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

src/debug/mips/debug-mips.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_MIPS
 
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 
 namespace v8 {
@@ skipping 59 matching lines @@
     // Load padding words on stack.
     __ li(at, Operand(Smi::FromInt(LiveEdit::kFramePaddingValue)));
     __ Subu(sp, sp,
             Operand(kPointerSize * LiveEdit::kFramePaddingInitialSize));
     for (int i = LiveEdit::kFramePaddingInitialSize - 1; i >= 0; i--) {
       __ sw(at, MemOperand(sp, kPointerSize * i));
     }
     __ li(at, Operand(Smi::FromInt(LiveEdit::kFramePaddingInitialSize)));
     __ push(at);
 
-    if (mode == SAVE_RESULT_REGISTER) __ push(v0);
-
-    __ PrepareCEntryArgs(0);  // No arguments.
+    // Push arguments for DebugBreak call.
+    if (mode == SAVE_RESULT_REGISTER) {
+      // Break on return.
+      __ push(v0);
+    } else {
+      // Non-return breaks.
+      __ Push(masm->isolate()->factory()->the_hole_value());
+    }
+    __ PrepareCEntryArgs(1);
     __ PrepareCEntryFunction(ExternalReference(
         Runtime::FunctionForId(Runtime::kDebugBreak), masm->isolate()));
 
     CEntryStub ceb(masm->isolate(), 1);
     __ CallStub(&ceb);
 
     if (FLAG_debug_code) {
       for (int i = 0; i < kNumJSCallerSaved; i++) {
         Register reg = {JSCallerSavedCode(i)};
-        __ li(reg, kDebugZapValue);
+        // Do not clobber v0 if SAVE_RESULT_REGISTER is set. It will
+        // contain return value of the function returned by DebugBreak.
+        if (!(reg.is(v0) && SAVE_RESULT_REGISTER)) {
+          __ li(reg, kDebugZapValue);
+        }
       }
     }
 
-    if (mode == SAVE_RESULT_REGISTER) __ pop(v0);
-
     // Don't bother removing padding bytes pushed on the stack
     // as the frame is going to be restored right away.
 
     // Leave the internal frame.
   }
 
   // Now that the break point has been handled, resume normal execution by
   // jumping to the target address intended by the caller and that was
   // overwritten by the address of DebugBreakXXX.
   ExternalReference after_break_target =
@@ skipping 31 matching lines @@
 
 
 const bool LiveEdit::kFrameDropperSupported = true;
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS