3 ms·

Why? You'd just keep the code in SSA and diff whenever the user adds code - you need to create the form _once_ but after you've created it diffing it should be

by inglor 11y ago

Why? You'd just keep the code in SSA and diff whenever the user adds code - you need to create the form _once_ but after you've created it diffing it should be reasonably fast - the creation can be done at project creation time and it can be changed on-line and incrementally. I'm not sure if tools actually do it but it definitely sounds possible.

danbruc 11y ago
How would maintaining a SSA representation of the code help detecting dead code paths? Doing so requires reasoning about possible truth values of conditions and is in general equivalent to the halting problem and therefore undecidable. You could only spend the cycles available in real time and that will in a certain number of cases be enough to solve the problem but there will also be instances requiring more cycles and instances being undecidable.
- inglor 11y ago
  > How would maintaining a SSA representation of the code help detecting dead code paths? Well, if a variable assigned but never appears in a path that might have side effects it's dead. It's only the halting problem if you pretend to catch 100% of cases under all inputs. You can find lots of dead code without it. For more information about the specific technique of DCE under SSA form see http://grothoff.org/christian/teaching/2007/3353/papers/ssa.pdf http://grothoff.org/christian/teaching/2007/3353/papers/ssa....
- seanmcdirmid 11y ago
  Going incremental is another option: if the analysis was done overnight and you only made a few changes, there shouldn't be much to do to "repair" the analysis according to your changes. But the PL community is not really good with incremental computations, especially ones that must consider arbitrary code changes (which, for example, can cause non-monotonic movements in your lattices).
  - dllthomas 11y ago
    '[I]f the analysis was done overnight and you only made a few changes, there shouldn't be much to do to "repair" the analysis according to your changes.' I would be tremendously surprised if that proved to be true in the general case, but it might well be true enough in common cases to be practical. Very interesting notion...
  - deleted 11y ago
    [deleted]

by inglor 11y ago

danbruc 11y ago

How would maintaining a SSA representation of the code help detecting dead code paths? Doing so requires reasoning about possible truth values of conditions and is in general equivalent to the halting problem and therefore undecidable. You could only spend the cycles available in real time and that will in a certain number of cases be enough to solve the problem but there will also be instances requiring more cycles and instances being undecidable.

inglor 11y ago
> How would maintaining a SSA representation of the code help detecting dead code paths? Well, if a variable assigned but never appears in a path that might have side effects it's dead. It's only the halting problem if you pretend to catch 100% of cases under all inputs. You can find lots of dead code without it. For more information about the specific technique of DCE under SSA form see http://grothoff.org/christian/teaching/2007/3353/papers/ssa.pdf http://grothoff.org/christian/teaching/2007/3353/papers/ssa....
seanmcdirmid 11y ago
Going incremental is another option: if the analysis was done overnight and you only made a few changes, there shouldn't be much to do to "repair" the analysis according to your changes. But the PL community is not really good with incremental computations, especially ones that must consider arbitrary code changes (which, for example, can cause non-monotonic movements in your lattices).
- dllthomas 11y ago
  '[I]f the analysis was done overnight and you only made a few changes, there shouldn't be much to do to "repair" the analysis according to your changes.' I would be tremendously surprised if that proved to be true in the general case, but it might well be true enough in common cases to be practical. Very interesting notion...
- deleted 11y ago
  [deleted]