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8031818: Experimental VM flag for enforcing safe object construction

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-XX:+AlwaysSafeConstructors to unconditionally emit the trailing constructor barrier.

Reviewed-by: kvn, roland
This commit is contained in:
Aleksey Shipilev 2014-03-03 15:31:27 +04:00
parent c4bd0f58d3
commit 1d10b6813e
7 changed files with 74 additions and 22 deletions
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64
hotspot/src/share/vm/opto/parse1.cpp
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@ -391,6 +391,8 @@ Parse::Parse(JVMState* caller, ciMethod* parse_method, float expected_uses, Pars
_depth = 1 + (caller->has_method() ? caller->depth() : 0);
_wrote_final = false;
_wrote_volatile = false;
_wrote_stable = false;
_wrote_fields = false;
_alloc_with_final = NULL;
_entry_bci = InvocationEntryBci;
_tf = NULL;
@ -908,26 +910,35 @@ void Parse::do_exits() {
Node* iophi = _exits.i_o();
_exits.set_i_o(gvn().transform(iophi));
// On PPC64, also add MemBarRelease for constructors which write
// volatile fields. As support_IRIW_for_not_multiple_copy_atomic_cpu
// is set on PPC64, no sync instruction is issued after volatile
// stores. We want to quarantee the same behaviour as on platforms
// with total store order, although this is not required by the Java
// memory model. So as with finals, we add a barrier here.
if (wrote_final() PPC64_ONLY(|| (wrote_volatile() && method()->is_initializer()))) {
// This method (which must be a constructor by the rules of Java)
// wrote a final. The effects of all initializations must be
// committed to memory before any code after the constructor
// publishes the reference to the newly constructor object.
// Rather than wait for the publication, we simply block the
// writes here. Rather than put a barrier on only those writes
// which are required to complete, we force all writes to complete.
//
// "All bets are off" unless the first publication occurs after a
// normal return from the constructor. We do not attempt to detect
// such unusual early publications. But no barrier is needed on
// exceptional returns, since they cannot publish normally.
//
// Figure out if we need to emit the trailing barrier. The barrier is only
// needed in the constructors, and only in three cases:
//
// 1. The constructor wrote a final. The effects of all initializations
// must be committed to memory before any code after the constructor
// publishes the reference to the newly constructed object. Rather
// than wait for the publication, we simply block the writes here.
// Rather than put a barrier on only those writes which are required
// to complete, we force all writes to complete.
//
// 2. On PPC64, also add MemBarRelease for constructors which write
// volatile fields. As support_IRIW_for_not_multiple_copy_atomic_cpu
// is set on PPC64, no sync instruction is issued after volatile
// stores. We want to guarantee the same behavior as on platforms
// with total store order, although this is not required by the Java
// memory model. So as with finals, we add a barrier here.
//
// 3. Experimental VM option is used to force the barrier if any field
// was written out in the constructor.
//
// "All bets are off" unless the first publication occurs after a
// normal return from the constructor. We do not attempt to detect
// such unusual early publications. But no barrier is needed on
// exceptional returns, since they cannot publish normally.
//
if (method()->is_initializer() &&
(wrote_final() ||
PPC64_ONLY(wrote_volatile() ||)
(AlwaysSafeConstructors && wrote_fields()))) {
_exits.insert_mem_bar(Op_MemBarRelease, alloc_with_final());
#ifndef PRODUCT
if (PrintOpto && (Verbose || WizardMode)) {
@ -937,6 +948,19 @@ void Parse::do_exits() {
#endif
}
// Any method can write a @Stable field; insert memory barriers after
// those also. If there is a predecessor allocation node, bind the
// barrier there.
if (wrote_stable()) {
_exits.insert_mem_bar(Op_MemBarRelease, alloc_with_final());
#ifndef PRODUCT
if (PrintOpto && (Verbose || WizardMode)) {
method()->print_name();
tty->print_cr(" writes @Stable and needs a memory barrier");
}
#endif
}
for (MergeMemStream mms(_exits.merged_memory()); mms.next_non_empty(); ) {
// transform each slice of the original memphi:
mms.set_memory(_gvn.transform(mms.memory()));