code:

> cc --version && cat add.c && cc -std=c11 -W -Wall -pedantic -march=native -pedantic -O3 -c add.c && objdump -d add.o
gcc (Raspbian 8.3.0-6+rpi1) 8.3.0
...
#include <stdint.h>

uint64_t add_ints(const uint64_t a, const uint64_t b) {
  return a + b;
}

uint64_t add_array(const uint64_t * const a) {
  return a[0] + a[1];
}

add.o:     file format elf32-littlearm
Disassembly of section .text:

00000000 <add_ints>:
   0:	e0900002 	adds	r0, r0, r2
   4:	e0a11003 	adc	r1, r1, r3
   8:	e12fff1e 	bx	lr

0000000c <add_array>:
   c:	e5903000 	ldr	r3, [r0]
  10:	e5902008 	ldr	r2, [r0, #8]
  14:	e590c004 	ldr	ip, [r0, #4]
  18:	e590100c 	ldr	r1, [r0, #12]
  1c:	e0930002 	adds	r0, r3, r2
  20:	e0ac1001 	adc	r1, ip, r1
  24:	e12fff1e 	bx	lr