--- a/hotspot/src/cpu/aarch64/vm/aarch64.ad Mon Feb 22 08:04:12 2016 +0100
+++ b/hotspot/src/cpu/aarch64/vm/aarch64.ad Mon Feb 15 10:14:33 2016 +0100
@@ -1041,10 +1041,8 @@
bool is_card_mark_membar(const MemBarNode *barrier);
bool is_CAS(int opcode);
- MemBarNode *leading_to_normal(MemBarNode *leading);
- MemBarNode *normal_to_leading(const MemBarNode *barrier);
- MemBarNode *card_mark_to_trailing(const MemBarNode *barrier);
- MemBarNode *trailing_to_card_mark(const MemBarNode *trailing);
+ MemBarNode *leading_to_trailing(MemBarNode *leading);
+ MemBarNode *card_mark_to_leading(const MemBarNode *barrier);
MemBarNode *trailing_to_leading(const MemBarNode *trailing);
// predicates controlling emit of ldr<x>/ldar<x> and associated dmb
@@ -1418,23 +1416,28 @@
// leading MemBarRelease and a trailing MemBarVolatile as follows
//
// MemBarRelease
- // { || } -- optional
+ // { || } -- optional
// {MemBarCPUOrder}
- // || \\
- // || StoreX[mo_release]
- // | \ /
- // | MergeMem
- // | /
+ // || \\
+ // || StoreX[mo_release]
+ // | \ Bot / ???
+ // | MergeMem
+ // | /
// MemBarVolatile
//
// where
// || and \\ represent Ctl and Mem feeds via Proj nodes
// | \ and / indicate further routing of the Ctl and Mem feeds
//
- // this is the graph we see for non-object stores. however, for a
- // volatile Object store (StoreN/P) we may see other nodes below the
- // leading membar because of the need for a GC pre- or post-write
- // barrier.
+ // Note that the memory feed from the CPUOrder membar to the
+ // MergeMem node is an AliasIdxBot slice while the feed from the
+ // StoreX is for a slice determined by the type of value being
+ // written.
+ //
+ // the diagram above shows the graph we see for non-object stores.
+ // for a volatile Object store (StoreN/P) we may see other nodes
+ // below the leading membar because of the need for a GC pre- or
+ // post-write barrier.
//
// with most GC configurations we with see this simple variant which
// includes a post-write barrier card mark.
@@ -1442,7 +1445,7 @@
// MemBarRelease______________________________
// || \\ Ctl \ \\
// || StoreN/P[mo_release] CastP2X StoreB/CM
- // | \ / . . . /
+ // | \ Bot / oop . . . /
// | MergeMem
// | /
// || /
@@ -1452,152 +1455,142 @@
// the object address to an int used to compute the card offset) and
// Ctl+Mem to a StoreB node (which does the actual card mark).
//
- // n.b. a StoreCM node will only appear in this configuration when
- // using CMS. StoreCM differs from a normal card mark write (StoreB)
- // because it implies a requirement to order visibility of the card
- // mark (StoreCM) relative to the object put (StoreP/N) using a
- // StoreStore memory barrier (arguably this ought to be represented
- // explicitly in the ideal graph but that is not how it works). This
- // ordering is required for both non-volatile and volatile
- // puts. Normally that means we need to translate a StoreCM using
- // the sequence
+ // n.b. a StoreCM node is only ever used when CMS (with or without
+ // CondCardMark) or G1 is configured. This abstract instruction
+ // differs from a normal card mark write (StoreB) because it implies
+ // a requirement to order visibility of the card mark (StoreCM)
+ // after that of the object put (StoreP/N) using a StoreStore memory
+ // barrier. Note that this is /not/ a requirement to order the
+ // instructions in the generated code (that is already guaranteed by
+ // the order of memory dependencies). Rather it is a requirement to
+ // ensure visibility order which only applies on architectures like
+ // AArch64 which do not implement TSO. This ordering is required for
+ // both non-volatile and volatile puts.
+ //
+ // That implies that we need to translate a StoreCM using the
+ // sequence
//
// dmb ishst
// stlrb
//
- // However, in the case of a volatile put if we can recognise this
- // configuration and plant an stlr for the object write then we can
- // omit the dmb and just plant an strb since visibility of the stlr
- // is ordered before visibility of subsequent stores. StoreCM nodes
- // also arise when using G1 or using CMS with conditional card
- // marking. In these cases (as we shall see) we don't need to insert
- // the dmb when translating StoreCM because there is already an
- // intervening StoreLoad barrier between it and the StoreP/N.
- //
- // It is also possible to perform the card mark conditionally on it
- // currently being unmarked in which case the volatile put graph
- // will look slightly different
+ // This dmb cannot be omitted even when the associated StoreX or
+ // CompareAndSwapX is implemented using stlr. However, as described
+ // below there are circumstances where a specific GC configuration
+ // requires a stronger barrier in which case it can be omitted.
+ //
+ // With the Serial or Parallel GC using +CondCardMark the card mark
+ // is performed conditionally on it currently being unmarked in
+ // which case the volatile put graph looks slightly different
//
// MemBarRelease____________________________________________
// || \\ Ctl \ Ctl \ \\ Mem \
// || StoreN/P[mo_release] CastP2X If LoadB |
- // | \ / \ |
+ // | \ Bot / oop \ |
// | MergeMem . . . StoreB
// | / /
// || /
// MemBarVolatile
//
- // It is worth noting at this stage that both the above
+ // It is worth noting at this stage that all the above
// configurations can be uniquely identified by checking that the
// memory flow includes the following subgraph:
//
// MemBarRelease
// {MemBarCPUOrder}
- // | \ . . .
- // | StoreX[mo_release] . . .
- // | /
- // MergeMem
- // |
+ // | \ . . .
+ // | StoreX[mo_release] . . .
+ // Bot | / oop
+ // MergeMem
+ // |
// MemBarVolatile
//
- // This is referred to as a *normal* subgraph. It can easily be
- // detected starting from any candidate MemBarRelease,
- // StoreX[mo_release] or MemBarVolatile.
- //
- // A simple variation on this normal case occurs for an unsafe CAS
- // operation. The basic graph for a non-object CAS is
+ // This is referred to as a *normal* volatile store subgraph. It can
+ // easily be detected starting from any candidate MemBarRelease,
+ // StoreX[mo_release] or MemBarVolatile node.
+ //
+ // A small variation on this normal case occurs for an unsafe CAS
+ // operation. The basic memory flow subgraph for a non-object CAS is
+ // as follows
//
// MemBarRelease
// ||
// MemBarCPUOrder
- // || \\ . . .
- // || CompareAndSwapX
- // || |
- // || SCMemProj
- // | \ /
- // | MergeMem
- // | /
+ // | \\ . . .
