[LLVMbugs] [Bug 217] NEW: LLVM needs a generic dominator update mechanism

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=217

           Summary: LLVM needs a generic dominator update mechanism
           Product: libraries
           Version: trunk
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Global Analyses
        AssignedTo: sabre at nondot.org
        ReportedBy: sabre at nondot.org


Certain transformations, like tail-duplication (Bug 174) and the correlated
expression elimination pass, fundamentally need to make arbitrary changes to the
CFG _AND_ update the SSA form of expressions.  To do this, they need to _update_
dominators and dominator frontiers as they change the CFG.

Basically the dominator information passes need an 'addEdge/removeEdge'
interface that clients can use to incrementally update the dominator
information.  There is a paper that describes how to do this:

http://citeseer.nj.nec.com/sreedhar94efficient.html

... someone should implement it.

Given this functionality, many other transformations would also be able to
incrementally update dominator information, instead of recalculating it, which
would speed up the optimizer as well.

-Chris



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