[LLVMdev] DominatorTree not updated properly after calling the llvm::SplitBlock.

[Paul Vario]

Hi Andrew,

     Thanks a lot. But the function "DT->dominate(A,B)" decides the
dominance relationship through comparing the DFS numbers, right? At least,
in my example, when I check whether the newly split node (i.e., %
*for.end.split*) DOMINATES the original node (I.e., %for.end), the answer
is true, which is obviously wrong.

Paul


On Fri, Feb 14, 2014 at 1:59 AM, Andrew Trick <atrick at apple.com> wrote:

>
> On Feb 13, 2014, at 4:34 PM, Paul Vario <paul.paul.mit at gmail.com> wrote:
>
> Hi Fellows,
>
>       I am writing a pass that requires the DominatorTree pass. In the
> runOnFunction of my own pass, I call llvm::SplitBlock to split a block
> (%for.end) at it's first insert point. Then, when I dump my dominator tree
> immediately after, I can see the newly split %for.end.split, but its
> DFSNumIn and DFSNumOut are not properly updated in llvm::SplitBlock (i.e.,
> still the initialized -1). At the same time, the DT->dump() results also
> show that DFSInfoValid equals false! I could not figure out what I did
> wrong, b/c it seems all the analysis updating should be handled by
> llvm::SplitBlock. Any suggestions on how to approach this situation? Thanks
> a bunch in advance.
>
>
> Hi Paul,
>
> DFSNumbers is a cache within the DominatorTree analysis. It is lazily
> computed after a certain number of queries. It's kind of hard to
> incrementally update these numbers because we may have to shift them all.
>
> At any rate, invalid DFS numbers does not mean something is wrong with the
> analysis.
>
> -Andy
>
>
>
> -------------------------  The actual dump of my dominator tree after
> SplitBlock --------------------
>
> Inorder Dominator Tree: DFSNumbers invalid: 1 slow queries.
>   [1] %entry.barrier {0,27}
>     [2] %entry {1,26}
>       [3] %for.cond {2,25}
>         [4] %for.body {3,6}
>           [5] %for.inc {4,5}
>         [4] %for.end {7,24}
>           *[5] %for.end.split {4294967295,4294967295}*
>             [6] %if.then {8,15}
>               [7] %if.then13 {9,10}
>               [7] %if.end {11,12}
>               [7] %if.then.if.end_crit_edge {13,14}
>             [6] %if.end14 {16,21}
>               [7] %exit.b4.barrier {17,20}
>                 [8] %exit.barrier {18,19}
>             [6] %for.end.if.end14_crit_edge {22,23}
>
>  _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20140214/682f2d71/attachment.html>