+ // | CompareAndSwapX
+ // | |
+ // Bot | SCMemProj
+ // \ / Bot
+ // MergeMem
+ // /
// MemBarCPUOrder
// ||
// MemBarAcquire
//
// The same basic variations on this arrangement (mutatis mutandis)
- // occur when a card mark is introduced. i.e. we se the same basic
- // shape but the StoreP/N is replaced with CompareAndSawpP/N and the
- // tail of the graph is a pair comprising a MemBarCPUOrder +
- // MemBarAcquire.
- //
- // So, in the case of a CAS the normal graph has the variant form
- //
- // MemBarRelease
- // MemBarCPUOrder
- // | \ . . .
- // | CompareAndSwapX . . .
- // | |
- // | SCMemProj
- // | / . . .
- // MergeMem
- // |
- // MemBarCPUOrder
- // MemBarAcquire
- //
- // This graph can also easily be detected starting from any
- // candidate MemBarRelease, CompareAndSwapX or MemBarAcquire.
- //
- // the code below uses two helper predicates, leading_to_normal and
- // normal_to_leading to identify these normal graphs, one validating
- // the layout starting from the top membar and searching down and
- // the other validating the layout starting from the lower membar
- // and searching up.
- //
- // There are two special case GC configurations when a normal graph
- // may not be generated: when using G1 (which always employs a
- // conditional card mark); and when using CMS with conditional card
- // marking configured. These GCs are both concurrent rather than
- // stop-the world GCs. So they introduce extra Ctl+Mem flow into the
- // graph between the leading and trailing membar nodes, in
- // particular enforcing stronger memory serialisation beween the
- // object put and the corresponding conditional card mark. CMS
- // employs a post-write GC barrier while G1 employs both a pre- and
- // post-write GC barrier. Of course the extra nodes may be absent --
- // they are only inserted for object puts. This significantly
- // complicates the task of identifying whether a MemBarRelease,
- // StoreX[mo_release] or MemBarVolatile forms part of a volatile put
- // when using these GC configurations (see below). It adds similar
- // complexity to the task of identifying whether a MemBarRelease,
- // CompareAndSwapX or MemBarAcquire forms part of a CAS.
- //
- // In both cases the post-write subtree includes an auxiliary
- // MemBarVolatile (StoreLoad barrier) separating the object put and
- // the read of the corresponding card. This poses two additional
- // problems.
- //
- // Firstly, a card mark MemBarVolatile needs to be distinguished
- // from a normal trailing MemBarVolatile. Resolving this first
- // problem is straightforward: a card mark MemBarVolatile always
- // projects a Mem feed to a StoreCM node and that is a unique marker
+ // occur when a card mark is introduced. i.e. the CPUOrder MemBar
+ // feeds the extra CastP2X, LoadB etc nodes but the above memory
+ // flow subgraph is still present.
+ //
+ // This is referred to as a *normal* CAS subgraph. It can easily be
+ // detected starting from any candidate MemBarRelease,
+ // StoreX[mo_release] or MemBarAcquire node.
+ //
+ // The code below uses two helper predicates, leading_to_trailing
+ // and trailing_to_leading to identify these normal graphs, one
+ // validating the layout starting from the top membar and searching
+ // down and the other validating the layout starting from the lower
+ // membar and searching up.
+ //
+ // There are two special case GC configurations when the simple
+ // normal graphs above may not be generated: when using G1 (which
+ // always employs a conditional card mark); and when using CMS with
+ // conditional card marking (+CondCardMark) configured. These GCs
+ // are both concurrent rather than stop-the world GCs. So they
+ // introduce extra Ctl+Mem flow into the graph between the leading
+ // and trailing membar nodes, in particular enforcing stronger
+ // memory serialisation beween the object put and the corresponding
+ // conditional card mark. CMS employs a post-write GC barrier while
+ // G1 employs both a pre- and post-write GC barrier.
+ //
+ // The post-write barrier subgraph for these configurations includes
+ // a MemBarVolatile node -- referred to as a card mark membar --
+ // which is needed to order the card write (StoreCM) operation in
+ // the barrier, the preceding StoreX (or CompareAndSwapX) and Store
+ // operations performed by GC threads i.e. a card mark membar
+ // constitutes a StoreLoad barrier hence must be translated to a dmb
+ // ish (whether or not it sits inside a volatile store sequence).
+ //
+ // Of course, the use of the dmb ish for the card mark membar also
+ // implies theat the StoreCM which follows can omit the dmb ishst
+ // instruction. The necessary visibility ordering will already be
+ // guaranteed by the dmb ish. In sum, the dmb ishst instruction only
+ // needs to be generated for as part of the StoreCM sequence with GC
+ // configuration +CMS -CondCardMark.
+ //
+ // Of course all these extra barrier nodes may well be absent --
+ // they are only inserted for object puts. Their potential presence
+ // significantly complicates the task of identifying whether a
+ // MemBarRelease, StoreX[mo_release], MemBarVolatile or
+ // MemBarAcquire forms part of a volatile put or CAS when using
+ // these GC configurations (see below) and also complicates the
+ // decision as to how to translate a MemBarVolatile and StoreCM.
+ //
+ // So, thjis means that a card mark MemBarVolatile occurring in the
+ // post-barrier graph it needs to be distinguished from a normal
+ // trailing MemBarVolatile. Resolving this is straightforward: a
+ // card mark MemBarVolatile always projects a Mem feed to a StoreCM
+ // node and that is a unique marker
//
// MemBarVolatile (card mark)
// C | \ . . .
// | StoreCM . . .
// . . .
//
- // The second problem is how the code generator is to translate the
- // card mark barrier? It always needs to be translated to a "dmb
- // ish" instruction whether or not it occurs as part of a volatile
- // put. A StoreLoad barrier is needed after the object put to ensure
- // i) visibility to GC threads of the object put and ii) visibility
- // to the mutator thread of any card clearing write by a GC
- // thread. Clearly a normal store (str) will not guarantee this
- // ordering but neither will a releasing store (stlr). The latter
- // guarantees that the object put is visible but does not guarantee
- // that writes by other threads have also been observed.
- //
- // So, returning to the task of translating the object put and the
- // leading/trailing membar nodes: what do the non-normal node graph
- // look like for these 2 special cases? and how can we determine the
- // status of a MemBarRelease, StoreX[mo_release] or MemBarVolatile
- // in both normal and non-normal cases?
+ // Returning to the task of translating the object put and the
+ // leading/trailing membar nodes: what do the node graphs look like
+ // for these 2 special cases? and how can we determine the status of
+ // a MemBarRelease, StoreX[mo_release] or MemBarVolatile in both
+ // normal and non-normal cases?
