Understanding exactly how the increased efficiency is achieved in Assembly language - c

Question

I have generated two assembly files - one that is optimized, and one that is not. The assembly-language code generated with optimization on should be more efficient than the other assembly-language code. I am more interested in how the efficiency is achieved. To my understanding, in the non-optimized version there will always have to be an offset call to the register %rbp to find the address. In the optimized version, the addresses are being stored in the registers, so you don't have to rely and call on %rbp to find them.
Am I correct? And if so, would there ever be a time when the optimized version will not be advantageous? Thank you for your time.
Here is a function that converts from 42 GIF to CYMK.
void rgb2cmyk(int r, int g, int b, int ret[]) {
int c = 255 - r;
int m = 255 - g;
int y = 255 - b;
int k = (c < m) ? (c < y ? c : y) : (m < y ? m : y);
c -= k; m -= k; y -= k;
ret[0] = c; ret[1] = m; ret[2] = y; ret[3] = k;
}
Here is the assembly-language code that has not been optimized. Note I have made notes using ;; in the code.
No Opt:
.section __TEXT,__text,regular,pure_instructions
.globl _rgb2cmyk
.align 4, 0x90
_rgb2cmyk: ## #rgb2cmyk
.cfi_startproc
## BB#0:
pushq %rbp
Ltmp2:
.cfi_def_cfa_offset 16
Ltmp3:
.cfi_offset %rbp, -16
movq %rsp, %rbp
Ltmp4:
.cfi_def_cfa_register %rbp
;;initializing variable c, m, y
movl $255, %eax
movl %edi, -4(%rbp)
movl %esi, -8(%rbp)
movl %edx, -12(%rbp)
movq %rcx, -24(%rbp)
movl %eax, %edx
subl -4(%rbp), %edx
movl %edx, -28(%rbp)
movl %eax, %edx
subl -8(%rbp), %edx
movl %edx, -32(%rbp)
subl -12(%rbp), %eax
movl %eax, -36(%rbp)
movl -28(%rbp), %eax
;;compare
cmpl -32(%rbp), %eax
jge LBB0_5
## BB#1:
movl -28(%rbp), %eax
cmpl -36(%rbp), %eax
jge LBB0_3
## BB#2:
movl -28(%rbp), %eax
movl %eax, -44(%rbp) ## 4-byte Spill
jmp LBB0_4
LBB0_3:
movl -36(%rbp), %eax
movl %eax, -44(%rbp) ## 4-byte Spill
LBB0_4:
movl -44(%rbp), %eax ## 4-byte Reload
movl %eax, -48(%rbp) ## 4-byte Spill
jmp LBB0_9
LBB0_5:
movl -32(%rbp), %eax
cmpl -36(%rbp), %eax
jge LBB0_7
## BB#6:
movl -32(%rbp), %eax
movl %eax, -52(%rbp) ## 4-byte Spill
jmp LBB0_8
LBB0_7:
movl -36(%rbp), %eax
movl %eax, -52(%rbp) ## 4-byte Spill
LBB0_8:
movl -52(%rbp), %eax ## 4-byte Reload
movl %eax, -48(%rbp) ## 4-byte Spill
LBB0_9:
movl -48(%rbp), %eax ## 4-byte Reload
movl %eax, -40(%rbp)
movl -40(%rbp), %eax
movl -28(%rbp), %ecx
subl %eax, %ecx
movl %ecx, -28(%rbp)
movl -40(%rbp), %eax
movl -32(%rbp), %ecx
subl %eax, %ecx
movl %ecx, -32(%rbp)
movl -40(%rbp), %eax
movl -36(%rbp), %ecx
subl %eax, %ecx
movl %ecx, -36(%rbp)
movl -28(%rbp), %eax
movq -24(%rbp), %rdx
movl %eax, (%rdx)
movl -32(%rbp), %eax
movq -24(%rbp), %rdx
movl %eax, 4(%rdx)
movl -36(%rbp), %eax
movq -24(%rbp), %rdx
movl %eax, 8(%rdx)
movl -40(%rbp), %eax
movq -24(%rbp), %rdx
movl %eax, 12(%rdx)
popq %rbp
retq
.cfi_endproc
.subsections_via_symbols
Optimization:
.section __TEXT,__text,regular,pure_instructions
.globl _rgb2cmyk
.align 4, 0x90
_rgb2cmyk: ## #rgb2cmyk
.cfi_startproc
## BB#0:
pushq %rbp
Ltmp2:
.cfi_def_cfa_offset 16
Ltmp3:
.cfi_offset %rbp, -16
movq %rsp, %rbp
Ltmp4:
.cfi_def_cfa_register %rbp
movl $255, %r8d
movl $255, %eax
subl %edi, %eax
movl $255, %edi
subl %esi, %edi
subl %edx, %r8d
cmpl %edi, %eax ##;; compare m and c
jge LBB0_2
## BB#1: ;; c < m
cmpl %r8d, %eax ## compare y and c
movl %r8d, %edx
cmovlel %eax, %edx
jmp LBB0_3
LBB0_2: ##;; c >= m
cmpl %r8d, %edi ## compare y and m
movl %r8d, %edx
cmovlel %edi, %edx
LBB0_3:
subl %edx, %eax
subl %edx, %edi
subl %edx, %r8d
movl %eax, (%rcx)
movl %edi, 4(%rcx)
movl %r8d, 8(%rcx)
movl %edx, 12(%rcx)
popq %rbp
retq
.cfi_endproc
.subsections_via_symbols

Answer 1

Yes. The optimized version performs many fewer memory read operations by storing intermediate values in registers and not reloading them over and over.
You are using call wrong. It is a technical term that means to push a return address on the stack and branch to a new location for instructions. The term you mean is simply to use the register.
Can you think of a reason that longer, slower code is "better"?