Minor code clean up and add changelog entry.

Author: aardvark179

CHANGELOG.md

@@ -55,6 +55,7 @@ Performance:
 * Calls with a literal block are no longer always split but instead the decision is made by the Truffle splitting heuristic.
 * `Symbol#to_proc` is now AST-inlined in order to not rely on splitting and to avoid needing the caller frame to find refinements which apply.
 * `Symbol#to_proc` is now globally cached per Symbol and refinements, to avoid creating many redundant `CallTargets`.
+* Setting and access to the special variables `$~` and `$_` has been refactored to require less splitting.
 
 Changes:
 

src/main/java/org/truffleruby/core/kernel/TruffleKernelNodes.java

@@ -188,7 +188,7 @@ public abstract static class GetSpecialVariableStorage extends RubyContextNode {
         public abstract SpecialVariableStorage execute(VirtualFrame frame);
 
         @Specialization(
-                guards = { "frame.getFrameDescriptor() == descriptor", "declarationFrameSlot != null" },
+                guards = "frame.getFrameDescriptor() == descriptor",
                 assumptions = "frameAssumption",
                 limit = "1")
         protected SpecialVariableStorage getFromKnownFrameDescriptor(VirtualFrame frame,
@@ -273,13 +273,11 @@ protected int declarationDepth(VirtualFrame topFrame) {
         }
 
         protected FrameDescriptor declarationDescriptor(VirtualFrame topFrame, int depth) {
-            MaterializedFrame frame;
             if (depth == 0) {
-                frame = topFrame.materialize();
+                return topFrame.getFrameDescriptor();
             } else {
-                frame = RubyArguments.getDeclarationFrame(topFrame, depth);
+                return RubyArguments.getDeclarationFrame(topFrame, depth).getFrameDescriptor();
             }
-            return frame.getFrameDescriptor();
         }
 
         @TruffleBoundary

src/main/java/org/truffleruby/language/backtrace/BacktraceFormatter.java

@@ -114,7 +114,7 @@ public void printRubyExceptionOnEnvStderr(String info, RubyException rubyExcepti
                 context.getCoreLibrary().truffleExceptionOperationsModule,
                 "get_formatted_backtrace",
                 rubyException);
-        final String formatted = fullMessage != null ? ((RubyString) fullMessage).getJavaString() : "";
+        final String formatted = fullMessage != null ? ((RubyString) fullMessage).getJavaString() : "<no message>";
         if (formatted.endsWith("\n")) {
             printer.print(formatted);
         } else {