//
// A CMS GC post-barrier wraps its card write (StoreCM) inside an If
// which selects conditonal execution based on the value loaded
@@ -1608,91 +1601,117 @@
// which looks like this
//
// MemBarRelease
- // MemBarCPUOrder_(leading)__________________
- // C | M \ \\ C \
- // | \ StoreN/P[mo_release] CastP2X
- // | Bot \ /
- // | MergeMem
- // | /
- // MemBarVolatile (card mark)
- // C | || M |
- // | LoadB |
- // | | |
- // | Cmp |\
- // | / | \
- // If | \
- // | \ | \
- // IfFalse IfTrue | \
- // \ / \ | \
- // \ / StoreCM |
- // \ / | |
- // Region . . . |
- // | \ /
- // | . . . \ / Bot
+ // MemBarCPUOrder_(leading)____________________
+ // C | | M \ \\ M | C \
+ // | | \ StoreN/P[mo_release] | CastP2X
+ // | | Bot \ / oop \ |
+ // | | MergeMem \ /
+ // | | / | /
+ // MemBarVolatile (card mark) | /
+ // C | || M | | /
+ // | LoadB | Bot oop | / Bot
+ // | | | / /
+ // | Cmp |\ / /
+ // | / | \ / /
+ // If | \ / /
+ // | \ | \ / /
+ // IfFalse IfTrue | \ / /
+ // \ / \ | | / /
+ // \ / StoreCM | / /
+ // \ / \ / / /
+ // Region Phi / /
+ // | \ Raw | / /
+ // | . . . | / /
// | MergeMem
- // | |
+ // | |
// MemBarVolatile (trailing)
//
- // The first MergeMem merges the AliasIdxBot Mem slice from the
- // leading membar and the oopptr Mem slice from the Store into the
- // card mark membar. The trailing MergeMem merges the AliasIdxBot
- // Mem slice from the card mark membar and the AliasIdxRaw slice
- // from the StoreCM into the trailing membar (n.b. the latter
- // proceeds via a Phi associated with the If region).
- //
- // The graph for a CAS varies slightly, the obvious difference being
- // that the StoreN/P node is replaced by a CompareAndSwapP/N node
- // and the trailing MemBarVolatile by a MemBarCPUOrder +
- // MemBarAcquire pair. The other important difference is that the
- // CompareAndSwap node's SCMemProj is not merged into the card mark
- // membar - it still feeds the trailing MergeMem. This also means
- // that the card mark membar receives its Mem feed directly from the
- // leading membar rather than via a MergeMem.
+ // Notice that there are two MergeMem nodes below the leading
+ // membar. The first MergeMem merges the AliasIdxBot Mem slice from
+ // the leading membar and the oopptr Mem slice from the Store into
+ // the card mark membar. The trailing MergeMem merges the
+ // AliasIdxBot Mem slice from the leading membar, the AliasIdxRaw
+ // slice from the StoreCM and an oop slice from the StoreN/P node
+ // into the trailing membar (n.b. the raw slice proceeds via a Phi
+ // associated with the If region).
+ //
+ // So, in the case of CMS + CondCardMark the volatile object store
+ // graph still includes a normal volatile store subgraph from the
+ // leading membar to the trailing membar. However, it also contains
+ // the same shape memory flow to the card mark membar. The two flows
+ // can be distinguished by testing whether or not the downstream
+ // membar is a card mark membar.
+ //
+ // The graph for a CAS also varies with CMS + CondCardMark, in
+ // particular employing a control feed from the CompareAndSwapX node
+ // through a CmpI and If to the card mark membar and StoreCM which
+ // updates the associated card. This avoids executing the card mark
+ // if the CAS fails. However, it can be seen from the diagram below
+ // that the presence of the barrier does not alter the normal CAS
+ // memory subgraph where the leading membar feeds a CompareAndSwapX,
+ // an SCMemProj, a MergeMem then a final trailing MemBarCPUOrder and
+ // MemBarAcquire pair.
//
// MemBarRelease
- // MemBarCPUOrder__(leading)_________________________
- // || \\ C \
- // MemBarVolatile (card mark) CompareAndSwapN/P CastP2X
- // C | || M | |
- // | LoadB | ______/|
- // | | | / |
- // | Cmp | / SCMemProj
- // | / | / |
- // If | / /
- // | \ | / /
- // IfFalse IfTrue | / /
- // \ / \ |/ prec /
- // \ / StoreCM /
- // \ / | /
- // Region . . . /
- // | \ /
- // | . . . \ / Bot
- // | MergeMem
- // | |
- // MemBarCPUOrder
- // MemBarAcquire (trailing)
+ // MemBarCPUOrder__(leading)_______________________
+ // C / M | \\ C \
+ // . . . | Bot CompareAndSwapN/P CastP2X
+ // | C / M |
+ // | CmpI |
+ // | / |
+ // | . . . |
+ // | IfTrue |
+ // | / |
+ // MemBarVolatile (card mark) |
+ // C | || M | |
+ // | LoadB | Bot ______/|
+ // | | | / |
+ // | Cmp | / SCMemProj
+ // | / | / |
+ // If | / /
+ // | \ | / / Bot
+ // IfFalse IfTrue | / /
+ // | / \ / / prec /
+ // . . . | / StoreCM /
+ // \ | / | raw /
+ // Region . . . /
+ // | \ /
+ // | . . . \ / Bot
+ // | MergeMem
+ // | /
+ // MemBarCPUOrder
+ // MemBarAcquire (trailing)
//
// This has a slightly different memory subgraph to the one seen
- // previously but the core of it is the same as for the CAS normal
- // sungraph
+ // previously but the core of it has a similar memory flow to the
+ // CAS normal subgraph:
//
// MemBarRelease
// MemBarCPUOrder____
- // || \ . . .
- // MemBarVolatile CompareAndSwapX . . .
- // | \ |
- // . . . SCMemProj
- // | / . . .
- // MergeMem
- // |
+ // | \ . . .
+ // | CompareAndSwapX . . .
+ // | C / M |
+ // | CmpI |
+ // | / |
+ // | . . /
+ // Bot | IfTrue /
+ // | / /
+ // MemBarVolatile /
+ // | ... /
+ // StoreCM ... /
+ // | /
+ // . . . SCMemProj
+ // Raw \ / Bot
+ // MergeMem
+ // |
// MemBarCPUOrder
// MemBarAcquire
//
- //
- // G1 is quite a lot more complicated. The nodes inserted on behalf
- // of G1 may comprise: a pre-write graph which adds the old value to
- // the SATB queue; the releasing store itself; and, finally, a
- // post-write graph which performs a card mark.
