Efficiency of Short Hand Notation

Why x += 1 ; is more efficient than x = x+1 ?

It is related to how assembler references the memory location accesss .
The ALU uses registers for referencing values and accumulator for storing partial results .
 So , for case 1 : 
  x =  x + 1 ;
 
  MOV A , (x) ;  // Move the value at memory location x in accumultor A  . The value of x is stored in register
  ADD A , 1  ; // ADD 1 IN ACCUMULATor
  MOV (X) ,  A ; // Move the value in accumulator at memory location referenced by x
 
  for case 2 :
  x += 1
  ADD (x) , 1 ; // Add 1 at memory location referenced by x
 
  So , so coz of efficient dereferncing and no partial result generation  , short hand artihmatic noations are efficient even though at an abstract view all operations produce same results