Fix issue 825 (LiveEdit vs. function with no locals) in core and for ia32.

src/ia32/debug-ia32.cc

Index: src/ia32/debug-ia32.cc
diff --git a/src/ia32/debug-ia32.cc b/src/ia32/debug-ia32.cc
index 710cbaf19be318edf5c73408db650b84ae749487..901e38bfe3e33a855270d5ed107549a780291073 100644
--- a/src/ia32/debug-ia32.cc
+++ b/src/ia32/debug-ia32.cc
@@ -1,4 +1,4 @@
-// Copyright 2011 the V8 project authors. All rights reserved.
+// 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:
@@ -91,9 +91,11 @@ void BreakLocationIterator::ClearDebugBreakAtSlot() {
   rinfo()->PatchCode(original_rinfo()->pc(), Assembler::kDebugBreakSlotLength);
 }
 
+// All debug break stubs support padding for LiveEdit.
+const bool Debug::FramePaddingLayout::kIsSupported = true;
 
-#define __ ACCESS_MASM(masm)
 
+#define __ ACCESS_MASM(masm)
 
 static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
                                           RegList object_regs,
@@ -103,6 +105,13 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
   {
     FrameScope scope(masm, StackFrame::INTERNAL);
 
+    // Load padding words on stack.
+    for (int i = 0; i < Debug::FramePaddingLayout::kInitialSize; i++) {
+      __ push(Immediate(Smi::FromInt(
+          Debug::FramePaddingLayout::kPaddingValue)));
+    }
+    __ push(Immediate(Smi::FromInt(Debug::FramePaddingLayout::kInitialSize)));
+
     // 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 a smi causing it to be untouched by GC.
@@ -134,6 +143,10 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
     CEntryStub ceb(1);
     __ CallStub(&ceb);
 
+    // Automatically find register that could be used after register restore.
+    // We need one register for padding skip instructions.
+    Register unused_reg = { -1 };
+
     // Restore the register values containing object pointers from the
     // expression stack.
     for (int i = kNumJSCallerSaved; --i >= 0;) {
@@ -142,15 +155,29 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
       if (FLAG_debug_code) {
         __ Set(reg, Immediate(kDebugZapValue));
       }
+      bool taken = reg.code() == esi.code();
       if ((object_regs & (1 << r)) != 0) {
         __ pop(reg);
+        taken = true;
       }
       if ((non_object_regs & (1 << r)) != 0) {
         __ pop(reg);
         __ SmiUntag(reg);
+        taken = true;
+      }
+      if (!taken) {
+        unused_reg = reg;
       }
     }
 
+    ASSERT(unused_reg.code() != -1);
+
+    // Read current padding counter and skip corresponding number of words.
+    __ pop(unused_reg);
+    // We divide stored value by 2 (untagging) and multiply it by word's size.
+    STATIC_ASSERT(kSmiTagSize == 1);
+    __ lea(esp, Operand(esp, unused_reg, times_half_pointer_size, 0));
+
     // Get rid of the internal frame.
   }