+ // The G1 graph for a volatile object put is a lot more complicated.
+ // Nodes inserted on behalf of G1 may comprise: a pre-write graph
+ // which adds the old value to the SATB queue; the releasing store
+ // itself; and, finally, a post-write graph which performs a card
+ // mark.
//
// The pre-write graph may be omitted, but only when the put is
// writing to a newly allocated (young gen) object and then only if
@@ -1730,25 +1749,60 @@
// | CastP2X | StoreN/P[mo_release] |
// | | | |
// C | M | M | M |
- // \ | | /
+ // \ | Raw | oop / Bot
// . . .
// (post write subtree elided)
// . . .
// C \ M /
// MemBarVolatile (trailing)
//
+ // Note that the three memory feeds into the post-write tree are an
+ // AliasRawIdx slice associated with the writes in the pre-write
+ // tree, an oop type slice from the StoreX specific to the type of
+ // the volatile field and the AliasBotIdx slice emanating from the
+ // leading membar.
+ //
// n.b. the LoadB in this subgraph is not the card read -- it's a
// read of the SATB queue active flag.
//
- // Once again the CAS graph is a minor variant on the above with the
- // expected substitutions of CompareAndSawpX for StoreN/P and
- // MemBarCPUOrder + MemBarAcquire for trailing MemBarVolatile.
+ // The CAS graph is once again a variant of the above with a
+ // CompareAndSwapX node and SCMemProj in place of the StoreX. The
+ // value from the CompareAndSwapX node is fed into the post-write
+ // graph aling with the AliasIdxRaw feed from the pre-barrier and
+ // the AliasIdxBot feeds from the leading membar and the ScMemProj.
+ //
+ // MemBarRelease (leading)____________
+ // C | || M \ M \ M \ M \ . . .
+ // | LoadB \ LoadL LoadN \
+ // | / \ \
+ // If |\ \
+ // | \ | \ \
+ // IfFalse IfTrue | \ \
+ // | | | \ \
+ // | If | \ |
+ // | | \ |
+ // | \ |
+ // | . . . \ |
+ // | / | / \ |
+ // Region Phi[M] \ |
+ // | \ | \ |
+ // | \_____ | | |
+ // C | C \ | | |
+ // | CastP2X | CompareAndSwapX |
+ // | | res | | |
+ // C | M | | SCMemProj M |
+ // \ | Raw | | Bot / Bot
+ // . . .
+ // (post write subtree elided)
+ // . . .
+ // C \ M /
+ // MemBarVolatile (trailing)
//
// The G1 post-write subtree is also optional, this time when the
// new value being written is either null or can be identified as a
// newly allocated (young gen) object with no intervening control
// flow. The latter cannot happen but the former may, in which case
- // the card mark membar is omitted and the memory feeds form the
+ // the card mark membar is omitted and the memory feeds from the
// leading membar and the SToreN/P are merged direct into the
// trailing membar as per the normal subgraph. So, the only special
// case which arises is when the post-write subgraph is generated.
@@ -1770,94 +1824,106 @@
//
// (pre-write subtree elided)
// . . . . . . . . . . . .
- // C | M | M | M |
- // Region Phi[M] StoreN |
- // | / \ | |
- // / \_______ / \ | |
- // C / C \ . . . \ | |
- // If CastP2X . . . | | |
- // / \ | | |
- // / \ | | |
- // IfFalse IfTrue | | |
- // | | | | /|
- // | If | | / |
- // | / \ | | / |
- // | / \ \ | / |
- // | IfFalse IfTrue MergeMem |
- // | . . . / \ / |
- // | / \ / |
- // | IfFalse IfTrue / |
- // | . . . | / |
- // | If / |
- // | / \ / |
- // | / \ / |
- // | IfFalse IfTrue / |
- // | . . . | / |
- // | \ / |
- // | \ / |
- // | MemBarVolatile__(card mark) |
- // | || C | M \ M \ |
- // | LoadB If | | |
- // | / \ | | |
- // | . . . | | |
- // | \ | | /
- // | StoreCM | /
- // | . . . | /
- // | _________/ /
- // | / _____________/
- // | . . . . . . | / /
- // | | | / _________/
- // | | Phi[M] / /
- // | | | / /
- // | | | / /
- // | Region . . . Phi[M] _____/
- // | / | /
- // | | /
- // | . . . . . . | /
- // | / | /
- // Region | | Phi[M]
- // | | | / Bot
- // \ MergeMem
- // \ /
- // MemBarVolatile
- //
- // As with CMS the initial MergeMem merges the AliasIdxBot Mem slice
- // from the leading membar and the oopptr Mem slice from the Store
- // into the card mark membar i.e. the memory flow to the card mark
- // membar still looks like a normal graph.
- //
- // The trailing MergeMem merges an AliasIdxBot Mem slice with other
- // Mem slices (from the StoreCM and other card mark queue stores).
- // However in this case the AliasIdxBot Mem slice does not come
- // direct from the card mark membar. It is merged through a series
- // of Phi nodes. These are needed to merge the AliasIdxBot Mem flow
- // from the leading membar with the Mem feed from the card mark
- // membar. Each Phi corresponds to one of the Ifs which may skip
- // around the card mark membar. So when the If implementing the NULL
- // value check has been elided the total number of Phis is 2
- // otherwise it is 3.
- //
- // The CAS graph when using G1GC also includes a pre-write subgraph
- // and an optional post-write subgraph. Teh sam evarioations are
- // introduced as for CMS with conditional card marking i.e. the
- // StoreP/N is swapped for a CompareAndSwapP/N, the tariling
- // MemBarVolatile for a MemBarCPUOrder + MemBarAcquire pair and the
- // Mem feed from the CompareAndSwapP/N includes a precedence
- // dependency feed to the StoreCM and a feed via an SCMemProj to the
- // trailing membar. So, as before the configuration includes the
- // normal CAS graph as a subgraph of the memory flow.
- //
- // So, the upshot is that in all cases the volatile put graph will
- // include a *normal* memory subgraph betwen the leading membar and
- // its child membar, either a volatile put graph (including a
- // releasing StoreX) or a CAS graph (including a CompareAndSwapX).
- // When that child is not a card mark membar then it marks the end
- // of the volatile put or CAS subgraph. If the child is a card mark
- // membar then the normal subgraph will form part of a volatile put
- // subgraph if and only if the child feeds an AliasIdxBot Mem feed
- // to a trailing barrier via a MergeMem. That feed is either direct
- // (for CMS) or via 2 or 3 Phi nodes merging the leading barrier
- // memory flow (for G1).
