storage manager: preserve upper address bits on 64bit machines (thanks to zygoloid)

the issue: durin ia64 ghc bootstrap (both 6.10.4 and 6.12.3) I
got the failure on stage2 phase:
    "inplace/bin/ghc-stage2"   -H32m -O -H64m -O0 -w ...
    ghc-stage2: internal error: evacuate: strange closure type 15
        (GHC version 6.12.3 for ia64_unknown_linux)
        Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
    make[1]: *** [libraries/dph/dph-base/dist-install/build/Data/Array/Parallel/Base/Hyperstrict.o] Aborted

I attached gdb and got backtrace:

Breakpoint 1 at 0x400000000469ec31: file rts/RtsMessages.c, line 39.
(gdb) run -B/var/tmp/portage/dev-lang/ghc-6.12.3/work/ghc-6.12.3/inplace/bin --info
Starting program: /var/tmp/portage/dev-lang/ghc-6.12.3/work/ghc-6.12.3/inplace/lib/ghc-stage2 -B/var/tmp/portage/dev-lang/ghc-6.12.3/work/ghc-6.12.3/inplace/bin --info
[Thread debugging using libthread_db enabled]

Breakpoint 1, barf (s=0x40000000047915b0 "evacuate: strange closure type %d") at rts/RtsMessages.c:39
39        va_start(ap,s);
(gdb) bt
#0  barf (s=0x40000000047915b0 "evacuate: strange closure type %d") at rts/RtsMessages.c:39
#1  0x400000000474a1e0 in evacuate (p=0x6000000000147958) at rts/sm/Evac.c:756
#2  0x40000000046d68c0 in scavenge_srt (srt=0x6000000000147958, srt_bitmap=7) at rts/sm/Scav.c:348
...

> 16:52:53 < zygoloid> slyfox: i'm no ghc expert but it looks like HEAP_ALLOCED_GC(q)
>                      is returning true for a FUN_STATIC closure
> 17:18:43 < zygoloid> try: p HEAP_ALLOCED_miss((unsigned long)(*p) >> 20, *p)
> 17:19:12 < slyfox> (gdb) p HEAP_ALLOCED_miss((unsigned long)(*p) >> 20, *p)
> 17:19:12 < slyfox> $1 = 0
> 17:19:40 < zygoloid> i /think/ that means the mblock_cache is broken
> 17:22:45 < zygoloid> i can't help further. however i am suspicious that you seem to have pointers with similar-looking low 33 
>                      bits and different high 4 bits, and it looks like such pointers get put into the same bucket in 
>                      mblock_cache.
...
> 17:36:16 < zygoloid> slyfox: try changing the definition of MbcCacheLine to StgWord64, see if that helps
> 17:36:31 < zygoloid> that's in includes/rts/storage/MBlock.h
And it helped!

diff --git a/includes/rts/storage/MBlock.h b/includes/rts/storage/MBlock.h
index 0943d4c..a113498 100644
--- a/includes/rts/storage/MBlock.h
+++ b/includes/rts/storage/MBlock.h
@@ -126,7 +126,17 @@ extern StgWord8 mblock_map[];
 
 #define MBC_LINE_BITS 0
 #define MBC_TAG_BITS 15
-typedef StgWord32 MbcCacheLine;  // could use 16, but 32 was faster
+
+#if x86_64_HOST_ARCH
+// 32bits are enough for 'entry' as modern amd64 boxes have
+// only 48bit sized virtual addres.
+typedef StgWord32 MbcCacheLine;
+#else
+// 32bits is not enough here as some arches (like ia64) use
+// upper address bits to distinct memory areas.
+typedef StgWord64 MbcCacheLine;
+#endif
+
 typedef StgWord8  MBlockMapLine;
 
 #define MBLOCK_MAP_LINE(p)  (((StgWord)p & 0xffffffff) >> (MBLOCK_SHIFT + MBC_LINE_BITS))