in the arena is tracked by
 // the off/16+1'th word before mheap.arena_start.  (On a 32-bit system,
 // the only difference is that the divisor is 8.)
 
 #define bitBoundary     ((uintptr)1) // boundary of an object
 #define bitMarked       ((uintptr)2) // marked object
 
 #define bitMask         ((uintptr)bitBoundary|bitMarked)
 #define bitPtrMask      ((uintptr)BitsMask<<2)