restrict in c99

restrict.txt

WITHOUT RESTRICT:

$ echo "void frob(unsigned char* first, unsigned char* second, unsigned int count) { 
   for(int i = 0; i < count; ++i ) { 
      first[i] = second[i]; 
   } 
}" | clang -cc1 -O3 -S -x c -std=c99 -

_frob:
  testl	%edx, %edx
	je	LBB0_2
LBB0_1:
	movb	(%rsi), %al
	movb	%al, (%rdi)
	incq	%rsi
	incq	%rdi
	decl	%edx
	jne	LBB0_1
LBB0_2:
	ret

WITH RESTRICT:
 
$ echo "void frob(unsigned char* restrict first, unsigned char* restrict second, unsigned int count) { 
   for(int i = 0; i < count; ++i ) { 
      first[i] = second[i]; 
   } 
}" | clang -cc1 -O3 -S -x c -std=c99  -
 
	.align	4, 0x90
_frob:
	pushq	%rax
	testl	%edx, %edx
	je	LBB0_2
	decl	%edx
	incq	%rdx
	callq	_memcpy
LBB0_2:
	popq	%rax
	ret