Re: rearranging code invalidates liveness info

Fergus Henderson <fjh@munta.cs.mu.OZ.AU> asks:
> anything but the most trivial rearrangements will invalidate the annotations
> on the code. ... How do compiler writers usually handle this problem?


mernst@research.microsoft.com writes:
>As others have pointed out, the traditional approaches are to either rerun
>all analyses after each transformation or to run analyses immediately
>before they are needed. At the other end of the spectrum (requiring much
>more work and potentially saving more effort) is incremental maintenance of
>semantic information, either directly or by rerunning analyses over a small
>affected region in which the semantic information has been invalidated.


You might try separating transformations which invalidate liveness
from those which don't. I have found the study of transformations
which don't affect liveness to be particularly interesting, because
they tend not to copy or destroy information. They also tend not to
affect synchronization in a multi-threaded world.


Unfortunately, I don't have much to report at this stage, so I am
working mainly on intuition.
--

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