+ // C | M | M | M |
+ // Region Phi[M] StoreN |
+ // | Raw | oop | Bot |
+ // / \_______ |\ |\ |\
+ // C / C \ . . . | \ | \ | \
+ // If CastP2X . . . | \ | \ | \
+ // / \ | \ | \ | \
+ // / \ | \ | \ | \
+ // IfFalse IfTrue | | | \
+ // | | \ | / |
+ // | If \ | \ / \ |
+ // | / \ \ | / \ |
+ // | / \ \ | / \ | |
+ // | IfFalse IfTrue MergeMem \ | |
+ // | . . . / \ | \ | |
+ // | / \ | | | |
+ // | IfFalse IfTrue | | | |
+ // | . . . | | | | |
+ // | If / | | |
+ // | / \ / | | |
+ // | / \ / | | |
+ // | IfFalse IfTrue / | | |
+ // | . . . | / | | |
+ // | \ / | | |
+ // | \ / | | |
+ // | MemBarVolatile__(card mark ) | | |
+ // | || C | \ | | |
+ // | LoadB If | / | |
+ // | / \ Raw | / / /
+ // | . . . | / / /
+ // | \ | / / /
+ // | StoreCM / / /
+ // | | / / /
+ // | . . . / /
+ // | / /
+ // | . . . / /
+ // | | | / / /
+ // | | Phi[M] / / /
+ // | | | / / /
+ // | | | / / /
+ // | Region . . . Phi[M] / /
+ // | | | / /
+ // \ | | / /
+ // \ | . . . | / /
+ // \ | | / /
+ // Region Phi[M] / /
+ // | \ / /
+ // \ MergeMem
+ // \ /
+ // MemBarVolatile
+ //
+ // As with CMS + CondCardMark the first MergeMem merges the
+ // AliasIdxBot Mem slice from the leading membar and the oopptr Mem
+ // slice from the Store into the card mark membar. However, in this
+ // case it may also merge an AliasRawIdx mem slice from the pre
+ // barrier write.
+ //
+ // The trailing MergeMem merges an AliasIdxBot Mem slice from the
+ // leading membar with an oop slice from the StoreN and an
+ // AliasRawIdx slice from the post barrier writes. In this case the
+ // AliasIdxRaw Mem slice is merged through a series of Phi nodes
+ // which combine feeds from the If regions in the post barrier
+ // subgraph.
+ //
+ // So, for G1 the same characteristic subgraph arises as for CMS +
+ // CondCardMark. There is a normal subgraph feeding the card mark
+ // membar and a normal subgraph feeding the trailing membar.
+ //
+ // The CAS graph when using G1GC also includes an optional
+ // post-write subgraph. It is very similar to the above graph except
+ // for a few details.
+ //
+ // - The control flow is gated by an additonal If which tests the
+ // result from the CompareAndSwapX node
+ //
+ // - The MergeMem which feeds the card mark membar only merges the
+ // AliasIdxBot slice from the leading membar and the AliasIdxRaw
+ // slice from the pre-barrier. It does not merge the SCMemProj
+ // AliasIdxBot slice. So, this subgraph does not look like the
+ // normal CAS subgraph.
+ //
+ // - The MergeMem which feeds the trailing membar merges the
+ // AliasIdxBot slice from the leading membar, the AliasIdxRaw slice
+ // from the post-barrier and the SCMemProj AliasIdxBot slice i.e. it
+ // has two AliasIdxBot input slices. However, this subgraph does
+ // still look like the normal CAS subgraph.
+ //
+ // So, the upshot is:
+ //
+ // In all cases a volatile put graph will include a *normal*
+ // volatile store subgraph betwen the leading membar and the
+ // trailing membar. It may also include a normal volatile store
+ // subgraph betwen the leading membar and the card mark membar.
+ //
+ // In all cases a CAS graph will contain a unique normal CAS graph
+ // feeding the trailing membar.
+ //
+ // In all cases where there is a card mark membar (either as part of
+ // a volatile object put or CAS) it will be fed by a MergeMem whose
+ // AliasIdxBot slice feed will be a leading membar.
//
// The predicates controlling generation of instructions for store
// and barrier nodes employ a few simple helper functions (described
@@ -1878,24 +1944,24 @@
opcode == Op_CompareAndSwapP);
}
- // leading_to_normal
+ // leading_to_trailing
//
//graph traversal helper which detects the normal case Mem feed from
// a release membar (or, optionally, its cpuorder child) to a
// dependent volatile membar i.e. it ensures that one or other of
// the following Mem flow subgraph is present.
//
- // MemBarRelease
- // MemBarCPUOrder {leading}
- // | \ . . .
- // | StoreN/P[mo_release] . . .
- // | /
- // MergeMem
- // |
- // MemBarVolatile {trailing or card mark}
- //
- // MemBarRelease
- // MemBarCPUOrder {leading}
+ // MemBarRelease {leading}
+ // {MemBarCPUOrder} {optional}
+ // Bot | \ . . .
+ // | StoreN/P[mo_release] . . .
+ // | /
+ // MergeMem
+ // |
+ // MemBarVolatile {not card mark}
+ //
+ // MemBarRelease {leading}
+ // {MemBarCPUOrder} {optional}
// | \ . . .
// | CompareAndSwapX . . .
// |
@@ -1906,6 +1972,23 @@
// MemBarCPUOrder
// MemBarAcquire {trailing}
//
+ // the predicate needs to be capable of distinguishing the following
+ // volatile put graph which may arises when a GC post barrier
+ // inserts a card mark membar
+ //
+ // MemBarRelease {leading}
+ // {MemBarCPUOrder}__
+ // Bot | \ \
+ // | StoreN/P \
+ // | / \ |
+ // MergeMem \ |
+ // | \ |
+ // MemBarVolatile \ |
+ // {card mark} \ |
+ // MergeMem
+ // |
+ // {not card mark} MemBarVolatile
+ //
// if the correct configuration is present returns the trailing
// membar otherwise NULL.
