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

src/x64/debug-x64.cc

Index: src/x64/debug-x64.cc
diff --git a/src/x64/debug-x64.cc b/src/x64/debug-x64.cc
index 94a50eb53e7731246dc135242ca92e889d975e90..6ef7e7befb737291f0f0c9466b1697a7f43646d5 100644
--- a/src/x64/debug-x64.cc
+++ b/src/x64/debug-x64.cc
@@ -91,7 +91,7 @@ void BreakLocationIterator::ClearDebugBreakAtSlot() {
   rinfo()->PatchCode(original_rinfo()->pc(), Assembler::kDebugBreakSlotLength);
 }
 
-const bool Debug::FramePaddingLayout::kIsSupported = false;
+const bool Debug::FramePaddingLayout::kIsSupported = true;
 
 
 #define __ ACCESS_MASM(masm)
@@ -105,6 +105,18 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
   {
     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.
@@ -159,6 +171,11 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
       }
     }
 
+    // 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.
   }