RFR: 8274983: C1 optimizes the invocation of private interface methods [v2]

[Dean Long]

On Wed, 24 Nov 2021 07:48:37 GMT, Xin Liu <xliu at openjdk.org> wrote:

>> The root cause of the C1 regression is that some regex generate multiple classes which all implement
>> an interface. In SlowStartupTest.java, the following **invokeinterface** happens frequently with different receivers. the target is a private interface method. 
>> 
>> 
>> 9: invokeinterface #25,  3           // InterfaceMethod java/util/regex/Pattern$BmpCharPredicate.lambda$union$2:(Ljava/util/regex/Pattern$CharPredicate;I)Z
>> 
>> 
>> This patch allows c1 to generate the optimized virtual call for invokeinterface
>> whose targets are the private interface methods.
>> 
>> Before JDK-823835, LambdaMetaFactory generates invokespecial in this case. Because the private
>> interface methods can not be overrided, c1 generates the optimized virtual call. After JDK-823835,
>> LambdaMetaFactory generates invokeinterface instead. C1 generates the regular virtual call because
>> it can not recognize the new pattern. If a multiple of subclasses all implement a same interface,
>> it is possible that they trash the IC stub using their own concrete klass in runtime.
>> 
>> Optimized virtual call uses relocInfo::opt_virtual_call_type(3), It will call VM
>> 'resolve_opt_virtual_call_C' once and resolve the target to the VEP of the nmethod.
>> Therefore, this patch can prevent the callsite from trashing.
>> 
>> Before this patch,   SlowStartupTest had 38770 times  _resolve_invoke_virtual_cnt and 38695  _handle_wrong_method_cnt per 10k iterations. To dump `C1Statistics`, we use fastdebug build for comparison.
>> 
>> 
>> $java -XX:TieredStopAtLevel=1 -XX:+PrintC1Statistics SlowStartupTest 1
>> Executed 10000 iterations in 736ms
>> C1 Runtime statistics:
>>  _resolve_invoke_virtual_cnt:     38770
>>  _resolve_invoke_opt_virtual_cnt: 186
>>  _resolve_invoke_static_cnt:      44
>>  _handle_wrong_method_cnt:        38695
>>  _ic_miss_cnt:                    35
>> 
>> 
>> With this patch,  only 1 _handle_wrong_method_cnt is triggered but we have 3 more `_resolve_invoke_opt_virtual_cnt` events instead.  The total runtime reduces from 736ms to 9ms. 
>> 
>> 
>> $java -XX:TieredStopAtLevel=1 -XX:+PrintC1Statistics SlowStartupTest 1
>> Executed 10000 iterations in 9ms
>> C1 Runtime statistics:
>>  _resolve_invoke_virtual_cnt:     77
>>  _resolve_invoke_opt_virtual_cnt: 189
>>  _resolve_invoke_static_cnt:      45
>>  _handle_wrong_method_cnt:        1
>>  _ic_miss_cnt:                    39
>> 
>> 
>> Codegen wise,  before the patch, C1 generates LIR for the invokeinterface whose target is a private interface methoda as follows.
>> 
>> __bci__use__tid____instr____________________________________
>> . 1    0    v2     a1.invokeinterface()
>>                    InvokePrivateInterfaceMethod$I.bar()V
>> . 6    0    v3     return
>> 
>> 
>> With this patch, C1 generates LIR as follows. it first check a1 is a subtype of `InvokePrivateInterfaceMethod$I`. if so, an optimized virtual call is generated. The callsite will be fixed up once and only one time in runtime. 
>> 
>> __bci__use__tid____instr____________________________________
>> . 1    1    a2     checkcast(a1) InvokePrivateInterfaceMethod$I
>>                    stack [0:a1]
>> . 1    0    v3     a2.invokeinterface()
>>                    InvokePrivateInterfaceMethod$I.bar()V
>> . 6    0    v4     return
>
> Xin Liu has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - 8274983: C1 optimizes the invocation of private interface methods
>  - Merge branch 'master' into JDK-8274983
>  - 8274983: Pattern.matcher performance regression after JDK-823835
>    
>    This patch allows c1 to generate the optimized virtual call for invokeinterface
>    whose targets are the private interface methods.
>    
>    Before JDK-823835, LambdaMetaFactory generates invokespecial in this case. Because the private
>    interface methods can not be overrided, c1 generates the optimized virtual call. After JDK-823835,
>    LambdaMetaFactory generates invokeinterface instead. C1 generates the regular virtual call because
>    it can not recognize the new pattern. If a multiple of subclasses all implement a same interface,
>    it is possible that they trash the IC stub using their own concrete klass in runtime.
>    
>    Optimized virtual call uses relocInfo::opt_virtual_call_type(3), It will call VM
>    'resolve_opt_virtual_call_C' once and resolve the target to the VEP of the nmethod.
>    Therefore, this patch can prevent the callsite from trashing.

Changes requested by dlong (Reviewer).

src/hotspot/share/c1/c1_GraphBuilder.cpp line 1902:

> 1900:       Value receiver = state()->stack_at(index);
> 1901:       CheckCast* c = new CheckCast(receiver_constraint, receiver, copy_state_before());
> 1902:       c->set_incompatible_class_change_check();

set_incompatible_class_change_check() seems OK for invokeinterface, but for invokespecial, I believe the interpreter throws IllegalAccessError.

-------------

PR: https://git.openjdk.java.net/jdk/pull/6445