//
@@ -1916,7 +1999,7 @@
// the returned value may be a card mark or trailing membar
//
- MemBarNode *leading_to_normal(MemBarNode *leading)
+ MemBarNode *leading_to_trailing(MemBarNode *leading)
{
assert((leading->Opcode() == Op_MemBarRelease ||
leading->Opcode() == Op_MemBarCPUOrder),
@@ -1933,15 +2016,21 @@
StoreNode * st = NULL;
LoadStoreNode *cas = NULL;
MergeMemNode *mm = NULL;
+ MergeMemNode *mm2 = NULL;
for (DUIterator_Fast imax, i = mem->fast_outs(imax); i < imax; i++) {
x = mem->fast_out(i);
if (x->is_MergeMem()) {
if (mm != NULL) {
- return NULL;
+ if (mm2 != NULL) {
+ // should not see more than 2 merge mems
+ return NULL;
+ } else {
+ mm2 = x->as_MergeMem();
+ }
+ } else {
+ mm = x->as_MergeMem();
}
- // two merge mems is one too many
- mm = x->as_MergeMem();
} else if (x->is_Store() && x->as_Store()->is_release() && x->Opcode() != Op_StoreCM) {
// two releasing stores/CAS nodes is one too many
if (st != NULL || cas != NULL) {
@@ -1961,13 +2050,13 @@
return NULL;
}
- // must have a merge if we also have st
+ // must have at least one merge if we also have st
if (st && !mm) {
return NULL;
}
- Node *y = NULL;
if (cas) {
+ Node *y = NULL;
// look for an SCMemProj
for (DUIterator_Fast imax, i = cas->fast_outs(imax); i < imax; i++) {
x = cas->fast_out(i);
@@ -1987,10 +2076,29 @@
break;
}
}
- if (mm == NULL)
+ if (mm == NULL) {
return NULL;
+ }
+ MemBarNode *mbar = NULL;
+ // ensure the merge feeds a trailing membar cpuorder + acquire pair
+ for (DUIterator_Fast imax, i = mm->fast_outs(imax); i < imax; i++) {
+ x = mm->fast_out(i);
+ if (x->is_MemBar()) {
+ int opcode = x->Opcode();
+ if (opcode == Op_MemBarCPUOrder) {
+ MemBarNode *z = x->as_MemBar();
+ z = child_membar(z);
+ if (z != NULL && z->Opcode() == Op_MemBarAcquire) {
+ mbar = z;
+ }
+ }
+ break;
+ }
+ }
+ return mbar;
} else {
- // ensure the store feeds the existing mergemem;
+ Node *y = NULL;
+ // ensure the store feeds the first mergemem;
for (DUIterator_Fast imax, i = st->fast_outs(imax); i < imax; i++) {
if (st->fast_out(i) == mm) {
y = st;
@@ -2000,55 +2108,89 @@
if (y == NULL) {
return NULL;
}
- }
-
- MemBarNode *mbar = NULL;
- // ensure the merge feeds to the expected type of membar
- for (DUIterator_Fast imax, i = mm->fast_outs(imax); i < imax; i++) {
- x = mm->fast_out(i);
- if (x->is_MemBar()) {
- int opcode = x->Opcode();
- if (opcode == Op_MemBarVolatile && st) {
- mbar = x->as_MemBar();
- } else if (cas && opcode == Op_MemBarCPUOrder) {
- MemBarNode *y = x->as_MemBar();
- y = child_membar(y);
- if (y != NULL && y->Opcode() == Op_MemBarAcquire) {
- mbar = y;
+ if (mm2 != NULL) {
+ // ensure the store feeds the second mergemem;
+ y = NULL;
+ for (DUIterator_Fast imax, i = st->fast_outs(imax); i < imax; i++) {
+ if (st->fast_out(i) == mm2) {
+ y = st;
}
}
- break;
+ if (y == NULL) {
+ return NULL;
+ }
+ }
+
+ MemBarNode *mbar = NULL;
+ // ensure the first mergemem feeds a volatile membar
+ for (DUIterator_Fast imax, i = mm->fast_outs(imax); i < imax; i++) {
+ x = mm->fast_out(i);
+ if (x->is_MemBar()) {
+ int opcode = x->Opcode();
+ if (opcode == Op_MemBarVolatile) {
+ mbar = x->as_MemBar();
+ }
+ break;
+ }
+ }
+ if (mm2 == NULL) {
+ // this is our only option for a trailing membar
+ return mbar;
}
- }
-
- return mbar;
- }
-
- // normal_to_leading
+ // ensure the second mergemem feeds a volatile membar
+ MemBarNode *mbar2 = NULL;
+ for (DUIterator_Fast imax, i = mm2->fast_outs(imax); i < imax; i++) {
+ x = mm2->fast_out(i);
+ if (x->is_MemBar()) {
+ int opcode = x->Opcode();
+ if (opcode == Op_MemBarVolatile) {
+ mbar2 = x->as_MemBar();
+ }
+ break;
+ }
+ }
+ // if we have two merge mems we must have two volatile membars
+ if (mbar == NULL || mbar2 == NULL) {
+ return NULL;
+ }
+ // return the trailing membar
+ if (is_card_mark_membar(mbar2)) {
+ return mbar;
+ } else {
+ if (is_card_mark_membar(mbar)) {
+ return mbar2;
+ } else {
+ return NULL;
+ }
+ }
+ }
+ }
+
+ // trailing_to_leading
//
// graph traversal helper which detects the normal case Mem feed
- // from either a card mark or a trailing membar to a preceding
- // release membar (optionally its cpuorder child) i.e. it ensures
- // that one or other of the following Mem flow subgraphs is present.
- //
- // MemBarRelease
- // MemBarCPUOrder {leading}
- // | \ . . .
- // | StoreN/P[mo_release] . . .
- // | /
- // MergeMem
- // |
- // MemBarVolatile {card mark or trailing}
- //
- // MemBarRelease
- // MemBarCPUOrder {leading}
+ // from a trailing membar to a preceding release membar (optionally
+ // its cpuorder child) i.e. it ensures that one or other of the
+ // following Mem flow subgraphs is present.
+ //
+ // MemBarRelease {leading}
+ // MemBarCPUOrder {optional}
+ // | Bot | \ . . .
+ // | | StoreN/P[mo_release] . . .
+ // | | /
+ // | MergeMem
+ // | |
+ // MemBarVolatile {not card mark}
+ //
+ // MemBarRelease {leading}
+ // MemBarCPUOrder {optional}
// | \ . . .
// | CompareAndSwapX . . .
// |
// . . . SCMemProj
// \ |
// | MergeMem
- // | /
+ // | |
// MemBarCPUOrder
// MemBarAcquire {trailing}
//
@@ -2058,15 +2200,20 @@
// if the configuration is present returns the cpuorder member for
// preference or when absent the release membar otherwise NULL.
//
- // n.b. the input membar is expected to be a MemBarVolatile but
- // need not be a card mark membar.
-
- MemBarNode *normal_to_leading(const MemBarNode *barrier)
+ // n.b. the input membar is expected to be a MemBarVolatile or
+ // MemBarAcquire. if it is a MemBarVolatile it must *not* be a card
+ // mark membar.
