[MLton] share bug

[Henry Cejtin]

One  strange  thing I meant to remark on before I put your patch in: the word
`maybeSharePointer' NEVER appears in the stderr output.  This means, from  my
reading  of gc.c, that maybeSharePointer was never called with shouldHashCons
true.  Sorry, I see now that your fix was only to that code.  I don't get why
it  was never called with the flag true, because certainly there are pointers
to non-mutable objects (strings) which should be shared.

Unrelated to that, and not understanding perfectly what the card being marked
for  a location says, when you replace a reference to p with one for q, don't
you have to or in the marks on p into those for q.

Any way, here is the lines around the start of GC_share:

    About to start doGC()
    GC state
            cardMap = 0x401ae000
            oldGen = 0x600b2000
            oldGenSize = 895,933,492
            oldGen + oldGenSize = 0x9571fc34
            nursery = 0x9a6f4e1c
            frontier = 0x9f6c9e08
            frontier - nursery = 83709932
            limitPlusSlop - frontier = 504
            canHandle = 1
            signalsIsPending = 0
            currentThread = 0x600b31dc
            stackBottom = 0x690375cc
            stackTop - stackBottom = 136
            stackLimit - stackTop = 408
            exnStack = 8
            bytesNeeded = 512
            reserved = 800
            used = 136
    Starting gc.  Request 512 nursery bytes and 0 old gen bytes.
    Minor GC.
    Minor GC done.  441,124 bytes copied.
    Finished gc.
    time: 7,080 ms
    old gen size: 896,374,616 bytes (84.3%)
    About to leave doGC()
    GC state
            cardMap = 0x401ae000
            oldGen = 0x600b2000
            oldGenSize = 896,374,616
            oldGen + oldGenSize = 0x9578b758
            nursery = 0x9a72abac
            frontier = 0x9a72abac
            frontier - nursery = 0
            limitPlusSlop - frontier = 83489876
            canHandle = 1
            signalsIsPending = 0
            currentThread = 0x600b31dc
            stackBottom = 0x690375cc
            stackTop - stackBottom = 136
            stackLimit - stackTop = 408
            exnStack = 8
            bytesNeeded = 512
            reserved = 800
            used = 136
    Done reading
    GC_share 0x600b3398
    GC state
            cardMap = 0x401ae000
            oldGen = 0x600b2000
            oldGenSize = 896,374,616
            oldGen + oldGenSize = 0x9578b758
            nursery = 0x9a72abac
            frontier = 0x9e0b2c64
            frontier - nursery = 60326072
            limitPlusSlop - frontier = 23163804
            canHandle = 0
            signalsIsPending = 0
            currentThread = 0x600b31dc
            stackBottom = 0x690375cc
            stackTop - stackBottom = 140
            stackLimit - stackTop = 404
            exnStack = 8
            bytesNeeded = 512
            reserved = 800
            used = 136
    using minor space
    maxElementsSize = 10436234
    elementsIsInHeap = TRUE
    elementsSize = 8388608
    0x08074018 = newTable ()
    hashCons (0x600ba678)
    0x600ba678 = hashCons (0x600ba678)
    hashCons (0x600ba680)
    0x600ba680 = hashCons (0x600ba680)
    hashCons (0x68d8d808)
    tableInsert (3941444285, 0x68d8d808, TRUE, 0x00000003, 0x68d8d814)
    probe = 0x0038075b
    slot = 0x0038075b
    numProbes = 1
    0x68d8d808 = hashCons (0x68d8d808)

and here are the lines around the end:

    0x600ba594 = hashCons (0x600ba594)
    hashCons (0x600b5268)
    0x600b5268 = hashCons (0x600b5268)
    hashCons (0x600b3398)
    tableInsert (368121331, 0x600b3398, TRUE, 0x00000055, 0x600b367c)
    probe = 0x01ff36dd
    slot = 0x01ff36de
    slot = 0x03fe6dbb
    0x600b3398 = hashCons (0x600b3398)
    GC state
            cardMap = 0x401ae000
            oldGen = 0x600b2000
            oldGenSize = 896,374,616
            oldGen + oldGenSize = 0x9578b758
            nursery = 0x9a72abac
            frontier = 0x9e0b2c64
            frontier - nursery = 60326072
            limitPlusSlop - frontier = 23163804
            canHandle = 0
            signalsIsPending = 0
            currentThread = 0x600b31dc
            stackBottom = 0x690375cc
            stackTop - stackBottom = 140
            stackLimit - stackTop = 404
            exnStack = 8
            bytesNeeded = 512
            reserved = 800
            used = 136
    32,016,852 bytes hash consed (5.7%).
    About to start doGC()
    GC state
            cardMap = 0x401ae000
            oldGen = 0x600b2000
            oldGenSize = 896,374,616
            oldGen + oldGenSize = 0x9578b758
            nursery = 0x9a72abac
            frontier = 0x9e0b3bfc
            frontier - nursery = 60330064
            limitPlusSlop - frontier = 23159812
            canHandle = 1
            signalsIsPending = 0
            currentThread = 0x600b31dc
            stackBottom = 0x690375cc
            stackTop - stackBottom = 160
            stackLimit - stackTop = 384
            exnStack = 8
            bytesNeeded = 512
            reserved = 800
            used = 160
    Starting gc.  Request 0 nursery bytes and 4,000,012 old gen bytes.
    Minor GC.
    Minor GC done.  294,392 bytes copied.
    Finished gc.
    time: 6,690 ms
    old gen size: 896,669,008 bytes (84.3%)
    gc.c: assertIsInFromSpace p = 0x665aeab4  *p = 0x9ac95540);

Just before the call to share it  computed  the  size  of  the  object  being
shared, and it was
    561,950,212 bytes

Just after it computed the size and it was
    529,933,360 bytes
just  like  before.  The latter must have been done before the first minor GC
was needed.