Small rethink of method handles for reentry

Turns out we can't just use invokeExact on the original method because the
type is different for every compilation unit, duh.  So let's pre-curry and
cache an appropriate form of the method on the StaticCodeInfo.

src/vm/jvm/QAST/Compiler.nqp

@@ -62,6 +62,7 @@ my $TYPE_EX_CONT   := 'Lorg/perl6/nqp/runtime/ControlException;';
 my $TYPE_EX_RT     := 'Ljava/lang/RuntimeException;';
 my $TYPE_EX_SAVE   := 'Lorg/perl6/nqp/runtime/SaveStackException;';
 my $TYPE_THROWABLE := 'Ljava/lang/Throwable;';
+my $TYPE_RESUME    := 'Lorg/perl6/nqp/runtime/ResumeStatus;';
 
 # Exception handler categories.
 my $EX_CAT_CATCH   := 1;
@@ -3054,6 +3055,7 @@ class QAST::CompilerJAST {
             $*JMETH.add_argument('cr', $TYPE_CR);
             $*JMETH.add_argument('csd', $TYPE_CSD);
             $*JMETH.add_argument('__args', "[$TYPE_OBJ");
+            $*JMETH.add_argument('resume', $TYPE_RESUME);
 
             # Set up temporaries allocator.
             my $*BLOCK_TA := BlockTempAlloc.new();
@@ -3264,7 +3266,7 @@ class QAST::CompilerJAST {
             if $block.num_save_sites {
                 my $saver := JAST::InstructionList.new;
                 $saver.append(JAST::Label.new( :name( 'SAVER' ) ));
-                $saver.append(JAST::PushCurMeth.new);
+                $saver.append($ACONST_NULL);
 
                 my @merged;
                 for $*JMETH.arguments { nqp::push(@merged, $_); }
@@ -3338,12 +3340,13 @@ class QAST::CompilerJAST {
                     $TYPE_OPS, 'emptyCallSite', $TYPE_CSD ));
                 $il.append(JAST::Instruction.new( :op('getstatic'),
                     $TYPE_OPS, 'emptyArgList', "[$TYPE_OBJ" ));
+                $il.append($ACONST_NULL);
 
                 # Emit the virtual call.
                 $il.append(savesite(JAST::Instruction.new( :op('invokevirtual'),
                     'L' ~ $*JCLASS.name ~ ';',
                     $*CODEREFS.cuid_to_jastmethname($node.cuid),
-                    'V', $TYPE_TC, $TYPE_CR, $TYPE_CSD, "[$TYPE_OBJ" )));
+                    'V', $TYPE_TC, $TYPE_CR, $TYPE_CSD, "[$TYPE_OBJ", $TYPE_RESUME )));
 
                 # Load result onto the stack, unless in void context.
                 if $*WANT != $RT_VOID {

src/vm/jvm/QAST/JASTNodes.nqp

@@ -367,15 +367,6 @@ class JAST::PushCVal is JAST::Node {
     method dump() { ".push_cc $!value" }
 }
 
-class JAST::PushCurMeth is JAST::Node {
-    method new() {
-        my $node := nqp::create(JAST::PushCurMeth);
-        $node
-    }
-
-    method dump() { ".push_cur_meth" }
-}
-
 class JAST::TryCatch is JAST::Node {
     has $!try;
     has $!catch;

src/vm/jvm/runtime/org/perl6/nqp/runtime/SaveStackException.java

@@ -16,7 +16,9 @@ public SaveStackException(int tag) {
     }
 
     public SaveStackException pushFrame(int resumePoint, MethodHandle method, Object[] saveSpace, CallFrame callFrame) {
+        if (method == null) method = callFrame.codeRef.staticInfo.mhResume;
         top = new ResumeStatus.Frame(method, resumePoint, saveSpace, callFrame, top);
+        if (callFrame != null) callFrame.tc.curFrame = callFrame.caller;
         return this;
     }
 }

src/vm/jvm/runtime/org/perl6/nqp/runtime/StaticCodeInfo.java

@@ -1,6 +1,8 @@
 package org.perl6.nqp.runtime;
 
 import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
 import java.util.HashMap;
 
 import org.perl6.nqp.sixmodel.SixModelObject;
@@ -15,6 +17,11 @@ public class StaticCodeInfo implements Cloneable {
      * Method handle for the code ref.
      */
     MethodHandle mh;
+
+    /**
+     * Curried method handle for resuming.
+     */
+    MethodHandle mhResume;
 
     /**
      * The (human-readable) name of the code-ref.
@@ -139,6 +146,11 @@ public StaticCodeInfo(CompilationUnit compUnit, MethodHandle mh,
             this.oLexStatic = new SixModelObject[oLexicalNames.length];
             this.oLexStaticFlags = new byte[oLexicalNames.length];
         }
+        MethodType t = mh.type();
+        if (t.parameterCount() == 5 && t.parameterType(4) == ResumeStatus.class) {
+            mhResume = MethodHandles.insertArguments(mh, 0, null, null, null, null);
+            this.mh = MethodHandles.insertArguments(mh, 4, (Object)null);
+        }
     }
 
     public StaticCodeInfo clone() {