+
+ MemBarNode *trailing_to_leading(const MemBarNode *barrier)
{
// input must be a volatile membar
assert((barrier->Opcode() == Op_MemBarVolatile ||
barrier->Opcode() == Op_MemBarAcquire),
"expecting a volatile or an acquire membar");
+
+ assert((barrier->Opcode() != Op_MemBarVolatile) ||
+ !is_card_mark_membar(barrier),
+ "not expecting a card mark membar");
Node *x;
bool is_cas = barrier->Opcode() == Op_MemBarAcquire;
@@ -2179,169 +2326,35 @@
return NULL;
}
- // card_mark_to_trailing
- //
- // graph traversal helper which detects extra, non-normal Mem feed
- // from a card mark volatile membar to a trailing membar i.e. it
- // ensures that one of the following three GC post-write Mem flow
- // subgraphs is present.
- //
- // 1)
- // . . .
- // |
- // MemBarVolatile (card mark)
- // | |
- // | StoreCM
- // | |
- // | . . .
- // Bot | /
- // MergeMem
- // |
- // |
- // MemBarVolatile {trailing}
- //
- // 2)
- // MemBarRelease/CPUOrder (leading)
- // |
- // |
- // |\ . . .
- // | \ |
- // | \ MemBarVolatile (card mark)
- // | \ | |
- // \ \ | StoreCM . . .
- // \ \ |
- // \ Phi
- // \ /
- // Phi . . .
+ // card_mark_to_leading
+ //
+ // graph traversal helper which traverses from a card mark volatile
+ // membar to a leading membar i.e. it ensures that the following Mem
+ // flow subgraph is present.
+ //
+ // MemBarRelease {leading}
+ // {MemBarCPUOrder} {optional}
+ // | . . .
// Bot | /
- // MergeMem
+ // MergeMem
// |
- // MemBarVolatile {trailing}
- //
- //
- // 3)
- // MemBarRelease/CPUOrder (leading)
- // |
- // |\
- // | \
- // | \ . . .
- // | \ |
- // |\ \ MemBarVolatile (card mark)
- // | \ \ | |
- // | \ \ | StoreCM . . .
- // | \ \ |
- // \ \ Phi
- // \ \ /
- // \ Phi
- // \ /
- // Phi . . .
- // Bot | /
- // MergeMem
- // |
- // |
- // MemBarVolatile {trailing}
- //
- // configuration 1 is only valid if UseConcMarkSweepGC &&
- // UseCondCardMark
- //
- // configurations 2 and 3 are only valid if UseG1GC.
- //
- // if a valid configuration is present returns the trailing membar
- // otherwise NULL.
- //
- // n.b. the supplied membar is expected to be a card mark
- // MemBarVolatile i.e. the caller must ensure the input node has the
- // correct operand and feeds Mem to a StoreCM node
-
- MemBarNode *card_mark_to_trailing(const MemBarNode *barrier)
+ // MemBarVolatile (card mark)
+ // | \
+ // . . . StoreCM
+ //
+ // if the configuration is present returns the cpuorder member for
+ // preference or when absent the release membar otherwise NULL.
+ //
+ // n.b. the input membar is expected to be a MemBarVolatile amd must
+ // be a card mark membar.
+
+ MemBarNode *card_mark_to_leading(const MemBarNode *barrier)
{
// input must be a card mark volatile membar
assert(is_card_mark_membar(barrier), "expecting a card mark membar");
- Node *feed = barrier->proj_out(TypeFunc::Memory);
- Node *x;
- MergeMemNode *mm = NULL;
-
- const int MAX_PHIS = 3; // max phis we will search through
- int phicount = 0; // current search count
-
- bool retry_feed = true;
- while (retry_feed) {
- // see if we have a direct MergeMem feed
- for (DUIterator_Fast imax, i = feed->fast_outs(imax); i < imax; i++) {
- x = feed->fast_out(i);
- // the correct Phi will be merging a Bot memory slice
- if (x->is_MergeMem()) {
- mm = x->as_MergeMem();
- break;
- }
- }
- if (mm) {
- retry_feed = false;
- } else if (UseG1GC & phicount++ < MAX_PHIS) {
- // the barrier may feed indirectly via one or two Phi nodes
- PhiNode *phi = NULL;
- for (DUIterator_Fast imax, i = feed->fast_outs(imax); i < imax; i++) {
- x = feed->fast_out(i);
- // the correct Phi will be merging a Bot memory slice
- if (x->is_Phi() && x->adr_type() == TypePtr::BOTTOM) {
- phi = x->as_Phi();
- break;
- }
- }
- if (!phi) {
- return NULL;
- }
- // look for another merge below this phi
- feed = phi;
- } else {
- // couldn't find a merge
- return NULL;
- }
- }
-
- // sanity check this feed turns up as the expected slice
- assert(mm->as_MergeMem()->in(Compile::AliasIdxBot) == feed, "expecting membar to feed AliasIdxBot slice to Merge");
-
- MemBarNode *trailing = NULL;
- // be sure we have a trailing membar the merge
- for (DUIterator_Fast imax, i = mm->fast_outs(imax); i < imax; i++) {
- x = mm->fast_out(i);
- if (x->is_MemBar() && x->Opcode() == Op_MemBarVolatile) {
- trailing = x->as_MemBar();
- break;
- }
- }
-
- return trailing;
- }
-
- // trailing_to_card_mark
- //
- // graph traversal helper which detects extra, non-normal Mem feed
- // from a trailing volatile membar to a preceding card mark volatile
- // membar i.e. it identifies whether one of the three possible extra
- // GC post-write Mem flow subgraphs is present
- //
- // this predicate checks for the same flow as the previous predicate
- // but starting from the bottom rather than the top.
