The latest version of gcc is producing assembly that doesn't make sense to me. I compiled the code using no optimization; but, some parts of this code don't make sense, even with no optimization.

Here is the C source:

  #include <stdio.h>

   int main()
   {
     int a = 1324;
     int b = 5657;
     int difference = 9876;
     int printf_answer = 2221;

     difference = a - b;

     printf_answer = printf("%d + %d = %d\n", a, b, difference);

     return difference;
   }

It produces this assembly:

    .file   "exampleIML-1b.c"
    .section    .rodata
.LC0:
    .string "%d + %d = %d\n"
    .text
.globl main
    .type   main, @function
main:
.LFB0:
    .cfi_startproc
    pushq   %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    pushq   %rbx
    subq    $24, %rsp
    movl    $1324, -32(%rbp)
    movl    $5657, -28(%rbp)
    movl    $9876, -24(%rbp)
    movl    $2221, -20(%rbp)
    movl    -28(%rbp), %eax
    movl    -32(%rbp), %edx
    movl    %edx, %ecx
    subl    %eax, %ecx
    movl    %ecx, %eax
    movl    %eax, -24(%rbp)
    movl    $.LC0, %eax
    movl    -24(%rbp), %ecx
    movl    -28(%rbp), %edx
    movl    -32(%rbp), %ebx
    .cfi_offset 3, -24
    movl    %ebx, %esi
    movq    %rax, %rdi
    movl    $0, %eax
    call    printf
    movl    %eax, -20(%rbp)
    movl    -24(%rbp), %eax
    addq    $24, %rsp
    popq    %rbx
    leave
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE0:
    .size   main, .-main
    .ident  "GCC: (GNU) 4.4.6 20120305 (Red Hat 4.4.6-4)"
    .section    .note.GNU-stack,"",@progbits

Several things don't make sense:

(1) Why are we pushing %rbx? What is in %rbx that needs to be saved?

(2) Why are we moving %edx to %ecx before subtracting? What doesn't it just do sub %eax, %edx?

(3) Similarly, why the move from %ecx back to %eax before storing the va

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