How to identify a loop on the instruction level?

Asked Jun 06 '13 at 19:54

Active Jun 06 '13 at 20:22

Viewed 109 times

Can a direct branch instruction with a lower target address than the address of the branch instruction itself be considered as the beginning of a loop? Is this condition sufficient, or are there are other situations (compiler optimizations, etc) in which similar behaviour is shown on the instruction level.

What other approach would you recommend? The obvious one is storing a list of target addresses encountered and if a target address is taken by the same instruction more than once, it means it's the beginning of a loop. The downside of that is that it takes up memory of storing all the addresses and time for checks.

asked Jun 06 '13 at 19:54

lekroif

The branch can be considered the end of a loop. And it isn't sufficient, you can always use goto in c and jump somewhere. – tomato Jun 06 '13 at 20:01
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And this is ignoring stuff like delay slots and other optimisations. – tomato Jun 06 '13 at 20:03
yes, I realize the idea about ignoring gotos – lekroif Jun 06 '13 at 20:07
@tomato what other optimisations? – lekroif Jun 06 '13 at 20:07
Loop fission / Fusion , unswitching, and others – tomato Jun 06 '13 at 20:41
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define loop...are you talking about high level language loops or loops at the instruction level? Instruction is pretty obvious, high level you wont find a foolproof way to figure it out, not worth the effort. – old_timer Jun 07 '13 at 00:39

How to identify a loop on the instruction level?

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