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8031818: Experimental VM flag for enforcing safe object construction
-XX:+AlwaysSafeConstructors to unconditionally emit the trailing constructor barrier. Reviewed-by: kvn, roland
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parent
c4bd0f58d3
commit
1d10b6813e
7 changed files with 74 additions and 22 deletions
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@ -391,6 +391,8 @@ Parse::Parse(JVMState* caller, ciMethod* parse_method, float expected_uses, Pars
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_depth = 1 + (caller->has_method() ? caller->depth() : 0);
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_wrote_final = false;
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_wrote_volatile = false;
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_wrote_stable = false;
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_wrote_fields = false;
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_alloc_with_final = NULL;
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_entry_bci = InvocationEntryBci;
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_tf = NULL;
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@ -908,26 +910,35 @@ void Parse::do_exits() {
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Node* iophi = _exits.i_o();
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_exits.set_i_o(gvn().transform(iophi));
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// On PPC64, also add MemBarRelease for constructors which write
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// volatile fields. As support_IRIW_for_not_multiple_copy_atomic_cpu
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// is set on PPC64, no sync instruction is issued after volatile
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// stores. We want to quarantee the same behaviour as on platforms
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// with total store order, although this is not required by the Java
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// memory model. So as with finals, we add a barrier here.
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if (wrote_final() PPC64_ONLY(|| (wrote_volatile() && method()->is_initializer()))) {
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// This method (which must be a constructor by the rules of Java)
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// wrote a final. The effects of all initializations must be
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// committed to memory before any code after the constructor
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// publishes the reference to the newly constructor object.
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// Rather than wait for the publication, we simply block the
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// writes here. Rather than put a barrier on only those writes
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// which are required to complete, we force all writes to complete.
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//
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// "All bets are off" unless the first publication occurs after a
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// normal return from the constructor. We do not attempt to detect
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// such unusual early publications. But no barrier is needed on
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// exceptional returns, since they cannot publish normally.
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//
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// Figure out if we need to emit the trailing barrier. The barrier is only
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// needed in the constructors, and only in three cases:
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//
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// 1. The constructor wrote a final. The effects of all initializations
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// must be committed to memory before any code after the constructor
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// publishes the reference to the newly constructed object. Rather
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// than wait for the publication, we simply block the writes here.
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// Rather than put a barrier on only those writes which are required
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// to complete, we force all writes to complete.
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//
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// 2. On PPC64, also add MemBarRelease for constructors which write
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// volatile fields. As support_IRIW_for_not_multiple_copy_atomic_cpu
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// is set on PPC64, no sync instruction is issued after volatile
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// stores. We want to guarantee the same behavior as on platforms
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// with total store order, although this is not required by the Java
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// memory model. So as with finals, we add a barrier here.
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//
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// 3. Experimental VM option is used to force the barrier if any field
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// was written out in the constructor.
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//
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// "All bets are off" unless the first publication occurs after a
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// normal return from the constructor. We do not attempt to detect
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// such unusual early publications. But no barrier is needed on
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// exceptional returns, since they cannot publish normally.
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//
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if (method()->is_initializer() &&
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(wrote_final() ||
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PPC64_ONLY(wrote_volatile() ||)
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(AlwaysSafeConstructors && wrote_fields()))) {
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_exits.insert_mem_bar(Op_MemBarRelease, alloc_with_final());
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#ifndef PRODUCT
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if (PrintOpto && (Verbose || WizardMode)) {
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@ -937,6 +948,19 @@ void Parse::do_exits() {
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#endif
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}
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// Any method can write a @Stable field; insert memory barriers after
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// those also. If there is a predecessor allocation node, bind the
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// barrier there.
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if (wrote_stable()) {
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_exits.insert_mem_bar(Op_MemBarRelease, alloc_with_final());
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#ifndef PRODUCT
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if (PrintOpto && (Verbose || WizardMode)) {
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method()->print_name();
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tty->print_cr(" writes @Stable and needs a memory barrier");
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}
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#endif
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}
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for (MergeMemStream mms(_exits.merged_memory()); mms.next_non_empty(); ) {
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// transform each slice of the original memphi:
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mms.set_memory(_gvn.transform(mms.memory()));
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