What is faster, imm64 or m64 for x86-64?

Question

After testing, about 10 billion times, if imm640.1 nanoseconds faster than m64for AMD64, m64it seems faster, but I really don't understand. Is the address val_ptrin the following code an immediate value?

# Text section
.section __TEXT,__text,regular,pure_instructions
# 64-bit code
.code64
# Intel syntax
.intel_syntax noprefix
# Target macOS High Sierra
.macosx_version_min 10,13,0

# Make those two test functions global for the C measurer
.globl _test1
.globl _test2

# Test 1, imm64
_test1:
  # Move the immediate value 0xDEADBEEFFEEDFACE to RAX (return value)
  movabs rax, 0xDEADBEEFFEEDFACE
  ret
# Test 2, m64
_test2:
  # Move from the RAM (val_ptr) to RAX (return value)
  mov rax, qword ptr [rip + val_ptr]
  ret
# Data section
.section __DATA,__data
val_ptr:
  .quad 0xDEADBEEFFEEDFACE

Measurement Code:

#include <stdio.h>            // For printf
#include <stdlib.h>           // For EXIT_SUCCESS
#include <math.h>             // For fabs
#include <stdint.h>           // For uint64_t
#include <stddef.h>           // For size_t
#include <string.h>           // For memset
#include <mach/mach_time.h>   // For time stuff

#define FUNCTION_COUNT  2     // Number of functions to test
#define TEST_COUNT      0x10000000  // Number of times to test each function

// Type aliases
typedef uint64_t rettype_t;
typedef rettype_t(*function_t)();

// External test functions (defined in Assembly)
rettype_t test1();
rettype_t test2();

// Program entry point
int main() {

  // Time measurement stuff
  mach_timebase_info_data_t info;
  mach_timebase_info(&info);

  // Sums to divide by the test count to get average
  double sums[FUNCTION_COUNT];

  // Initialize sums to 0
  memset(&sums, 0, FUNCTION_COUNT * sizeof (double));

  // Functions to test
  function_t functions[FUNCTION_COUNT] = {test1, test2};

  // Useless results (should be 0xDEADBEEFFEEDFACE), but good to have
  rettype_t results[FUNCTION_COUNT];

  // Function loop, may get unrolled based on optimization level
  for (size_t test_fn = 0; test_fn < FUNCTION_COUNT; test_fn++) {
    // Test this MANY times
    for (size_t test_num = 0; test_num < TEST_COUNT; test_num++) {
      // Get the nanoseconds before the action
      double nanoseconds = mach_absolute_time();
      // Do the action
      results[test_fn] = functions[test_fn]();
      // Measure the time it took
      nanoseconds = mach_absolute_time() - nanoseconds;

      // Convert it to nanoseconds
      nanoseconds *= info.numer;
      nanoseconds /= info.denom;

      // Add the nanosecond count to the sum
      sums[test_fn] += nanoseconds;
    }
  }
  // Compute the average
  for (size_t i = 0; i < FUNCTION_COUNT; i++) {
    sums[i] /= TEST_COUNT;
  }

  if (FUNCTION_COUNT == 2) {
    // Print some fancy information
    printf("Test 1 took %f nanoseconds average.\n", sums[0]);
    printf("Test 2 took %f nanoseconds average.\n", sums[1]);
    printf("Test %d was faster, with %f nanoseconds difference\n", sums[0] < sums[1] ? 1 : 2, fabs(sums[0] - sums[1]));
  } else {
    // Else, just print something
    for (size_t fn_i = 0; fn_i < FUNCTION_COUNT; fn_i++) {
      printf("Test %zu took %f clock ticks average.\n", fn_i + 1, sums[fn_i]);
    }
  }

  // Everything went fine!
  return EXIT_SUCCESS;
}

So what is really faster, m64or imm64?

By the way, I use Intel I7 Ivy Bridge and DDR3 RAM. I am running macOS High Sierra.

EDIT : I entered the instructions retand now imm64turned out to be faster.

Answer 1

, , - , . -, , ( ). , /, ( i7).

---

Intel IvyBridge:

movabs rax, 0xDEADBEEFFEEDFACE ALU

• 10 ( ).
• 1 uop ALU (p0, p1 p5). ( = 3 )
• 2 uop (- 64-) 2 uop. ( , , , ).

mov rax, [RIP + val_ptr]

• 7 (REX + + modrm + rel32)
• 1 uop (p2 p3). ( = 2 )
• 1 uop ( 32 32- ).
• , , Skylake.
• .

: Agtern Fog microarch pdf . . 9.1 uop-cache. . x86 .

---

64- mov r64, imm64. (Related: " " ?, , 64- -1.)

, , , , , , .rodata. , - and rax, [constant] movabs r8, imm64/and rax, r8.

64- , RIP-relative lea , . lea rax, [rel my_symbol] NASM, lea my_symbol(%rip), %rax AT & T.

---

asm, .