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

[Craig Topper via llvm-commits]

But the contents of the second iteration of the worklist could be very
different based on what was skipped and what other changes happened in the
first iteration.

~Craig

On Tue, Mar 21, 2017 at 5:11 PM, Daniel Berlin <dberlin at dberlin.org> wrote:

>
>
> 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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>
>
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