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8296170: Refactor stack-locking path in C2_MacroAssembler::fast_unlock() #10936

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8296170: Refactor stack-locking path in C2_MacroAssembler::fast_unlock() #10936

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40817c8
8296170: Refactor stack-locking path in C2_MacroAssembler::fast_unlock()
rkennke Nov 1, 2022
bc4fd91
Merge remote-tracking branch 'upstream/master' into JDK-8296170
Nov 10, 2022
153353a
Remove comments about DONE_LABEL being a hot target
Nov 11, 2022
a75c36b
Merge branch 'master' into JDK-8296170
rkennke Nov 16, 2022
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34 changes: 5 additions & 29 deletions src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp
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Expand Up @@ -704,11 +704,6 @@ void C2_MacroAssembler::fast_lock(Register objReg, Register boxReg, Register tmp
#if INCLUDE_RTM_OPT
} // use_rtm()
#endif
// DONE_LABEL is a hot target - we'd really like to place it at the
// start of cache line by padding with NOPs.
// See the AMD and Intel software optimization manuals for the
// most efficient "long" NOP encodings.
// Unfortunately none of our alignment mechanisms suffice.
bind(DONE_LABEL);

// ZFlag == 1 count in fast path
Expand Down Expand Up @@ -770,7 +765,7 @@ void C2_MacroAssembler::fast_unlock(Register objReg, Register boxReg, Register t
assert(boxReg == rax, "");
assert_different_registers(objReg, boxReg, tmpReg);

Label DONE_LABEL, Stacked, CheckSucc, COUNT, NO_COUNT;
Label DONE_LABEL, Stacked, COUNT, NO_COUNT;

#if INCLUDE_RTM_OPT
if (UseRTMForStackLocks && use_rtm) {
Expand Down Expand Up @@ -829,8 +824,6 @@ void C2_MacroAssembler::fast_unlock(Register objReg, Register boxReg, Register t
// each other and there's no need for an explicit barrier (fence).
// See also http://gee.cs.oswego.edu/dl/jmm/cookbook.html.
#ifndef _LP64
get_thread (boxReg);

// Note that we could employ various encoding schemes to reduce
// the number of loads below (currently 4) to just 2 or 3.
// Refer to the comments in synchronizer.cpp.
Expand All @@ -840,30 +833,12 @@ void C2_MacroAssembler::fast_unlock(Register objReg, Register boxReg, Register t
jccb (Assembler::notZero, DONE_LABEL);
movptr(boxReg, Address(tmpReg, OM_OFFSET_NO_MONITOR_VALUE_TAG(EntryList)));
orptr(boxReg, Address(tmpReg, OM_OFFSET_NO_MONITOR_VALUE_TAG(cxq)));
jccb (Assembler::notZero, CheckSucc);
jccb (Assembler::notZero, DONE_LABEL);
movptr(Address(tmpReg, OM_OFFSET_NO_MONITOR_VALUE_TAG(owner)), NULL_WORD);
jmpb (DONE_LABEL);

bind (Stacked);
// It's not inflated and it's not recursively stack-locked.
// It must be stack-locked.
// Try to reset the header to displaced header.
// The "box" value on the stack is stable, so we can reload
// and be assured we observe the same value as above.
movptr(tmpReg, Address(boxReg, 0));
lock();
cmpxchgptr(tmpReg, Address(objReg, oopDesc::mark_offset_in_bytes())); // Uses RAX which is box
// Intention fall-thru into DONE_LABEL

// DONE_LABEL is a hot target - we'd really like to place it at the
// start of cache line by padding with NOPs.
// See the AMD and Intel software optimization manuals for the
// most efficient "long" NOP encodings.
// Unfortunately none of our alignment mechanisms suffice.
bind (CheckSucc);
#else // _LP64
// It's inflated
Label LNotRecursive, LSuccess, LGoSlowPath;
Label CheckSucc, LNotRecursive, LSuccess, LGoSlowPath;

cmpptr(Address(tmpReg, OM_OFFSET_NO_MONITOR_VALUE_TAG(recursions)), 0);
jccb(Assembler::equal, LNotRecursive);
Expand Down Expand Up @@ -936,13 +911,14 @@ void C2_MacroAssembler::fast_unlock(Register objReg, Register boxReg, Register t
testl (boxReg, 0); // set ICC.ZF=1 to indicate success
jmpb (DONE_LABEL);

#endif
if (!UseHeavyMonitors) {
bind (Stacked);
movptr(tmpReg, Address (boxReg, 0)); // re-fetch
lock();
cmpxchgptr(tmpReg, Address(objReg, oopDesc::mark_offset_in_bytes())); // Uses RAX which is box
// Intentional fall-thru into DONE_LABEL
}
#endif
bind(DONE_LABEL);

// ZFlag == 1 count in fast path
Expand Down