[PATCH] D47023: Limit the number of phis in intptr/ptrint folding

[Xinliang David Li via llvm-commits]

This might work and existing test cases should be able to make sure the
behavior is not regressed.

David

On Fri, May 18, 2018 at 5:49 PM Michael Zolotukhin via Phabricator <
reviews at reviews.llvm.org> wrote:

> mzolotukhin added a comment.
>
> I thought about this transformation more, and I no longer think that we
> even need to move it to aggressive-instcombine (or another FunctionPass).
> What we need is to just change it from top-down to bottom-up: i.e. to start
> looking not from phi-nodes, but rather from `inttoptr` instructions. That
> is, the algorithm would look like:
>
>   visitIntToPtr(Instruction &I) {
>     Value *Def = I.getOperand()
>     if (!Def.hasSingleUse())
>        return;
>     if (isa<PtrToInt>(Def)) {   // Simple case without phi - it's probably
> already handled somewhere else, but I'm putting it here for completeness
>        I.replaceAllUsesWith(Def.getOperand());
>     }
>     if (isa<PHINode>(Def)) {    // Interesting case where we have a
> phi-node
>        if (all operands are PtrToInt with a single use) {
>          NewPHI = RewritePHI();
>          I.replaceAllUsesWith(NewPHI);
>       }
>     }
>   }
>
> What do you think? Would it work?
>
> PS: Internally we worked around the slowdown, so it's not pressing on us
> anymore.
>
> Michael
>
>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D47023
>
>
>
>
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