x = x + 2

# Load x and 2
mov -16(%rbp), %rax
mov $2, %rbx
# Perform addition, i.e., rax = rax + rbx
add %rbx, %rax
# Store result in x
mov %rax, -16(%rbp)

int main(int argc, char **argv) {
  int x;
  int retval;
  x = read_int();
  x *= 2;
  retval = print_int(x);
  return 0;
}

begin main(argc, argv)
locals x, retval
x = read_int()
x = x * 2
retval = print_int(x)
return 0
end

begin main()
return 0
end

begin main(argc, argv)
locals x, y
# Instructions go here
return 0
end

x = 2
y = x

x = x + 2

x = print_int(x)

if x > 0 goto endlabel
x = x * -1
endlabel:

t1 = &x
t2 = *t1
*t1 = 11

begin exponent(base, exp)
locals result
result = 1
top:
if exp <= 0 goto endlabel
result = result * base
exp = exp - 1
goto top
endlabel:
return result
end

program     =   function
function    =   'begin' identifier parameters newlines [ locals ] body 'end' newlines
ident       =   ?a-zA-Z_?{ ?a-zA-Z1-9_? }
parameters  =   '(' [ identifiers ] ')'
identifiers =   identifier { ',' identifier }
locals      =   'locals' identifiers newlines
body        =   { statement newlines } return newlines
return      =   'return' value
newlines    =   '\n' { '\n' }

statement   =   assignment
                | arithmetic 
                | call
                | label
                | goto
                | if
                | reference
                | assignment_dereference
                | dereference_assignment
assignment  =   identifier '=' value
value       =   identifier | integer
identifier  =   ? An alphanumeric sequence possibly containing '_' and not
                  starting with a number ?
integer     =   ? A sequence of integers not starting with zero ?
arithmetic  =   identifier '=' value arithop value
arithop     =   '+' | '-' | '*' | '/' | '%'
call        =   identifier '=' identifier '(' arguments ')'
arguments   =   [ argument { ',' argument } ]
argument    =   value
label       =   identifier ':'
goto        =   'goto' identifier
if          =   'if' value relational_operator value 'goto' identifier

relational_operator     =   '<' | '>' | '=' | '<=' | '>=' | '!='
reference               =   identifier '=' '&' identifier
assignment_dereference  =   identifier '=' '*' identifier
dereference_assignment  =   '*' identifier '=' value

begin main()
locals x y
x = 3
y = 5
return 0
end

locals x, y

x = 3

# Assign 3 to x
mov $3, %rax
mov %rax, -16(%rbp)

-16(%rbp)   # rbp[-16]

.file "stdin"
.section .note.GNU-stack,"",@progbits
.text
.globl main
.type main, @function
main:
    # Prologue, update stack pointer
    pushq   %rbp        # Save old base ponter
    movq    %rsp, %rbp  # Set new base pointer
    push    %rbx        # %rbx is callee-saved
    sub $24, %rsp       # Allocate stack space for locals

    # Assign 3 to x
    mov $3, %rax
    mov %rax, -16(%rbp)

    # Assign 5 to y
    mov $5, %rax
    mov %rax, -24(%rbp)

    # Set return value
    mov $0, %rax

    # Epilogue
    add $24, %rsp       # Deallocate space for locals
    pop %rbx            # Restore %rbx
    pop %rbp            # Restore old base pointer
    ret                 # Return