If you have a single-pass compiler (for speed) then it will not know on pass #2 that the old value is to be used for something or not and can drop it. In a sin

If you have a single-pass compiler (for speed) then it will not know on pass #2 that the old value is to be used for something or not and can drop it. In a single-pass run, you must generate code to keep the previous value in case the line actually was foo = ++a; or foo = a++; so that foo gets the pre-inc or post-inc value. The small part that creates the code for the small "a++" part of the line will then produce a dead store of the pre-inc value, and no 2nd pass will remove it.