[RFR] Remove MemBarRelease when final field's allocation is NoEscape or ArgEscape

[Hui Shi]

Thanks Vladimir!

New patch keeps original "alloc->as_Allocate()->_is_non_escaping" check
with InitializeNode->does_not_escape() check.
Another similar place is PhaseMacroExpand::expand_allocate_common, where
generate MemBarStoreStore for allocation node. If AllocateNode is not
escape, it doesn't need generate MemBarStoreStore no matter its
InitializeNode NULL or not.

diff -r 720d0ff40323 src/share/vm/opto/macro.cpp
--- a/src/share/vm/opto/macro.cpp Mon Sep 14 07:03:04 2015 +0000
+++ b/src/share/vm/opto/macro.cpp Mon Sep 14 19:33:46 2015 +0800
@@ -1512,7 +1512,8 @@
     // MemBarStoreStore so that stores that initialize this object
     // can't be reordered with a subsequent store that makes this
     // object accessible by other threads.
-    if (init == NULL || (!init->is_complete_with_arraycopy() &&
!init->does_not_escape())) {
+    if (!alloc->_is_non_escaping &&
+        (init == NULL || (!init->is_complete_with_arraycopy() &&
!init->does_not_escape()))) {
       if (init == NULL || init->req() < InitializeNode::RawStores) {
         // No InitializeNode or no stores captured by zeroing
         // elimination. Simply add the MemBarStoreStore after object
diff -r 720d0ff40323 src/share/vm/opto/memnode.cpp
--- a/src/share/vm/opto/memnode.cpp Mon Sep 14 07:03:04 2015 +0000
+++ b/src/share/vm/opto/memnode.cpp Mon Sep 14 19:33:46 2015 +0800
@@ -2944,8 +2944,11 @@
     } else if (opc == Op_MemBarRelease) {
       // Final field stores.
       Node* alloc =
AllocateNode::Ideal_allocation(in(MemBarNode::Precedent), phase);
+      InitializeNode* init = NULL;
       if ((alloc != NULL) && alloc->is_Allocate() &&
-          alloc->as_Allocate()->_is_non_escaping) {
+          (alloc->as_Allocate()->_is_non_escaping ||
+           ((init = alloc->as_Allocate()->initialization()) != NULL &&
+            init->does_not_escape()))) {
         // The allocated object does not escape.
         eliminate = true;
       }


Regards
Shi Hui

On 14 September 2015 at 01:37, Vladimir Kozlov <vladimir.kozlov at oracle.com>
wrote:

> Please keep original AllocateNode check and add new check with ||.
> There are cases when there is no InitializeNode associated with allocation
> (when there are no access to object) so we need to keep first check.
>
> Thanks,
> Vladimir
>
> On 9/8/15 5:41 AM, Hui Shi wrote:
>
>> Hi JIT members,
>>
>>
>> There might be better use of escape analysis result when optimizing
>> MemBarRelease node for final field stores. Could anyone help review and
>> comments?
>>
>> Patch in
>> http://people.linaro.org/~hui.shi/MemBarRelease_Escape/MemBarEscape.patch
>>
>> __
>>
>> In hotspot, there are two different escape information recorded on a node.
>>
>> 1. AlllocateNode._is_non_escaping, true means allocation node’s escape
>> state is noEscape.____
>>
>> 2. InitializeNode._does_not_escape, true means its allocation node’s
>> escape state is noEscape or ArgEscape.____
>>
>> NoEscape has literal meaning. ArgEscape means allocation node is passed
>> to callee but will not escape current thread. So ArgEscape is safe to
>> remove MemBarRelase node for final field store in initialization
>> method.____
>>
>> __ __
>>
>> Pasted test creates an Integer instance in foo, MemBarRelase node is
>> created at the end of initialization method as Integer's value field is
>> final. New instance is ArgEscaped because it is passed to bar (disable
>> inlining bar). It fails to remove MemBarRelase node now, because
>> AlllocateNode._is_non_escaping is used in MemBarNode::Ideal(PhaseGVN
>> *phase, bool can_reshape) and this flag is false.____
>>
>> __ __
>>
>> public class TestInteger {____
>>
>>    public static void main(String[] args) {____
>>
>>       for(int i = 0; i < 1000000; i ++)____
>>
>>         foo(i);____
>>
>>    }____
>>
>> __ __
>>
>>    static int foo(int i) {____
>>
>>      Integer newi = new Integer(i);____
>>
>>      return bar(newi);____
>>
>>    }____
>>
>> __ __
>>
>>    static int bar(Integer i) {____
>>
>>      return i.intValue() + 2;____
>>
>>    }____
>>
>> }____
>>
>> __ __
>>
>> This patch deletes MemBarRelease node when its allocation node is
>> ArgEscape or NoEscape by checking its InitializeNode._does_not_escape
>> flag.____
>>
>>
>> Regards
>>
>> Shi Hui
>>
>>
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