- //
- // if the configuration is present returns the card mark membar
- // otherwise NULL
- //
- // n.b. the supplied membar is expected to be a trailing
- // MemBarVolatile i.e. the caller must ensure the input node has the
- // correct opcode
-
- MemBarNode *trailing_to_card_mark(const MemBarNode *trailing)
- {
- assert(trailing->Opcode() == Op_MemBarVolatile,
- "expecting a volatile membar");
- assert(!is_card_mark_membar(trailing),
- "not expecting a card mark membar");
-
// the Mem feed to the membar should be a merge
- Node *x = trailing->in(TypeFunc::Memory);
+ Node *x = barrier->in(TypeFunc::Memory);
if (!x->is_MergeMem()) {
return NULL;
}
@@ -2349,117 +2362,19 @@
MergeMemNode *mm = x->as_MergeMem();
x = mm->in(Compile::AliasIdxBot);
- // with G1 we may possibly see a Phi or two before we see a Memory
- // Proj from the card mark membar
-
- const int MAX_PHIS = 3; // max phis we will search through
- int phicount = 0; // current search count
-
- bool retry_feed = !x->is_Proj();
-
- while (retry_feed) {
- if (UseG1GC && x->is_Phi() && phicount++ < MAX_PHIS) {
- PhiNode *phi = x->as_Phi();
- ProjNode *proj = NULL;
- PhiNode *nextphi = NULL;
- bool found_leading = false;
- for (uint i = 1; i < phi->req(); i++) {
- x = phi->in(i);
- if (x->is_Phi()) {
- nextphi = x->as_Phi();
- } else if (x->is_Proj()) {
- int opcode = x->in(0)->Opcode();
- if (opcode == Op_MemBarVolatile) {
- proj = x->as_Proj();
- } else if (opcode == Op_MemBarRelease ||
- opcode == Op_MemBarCPUOrder) {
- // probably a leading membar
- found_leading = true;
- }
- }
- }
- // if we found a correct looking proj then retry from there
- // otherwise we must see a leading and a phi or this the
- // wrong config
- if (proj != NULL) {
- x = proj;
- retry_feed = false;
- } else if (found_leading && nextphi != NULL) {
- // retry from this phi to check phi2
- x = nextphi;
- } else {
- // not what we were looking for
- return NULL;
- }
- } else {
- return NULL;
- }
- }
- // the proj has to come from the card mark membar
- x = x->in(0);
+
if (!x->is_MemBar()) {
return NULL;
}
- MemBarNode *card_mark_membar = x->as_MemBar();
-
- if (!is_card_mark_membar(card_mark_membar)) {
- return NULL;
- }
-
- return card_mark_membar;
- }
-
- // trailing_to_leading
- //
- // graph traversal helper which checks the Mem flow up the graph
- // from a (non-card mark) trailing membar attempting to locate and
- // return an associated leading membar. it first looks for a
- // subgraph in the normal configuration (relying on helper
- // normal_to_leading). failing that it then looks for one of the
- // possible post-write card mark subgraphs linking the trailing node
- // to a the card mark membar (relying on helper
- // trailing_to_card_mark), and then checks that the card mark membar
- // is fed by a leading membar (once again relying on auxiliary
- // predicate normal_to_leading).
- //
- // if the configuration is valid returns the cpuorder member for
- // preference or when absent the release membar otherwise NULL.
- //
- // n.b. the input membar is expected to be either a volatile or
- // acquire membar but in the former case must *not* be a card mark
- // membar.
-
- MemBarNode *trailing_to_leading(const MemBarNode *trailing)
- {
- assert((trailing->Opcode() == Op_MemBarAcquire ||
- trailing->Opcode() == Op_MemBarVolatile),
- "expecting an acquire or volatile membar");
- assert((trailing->Opcode() != Op_MemBarVolatile ||
- !is_card_mark_membar(trailing)),
- "not expecting a card mark membar");
-
- MemBarNode *leading = normal_to_leading(trailing);
-
- if (leading) {
+ MemBarNode *leading = x->as_MemBar();
+
+ if (leading_membar(leading)) {
return leading;
}
- // nothing more to do if this is an acquire
- if (trailing->Opcode() == Op_MemBarAcquire) {
- return NULL;
- }
-
- MemBarNode *card_mark_membar = trailing_to_card_mark(trailing);
-
- if (!card_mark_membar) {
- return NULL;
- }
-
- return normal_to_leading(card_mark_membar);
- }
-
- // predicates controlling emit of ldr<x>/ldar<x> and associated dmb
+ return NULL;
+ }
bool unnecessary_acquire(const Node *barrier)
{
@@ -2675,19 +2590,8 @@
}
// must start with a normal feed
- MemBarNode *child_barrier = leading_to_normal(barrier);
-
- if (!child_barrier) {
- return false;
- }
-
- if (!is_card_mark_membar(child_barrier)) {
- // this is the trailing membar and we are done
- return true;
- }
-
- // must be sure this card mark feeds a trailing membar
- MemBarNode *trailing = card_mark_to_trailing(child_barrier);
+ MemBarNode *trailing = leading_to_trailing(barrier);
+
return (trailing != NULL);
}
@@ -2709,7 +2613,7 @@
}
// ok, if it's not a card mark then we still need to check if it is
- // a trailing membar of a volatile put hgraph.
+ // a trailing membar of a volatile put graph.
return (trailing_to_leading(mbvol) != NULL);
}
@@ -2759,20 +2663,9 @@
}
// does this lead a normal subgraph?
- MemBarNode *mbvol = leading_to_normal(barrier);
-
- if (!mbvol) {
- return false;
- }
-
- // all done unless this is a card mark
- if (!is_card_mark_membar(mbvol)) {
- return true;
- }
-
- // we found a card mark -- just make sure we have a trailing barrier
-
- return (card_mark_to_trailing(mbvol) != NULL);
+ MemBarNode *trailing = leading_to_trailing(barrier);
+
+ return (trailing != NULL);
}
// predicate controlling translation of CAS
@@ -2814,7 +2707,7 @@
"CAS not fed by cpuorder+release membar pair!");
// does this lead a normal subgraph?
- MemBarNode *mbar = leading_to_normal(barrier);
+ MemBarNode *mbar = leading_to_trailing(barrier);
assert(mbar != NULL, "CAS not embedded in normal graph!");
@@ -2835,48 +2728,27 @@
// we only ever need to generate a dmb ishst between an object put
// and the associated card mark when we are using CMS without
- // conditional card marking
+ // conditional card marking. Any other occurence will happen when
+ // performing a card mark using CMS with conditional card marking or
+ // G1. In those cases the preceding MamBarVolatile will be
+ // translated to a dmb ish which guarantes visibility of the
+ // preceding StoreN/P before this StoreCM
if (!UseConcMarkSweepGC || UseCondCardMark) {
return true;
}
- // if we are implementing volatile puts using barriers then the
- // object put as an str so we must insert the dmb ishst
+ // if we are implementing volatile puts using barriers then we must
+ // insert the dmb ishst
if (UseBarriersForVolatile) {
return false;
}
- // we can omit the dmb ishst if this StoreCM is part of a volatile
- // put because in thta case the put will be implemented by stlr
- //
- // we need to check for a normal subgraph feeding this StoreCM.
- // that means the StoreCM must be fed Memory from a leading membar,
- // either a MemBarRelease or its dependent MemBarCPUOrder, and the
- // leading membar must be part of a normal subgraph
-
- Node *x = storecm->in(StoreNode::Memory);
-
- if (!x->is_Proj()) {
- return false;
- }
-
- x = x->in(0);
-
- if (!x->is_MemBar()) {
- return false;
- }
-
- MemBarNode *leading = x->as_MemBar();
-
- // reject invalid candidates
- if (!leading_membar(leading)) {
- return false;
- }
-
- // we can omit the StoreStore if it is the head of a normal subgraph
- return (leading_to_normal(leading) != NULL);
+ // we must be using CMS with conditional card marking so we ahve to
+ // generate the StoreStore
+
+ return false;
}