assembly leal and movl difference [duplicate]

Question

This question already has an answer here:

• Using LEA on values that aren't addresses / pointers? 3 answers

leal(%eax,%ecx,4), %edx

as I was reading from my computer systems book, if there`s premises that $eax contains x value and %ecx contains y, then the above means, x+4y putting into %edx.

then if it is

movl(%eax,%ecx,4), %edx

, then isn`t the same one with leal expression above?

As I know, leal creates address that can be referenced,not referencing by itself like movl, but

when I saw leal(%eax,%ecx,4), %edx equals putting x+4y into edx register, then doesnt it mean that it 'referenced'%eaxand%ecx` and extracted value x and y for using computation??

• doesn`t it "()" means 'referenced'??

Answer 1

LEA loads an effective address generated by an address calculation into a register. MOV moves something somewhere, when using SIB addressing as source operand, it moves whatever is at the address generated by the address calculation into the target operand.

So:

leal (%eax,%ecx,4), %edx  ←  moves %eax+%ecx*4 into %edx
movl (%eax,%ecx,4), %edx  ←  moves whatever is at address %eax+%ecx*4 into %edx