To fully support hydrogen code stubs which accept a variable number of arguments,

src/ia32/lithium-codegen-ia32.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 2718 matching lines @@
       JavaScriptFrameConstants::kDynamicAlignmentStateOffset));
   }
   if (NeedsEagerFrame()) {
     __ mov(esp, ebp);
     __ pop(ebp);
   }
   if (dynamic_frame_alignment_) {
     Label no_padding;
     __ cmp(edx, Immediate(kNoAlignmentPadding));
     __ j(equal, &no_padding);
-    if (FLAG_debug_code) {
-      __ cmp(Operand(esp, (GetParameterCount() + 2) * kPointerSize),
-             Immediate(kAlignmentZapValue));
-      __ Assert(equal, "expected alignment marker");
+
+    if (instr->has_constant_parameter_count()) {
+      if (FLAG_debug_code) {

[danno, 2013/03/07 15:11:14]

Can't you combine this code path with the one below?
You just need to insert an "__ inc(reg)" or use an adjusted parameter constant
count if dynamic_frame_alignment_ is true.

[mvstanton, 2013/03/07 16:48:49]

Done.

+        __ cmp(Operand(esp,
+                       (instr->constant_parameter_count() + 2) * kPointerSize),
+               Immediate(kAlignmentZapValue));
+        __ Assert(equal, "expected alignment marker");
+      }
+      __ Ret((instr->constant_parameter_count() + 2) * kPointerSize, ecx);
+    } else {
+      Register reg = ToRegister(instr->parameter_count());
+      Register temp_reg = reg.is(ecx) ? ebx : ecx;
+      if (FLAG_debug_code) {
+        __ cmp(Operand(esp, reg, times_pointer_size, 2 * kPointerSize),
+               Immediate(kAlignmentZapValue));
+        __ Assert(equal, "expected alignment marker");
+      }
+
+      // emit code to restore stack based on instr->parameter_count()
+      __ pop(temp_reg);  // save return address
+      __ inc(reg);  // 1 more for alignment
+      __ shl(reg, kPointerSizeLog2);
+      __ add(esp, reg);
+      __ jmp(temp_reg);
     }
-    __ Ret((GetParameterCount() + 2) * kPointerSize, ecx);
     __ bind(&no_padding);
   }
-  if (info()->IsStub()) {
-    __ Ret();
+
+  if (instr->has_constant_parameter_count()) {

[danno, 2013/03/07 15:11:14]

if (instr->parameter_count()->IsConstantOperand())

[mvstanton, 2013/03/07 16:48:49]

Done.

+    __ Ret((instr->constant_parameter_count() + 1) * kPointerSize, ecx);

[danno, 2013/03/07 15:11:14]

int32_t parameter_count =
ToInteger32(LConstantOperand::cast(instr->parameter_count()));

[mvstanton, 2013/03/07 16:48:49]

Done.

   } else {
-    __ Ret((GetParameterCount() + 1) * kPointerSize, ecx);
+    Register reg = ToRegister(instr->parameter_count());
+    Register return_addr_reg = reg.is(ecx) ? ebx : ecx;
+    __ pop(return_addr_reg);  // save return address
+    __ shl(reg, kPointerSizeLog2);
+    __ add(esp, reg);
+    __ jmp(return_addr_reg);
   }
 }
 
 
 void LCodeGen::DoLoadGlobalCell(LLoadGlobalCell* instr) {
   Register result = ToRegister(instr->result());
   __ mov(result, Operand::Cell(instr->hydrogen()->cell()));
   if (instr->hydrogen()->RequiresHoleCheck()) {
     __ cmp(result, factory()->the_hole_value());
     DeoptimizeIf(equal, instr->environment());
@@ skipping 3498 matching lines @@
                               FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32