Remove extra RubyProc cast in ReadBlockFromCurrentFrameArgumentsNode

Author: eregon

src/main/java/org/truffleruby/language/arguments/ReadBlockFromCurrentFrameArgumentsNode.java

@@ -9,7 +9,6 @@
  */
 package org.truffleruby.language.arguments;
 
-import org.truffleruby.core.proc.RubyProc;
 import org.truffleruby.language.RubyContextSourceNode;
 
 import com.oracle.truffle.api.frame.VirtualFrame;
@@ -27,7 +26,7 @@ public ReadBlockFromCurrentFrameArgumentsNode(Object valueIfAbsent) {
 
     @Override
     public Object execute(VirtualFrame frame) {
-        final RubyProc block = RubyArguments.getBlock(frame);
+        final Object block = RubyArguments.getBlockAssertType(frame);
         return nullProfile.profile(block == null) ? valueIfAbsent : block;
     }
 

src/main/java/org/truffleruby/language/arguments/RubyArguments.java

@@ -150,6 +150,13 @@ public static RubyProc getBlock(Frame frame) {
         return (RubyProc) frame.getArguments()[ArgumentIndicies.BLOCK.ordinal()];
     }
 
+    /** A variant of getBlock() when the return type does not need to be RubyProc and which avoids the extra cast. */
+    public static Object getBlockAssertType(Frame frame) {
+        final Object block = frame.getArguments()[ArgumentIndicies.BLOCK.ordinal()];
+        assert block == null || block instanceof RubyProc : block;
+        return block;
+    }
+
     public static int getArgumentsCount(Frame frame) {
         return frame.getArguments().length - RUNTIME_ARGUMENT_COUNT;
     }