[PATCH] D31120: [InstCombine] Teach SimplifyDemandedUseBits that adding or subtractings 0s from every bit below the highest demanded bit can be simplified

[Daniel Berlin via llvm-commits]

On Tue, Mar 21, 2017 at 4:52 PM, Craig Topper via Phabricator via
llvm-commits <llvm-commits at lists.llvm.org> wrote:

> craig.topper added a comment.
>
> Yeah I saw that. Should we add a debug counter around the top level
> worklist loop? The semantics of the "skip" part of the counter wouldn't
> make sense though.
>
> That depends on what semantics you want out of it :)

FWIW: In NewGVN, we want the semantic of the value numbering counter to to
be "choose which  instructions are processed on each iteration of the
worklist".

There are two ways to accomplish that:
1. Record which were skipped, skip them again (some cost)
or
2. use the isCounterSet/etc to reset the counter at the start of  each
iteration of the worklist to the same values. (no cost if debug is off,
though i see i forgot to make this constant when #ifdef NDEBUG)


> https://reviews.llvm.org/D31120
>
>
>
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