Example of HotSpot 25's C1 compiling a MethodHandle (Part I): unable to inline, because root of compilation is the invokeExact() itself, and it can't see the MH is a "constant".

.hotspot_compiler

exclude java/io/* *
exclude java/nio/* *
exclude java/util/* *
exclude java/lang/StringBuilder *
exclude java/lang/String *
exclude java/lang/Integer *
exclude java/lang/AbstractStringBuilder *

.hotspotrc

TieredStopAtLevel=1
CICompilerCount=1
CompileThreshold=1000
-BackgroundCompilation
+PrintVMOptions
+PrintCompilation
+PrintInlining

# The following 2 flags go together, they're used to trust
# final instance fields marked with @Stable as constants
#+UnlockExperimentalVMOptions
#+TrustFinalNonStaticFields
#+FoldStableValues

c1.patch

diff -r a632dd6ef1f9 src/share/vm/c1/c1_GraphBuilder.cpp
--- a/src/share/vm/c1/c1_GraphBuilder.cpp	Mon Dec 16 00:44:46 2013 -0800
+++ b/src/share/vm/c1/c1_GraphBuilder.cpp	Mon Dec 23 17:32:22 2013 -0800
@@ -4015,6 +4015,9 @@
       // get MethodHandle receiver
       const int args_base = state()->stack_size() - callee->arg_size();
       ValueType* type = state()->stack_at(args_base)->type();
+      tty->print(__FILE__ ":%d: type = ", __LINE__);
+      type->print();
+      tty->print_cr(" %s", type->is_constant() ? "is constant" : "not constant");
       if (type->is_constant()) {
         ciMethod* target = type->as_ObjectType()->constant_value()->as_method_handle()->get_vmtarget();
         // We don't do CHA here so only inline static and statically bindable methods.

MHTest.java

import java.lang.invoke.*;
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;

public class MHTest {
  private static final Lookup LK = lookup();
  private static final MethodHandle MH0;
  private static final MethodHandle MH1;
  
  static {
    MethodHandle mh0 = null;
    MethodHandle mh1 = null;
    try {
      mh0 = LK.findStatic(LK.lookupClass(),
                         "foo",
                         methodType(int.class,
                                    int.class, int.class));
      mh1 = insertArguments(mh0, 1, 42);
    } catch (Throwable t) {
      t.printStackTrace();
    }
    MH0 = mh0;
    MH1 = mh1;
  }
  
  public static int foo(int x, int y) {
    // System.out.println("x: " + x + ", y: " + y);
    return x + y;
  }

  public static void main(String[] args) throws Throwable {
    for (int i = 0; i < 1200; i++) {
      int dummy = (int) MH1.invokeExact(0);
    }
  }
}

PrintCompilation.log

    504  132    b  1       java.lang.invoke.LambdaForm$MH/1414644648::invokeExact_MT (14 bytes)
                              @ 2   java.lang.invoke.Invokers::checkExactType (30 bytes)   force inline by annotation
                                @ 11   java.lang.invoke.MethodHandle::type (5 bytes)
                                @ 25   java.lang.invoke.Invokers::newWrongMethodTypeException (36 bytes)   callee is too large
/Users/krismo/code/hotspot-comp/hotspot/src/share/vm/c1/c1_GraphBuilder.cpp:4018: type = object not constant
                              @ 10   java.lang.invoke.MethodHandle::invokeBasic(I)I (0 bytes)   receiver not constant
    505  133    b  1       java.lang.invoke.Invokers::checkExactType (30 bytes)
                              @ 11   java.lang.invoke.MethodHandle::type (5 bytes)
                              @ 25   java.lang.invoke.Invokers::newWrongMethodTypeException (36 bytes)   callee is too large
    506  134    b  1       java.lang.invoke.BoundMethodHandle$Species_LI::reinvokerTarget (8 bytes)
    506  135    b  1       MHTest::foo (4 bytes)
    507  136    b  1       java.lang.invoke.LambdaForm$DMH/621009875::invokeStatic_II_I (15 bytes)
                              @ 1   java.lang.invoke.DirectMethodHandle::internalMemberName (8 bytes)   force inline by annotation
                              @ 11   java.lang.invoke.MethodHandle::linkToStatic(IIL)I (0 bytes)   MemberName not constant
    508  137    b  1       java.lang.invoke.LambdaForm$BMH/1072591677::reinvoke (26 bytes)
                              @ 12   java.lang.invoke.MethodHandle::reinvokerTarget (42 bytes)   no static binding
/Users/krismo/code/hotspot-comp/hotspot/src/share/vm/c1/c1_GraphBuilder.cpp:4018: type = object not constant
                              @ 22   java.lang.invoke.MethodHandle::invokeBasic(II)I (0 bytes)   receiver not constant

run.sh

#!/bin/sh

# -Djava.lang.invoke.MethodHandle.COMPILE_THRESHOLD=2
java -XX:Flags=.hotspotrc -XX:CompileCommandFile=.hotspot_compiler MHTest