RFR: 8295537: Debug tracing for resolved java.lang.invoke.CallSite

[Jorn Vernee]

On Tue, 25 Oct 2022 12:50:05 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> I've added a `java.lang.invoke.MethodHandle.TRACE_CALLSITE` property to show how invokedynamic call sites are resolved.
>> 
>> For example:
>> 
>> 
>> public class StrConcat {
>>     static String hello = "Hello";
>>     static String world = "World";
>>     public static void main(String args[]) {
>>         System.out.println(hello + world);
>>         System.out.println(hello + "World");
>>     }
>> }
>> 
>> $ java -Djava.lang.invoke.MethodHandle.TRACE_CALLSITE=true -cp . StrConcat
>> ======== CallSite: StrConcat.main(StrConcat.java:5)
>> BSM = java.base/java.lang.invoke.StringConcatFactory.makeConcatWithConstants(StringConcatFactory.java:354)
>> target class = java.lang.invoke.BoundMethodHandle$Species_L
>> target = (String,String)String : BMH.reinvoke=Lambda(a0:L/SpeciesData[L => Species_L],a1:L,a2:L)=>{
>>     t3:L=Species_L.argL0(a0:L);
>>     t4:L=MethodHandle.invokeBasic(t3:L,a1:L,a2:L);t4:L}
>> & BMH=[
>>   0: MethodHandle = {(Object,Object)String : DMH.invokeStatic=Lambda(a0:L,a1:L,a2:L)=>{
>>         t3:L=DirectMethodHandle.internalMemberName(a0:L);
>>         t4:L=MethodHandle.linkToStatic(a1:L,a2:L,t3:L);t4:L}
>>     & DMH.MN=java.lang.StringConcatHelper.simpleConcat(Object,Object)String/invokeStatic
>>   }
>> ]
>> HelloWorld
>> ======== CallSite: StrConcat.main(StrConcat.java:6)
>> BSM = java.base/java.lang.invoke.StringConcatFactory.makeConcatWithConstants(StringConcatFactory.java:354)
>> target class = java.lang.invoke.BoundMethodHandle$Species_LL
>> target = (String)String : invoke=Lambda(a0:L/SpeciesData[LL => BoundMethodHandle$Species_LL],a1:L)=>{
>>     t2:L=BoundMethodHandle$Species_LL.argL1(a0:L);
>>     t3:L=BoundMethodHandle$Species_LL.argL0(a0:L);
>>     t4:L=MethodHandle.invokeBasic(t3:L,a1:L,t2:L);t4:L}
>> & BMH=[
>>   0: MethodHandle = {(Object,Object)String : DMH.invokeStatic=Lambda(a0:L,a1:L,a2:L)=>{
>>         t3:L=DirectMethodHandle.internalMemberName(a0:L);
>>         t4:L=MethodHandle.linkToStatic(a1:L,a2:L,t3:L);t4:L}
>>     & DMH.MN=java.lang.StringConcatHelper.simpleConcat(Object,Object)String/invokeStatic
>>   }
>>   1: ( World )
>> ]
>> HelloWorld
>> 
>> 
>> More complex examples are in the JBS bug report
>> - https://bugs.openjdk.org/secure/attachment/101170/eclipse-ide-log.txt
>> - https://bugs.openjdk.org/secure/attachment/101168/lambda-expression.txt
>> - https://bugs.openjdk.org/secure/attachment/101174/pattern-matching-switch.txt
>> - https://bugs.openjdk.org/secure/attachment/101169/str-concat.txt
>
> src/java.base/share/classes/java/lang/invoke/MethodHandle.java line 1814:
> 
>> 1812:             return "";
>> 1813:         }
>> 1814:         return new String(new char[indentLevel*4]).replace('\0', ' ');
> 
> I guess this could be:
> Suggestion:
> 
>         return "    ".repeat(indentLevel);

Alternatively, I was gonna suggest not having a prefix/indentLevel and instead calling `String::indent` at the use site. But, that method uses streams/lambdas, so there might be boostrap cycle issues.

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PR: https://git.openjdk.org/jdk/pull/10842