[Interpreter] Adds support to fetch return value on break at return.

src/debug/arm64/debug-arm64.cc

Index: src/debug/arm64/debug-arm64.cc
diff --git a/src/debug/arm64/debug-arm64.cc b/src/debug/arm64/debug-arm64.cc
index a2a6b733804d015add7121b5bd0160e888f5144f..f12dd29ec1fa366b7c9b4e887bb42014d7abe405 100644
--- a/src/debug/arm64/debug-arm64.cc
+++ b/src/debug/arm64/debug-arm64.cc
@@ -92,9 +92,15 @@ void DebugCodegen::GenerateDebugBreakStub(MacroAssembler* masm,
     __ Mov(scratch, Smi::FromInt(LiveEdit::kFramePaddingInitialSize));
     __ Push(scratch);
 
-    if (mode == SAVE_RESULT_REGISTER) __ Push(x0);
-
-    __ Mov(x0, 0);  // No arguments.
+    // Push arguments for DebugBreak call.
+    if (mode == SAVE_RESULT_REGISTER) {
+      // Break on return.
+      __ Push(x0);
+    } else {
+      // Non-return breaks.
+      __ Push(masm->isolate()->factory()->the_hole_value());
+    }
+    __ Mov(x0, 1);
     __ Mov(x1, ExternalReference(Runtime::FunctionForId(Runtime::kDebugBreak),
                                  masm->isolate()));
 
@@ -104,13 +110,14 @@ void DebugCodegen::GenerateDebugBreakStub(MacroAssembler* masm,
     if (FLAG_debug_code) {
       for (int i = 0; i < kNumJSCallerSaved; i++) {
         Register reg = Register::XRegFromCode(JSCallerSavedCode(i));
-        __ Mov(reg, Operand(kDebugZapValue));
+        // Do not clobber x0 if SAVE_RESULT_REGISTER is set. It will
+        // contain return value of the function.
+        if (!(reg.is(x0) && SAVE_RESULT_REGISTER)) {
+          __ Mov(reg, Operand(kDebugZapValue));
+        }
       }
     }
 
-    // Restore the register values from the expression stack.
-    if (mode == SAVE_RESULT_REGISTER) __ Pop(x0);
-
     // Don't bother removing padding bytes pushed on the stack
     // as the frame is going to be restored right away.