Fix issue 825 (LiveEdit vs. function with no locals) for x64.

src/x64/debug-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 73 matching lines @@
       Isolate::Current()->debug()->debug_break_slot()->entry(),
       Assembler::kDebugBreakSlotLength - Assembler::kCallInstructionLength);
 }
 
 
 void BreakLocationIterator::ClearDebugBreakAtSlot() {
   ASSERT(IsDebugBreakSlot());
   rinfo()->PatchCode(original_rinfo()->pc(), Assembler::kDebugBreakSlotLength);
 }
 
-const bool Debug::FramePaddingLayout::kIsSupported = false;
+const bool Debug::FramePaddingLayout::kIsSupported = true;
 
 
 #define __ ACCESS_MASM(masm)
 
 
 static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
                                           RegList object_regs,
                                           RegList non_object_regs,
                                           bool convert_call_to_jmp) {
   // Enter an internal frame.
   {
     FrameScope scope(masm, StackFrame::INTERNAL);
 
+    // Load padding words on stack.
+    __ movq(kScratchRegister,
+        Immediate(Debug::FramePaddingLayout::kPaddingValue));
+    __ Integer32ToSmi(kScratchRegister, kScratchRegister);
+    for (int i = 0; i < Debug::FramePaddingLayout::kInitialSize; i++) {
+      __ push(kScratchRegister);
+    }
+    __ movq(kScratchRegister,
+        Immediate(Debug::FramePaddingLayout::kInitialSize));
+    __ Integer32ToSmi(kScratchRegister, kScratchRegister);

[Yang, 2012/05/16 09:59:01]

You can convert those values to smi using
    Smi* value = Smi::FromInt(123);
and then use MacroAssembler::Push(Smi*) to push them onto the stack. This way
you avoid smi conversions at runtime.

[Peter Rybin, 2012/05/16 21:14:57]

And this is 2-6 times shorter in terms of generated code size!
Done

+    __ push(kScratchRegister);
+
     // Store the registers containing live values on the expression stack to
     // make sure that these are correctly updated during GC. Non object values
     // are stored as as two smis causing it to be untouched by GC.
     ASSERT((object_regs & ~kJSCallerSaved) == 0);
     ASSERT((non_object_regs & ~kJSCallerSaved) == 0);
     ASSERT((object_regs & non_object_regs) == 0);
     for (int i = 0; i < kNumJSCallerSaved; i++) {
       int r = JSCallerSavedCode(i);
       Register reg = { r };
       ASSERT(!reg.is(kScratchRegister));
@@ skipping 34 matching lines @@
       if ((non_object_regs & (1 << r)) != 0) {
         __ pop(kScratchRegister);
         __ SmiToInteger32(kScratchRegister, kScratchRegister);
         __ shl(kScratchRegister, Immediate(32));
         __ pop(reg);
         __ SmiToInteger32(reg, reg);
         __ or_(reg, kScratchRegister);
       }
     }
 
+    // Read current padding counter and skip corresponding number of words.
+    __ pop(kScratchRegister);
+    __ SmiToInteger32(kScratchRegister, kScratchRegister);
+    __ lea(rsp, Operand(rsp, kScratchRegister, times_pointer_size, 0));
+
     // Get rid of the internal frame.
   }
 
   // If this call did not replace a call but patched other code then there will
   // be an unwanted return address left on the stack. Here we get rid of that.
   if (convert_call_to_jmp) {
     __ addq(rsp, Immediate(kPointerSize));
   }
 
   // Now that the break point has been handled, resume normal execution by
@@ skipping 162 matching lines @@
 
 const bool Debug::kFrameDropperSupported = true;
 
 #undef __
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64