Comparison between call by reference and call by value

gistfile1.cpp

The Code:

int add_ref(const int& a, const int& b)
{
  return a + b;
}

int add_value(const int a, const int b)
{
  return a + b;
}
----------------------------------------------------------------------------
Compile with:
clang++ -O3 -S -mllvm --x86-asm-syntax=intel hoge.cpp -o hoge.intel.s

where
clang++ -v
Apple LLVM version 4.2 (clang-425.0.24) (based on LLVM 3.2svn)
Target: x86_64-apple-darwin12.2.0
----------------------------------------------------------------------------
The Result (simpilified):

__Z7add_refRKiS0_:                      ## @_Z7add_refRKiS0_
	push	RBP
	mov	RBP, RSP
	mov	EAX, DWORD PTR [RSI]
	add	EAX, DWORD PTR [RDI]
	pop	RBP
	ret

__Z9add_valueii:                        ## @_Z9add_valueii
	push	RBP
	mov	RBP, RSP
	add	EDI, ESI
	mov	EAX, EDI
	pop	RBP
	ret