From: Jim PlankDate: Tue, 7 Oct 1997 13:31:42 -0400 To: cs360 class Here is a question that I just answered. I figure perhaps you all might like to see it in case you are having similar questions: > > When I do: > st %r0 -> [fp] > > will the %r0 be freed after this ? No, it doesn't get "freed". It is a register, and will hold its value until that value is altered. > In your example, you have many things like (f.g. the second > example of Assembler Lecture #2): > > st %r0 -> [fp] > ld [fp] -> %r0 > > It seems to me this is redundant if %r0 is not freed. Absolutely it is redundant. However, compilers produce code like this because they convert C into assembler in a line by line bases. When they optimize, they can get rid of redundancies like that. > Now let's say I have a segment of C like: > i=10; > j=10; > > Do I need to transform them into: > mv #10 -> %r0 > st %r0 -> [fp] > > mv #10 -> %r0 > st %r0 -> [fp-4] Yes > or just > > mv #10 -> %r0 > st %r0 -> [fp] > st %r0 -> [fp-4] > ? > > Do you think for the latter case, I did optimization ? In the latter case, you did optimization. -- Jim Plank Assistant Professor, Computer Science plank@cs.utk.edu University of Tennessee http://web.eecs.utk.edu/~jplank 107 Ayres Hall office: 423-974-4397, fax: 423-974-4404 Knoxville, TN 37996