[LLVMdev] Updating PHI for Instruction Domination?

Eric Christopher echristo at apple.com
Thu Feb 2 17:05:07 PST 2012

Not that I'm aware of.


On Feb 2, 2012, at 3:47 PM, Ryan Taylor wrote:

> So essentially I'm adding a path inside of the loop. Is there a way to have llvm automatically create new IR and update the PHIs simply by adding a block like this and changing the DomTree?
> ---------- Forwarded message ----------
> From: Ryan Taylor <ryta1203 at gmail.com>
> Date: Thu, Feb 2, 2012 at 12:08 PM
> Subject: Updating PHI for Instruction Domination?
> To: llvmdev at cs.uiuc.edu
> So I have a loop with two blocks, a header (which points to return and latch) and a latch (which points to return and header). I have inserted a few new blocks, called H and F. 
> Header now points to H and latch. Latch now points to F. H points to F. F points to Header and return.
> The PHI Nodes have been updated in Header accordingly, now coming from the preheader and F (instead of latch).
> My issue is this: The values in the PHI instruction in the Header for F are actually defined in Latch and so if you follow the path: Header->H->F, there becomes an issue with "Instruction does not dominate all uses" (since the Header PHI is getting values defined in Latch coming from F but never going to Latch) since they haven't been defined in that path.
> My question is: Is there some call where I can rearrange the basic blocks and call some functions/utils that solve this issue? Or do I have to manually solve this myself?
> Thanks again.
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