Single assignment

Single assignment is an optimization technique that breaks the connection between variable names in a high level programming language and their location in the assembler code.

The basic principle of single assigment is that each location is written only once. After that the location can only be read from.

Demonstration:

a:=x+y; b:=a-1; a:=y+b; b:=x*4; a:=a+b;

...becomes...

loc1:=x+y; loc2:=loc1-1; loc3:=y+loc2; loc4:=x*4; loc5:=loc3+loc4;