[llvm-dev] Old SimplifyInstruction API about to fully die

[Daniel Berlin via llvm-dev]

This is about to be done, as i have converted remaining users and the
bootstraps are just about done.
I will follow up with the rev number.

For those needing to convert out of tree uses:

Trivially, you should be able to take any place that has
SimplifyInstruction(I, ...), and do SimplifyInstruction(I, {...}).

However, where possible, it is going to be better to construct a
SimplifyQuery once and use it everywhere.
CorrelatedValuePropagation and LoopRotation have examples of how to do this.

I have converted everywhere where it is  easy to do so.to construct them
once, and everywhere else now constructs them using the above.

I am also introducing a helper function, named "getBestSimplifyQuery", that
can take Pass/AnalysisManager/LoopStandardAnalysis, and will construct the
best SimplifyQuery possible from whatever optional analysis are available.

Thus, in a Pass runOnFunction, you could do

const SimplifyQuery SQ = getBestSimplifyQuery(*this, F)

and it will hand you back a structure filled in with as many of the
analyses as are around and up to date. You can then pass that to
SimplifyInstruction later.

Using  this is strongly preferred as it will enable us to add analysis to
SimplifyInstruction and just update those functions.

I bootstrapped with every target enabled, sorry if i missed something!

On Wed, Apr 26, 2017 at 4:55 PM, Philip Reames via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Agreed.  This seems like overall a huge win for readability.
>
> I am a bit worried about all the miscompiles you're going to expose by
> using all that extra information, but we should definitely just fix those.
> :)
>
> Philip
>
> On 04/26/2017 08:53 AM, Hal Finkel via llvm-dev wrote:
>
>
> On 04/25/2017 11:32 PM, Daniel Berlin via llvm-dev wrote:
>
> For those not following along, startingin r301379, Simplify* in
> InstructionSimplify now can just take a query struct  instead of 8000
> optional arguments.  Nothing is really new since it used the same thing
> under the covers.
>
> I'm slowly converting the old uses away (deletion of the old APIs is a
> different question).
> Staring at most of them, i could just directly convert them using braced
> list initialization, and construct the objects again and again, but the
> vast majority of uses actually:
>
> A. don't change the relevant query arguments over the lifetime of the pass
> B. actually have more information sitting around than they are passing
> along.
>
> For example, instcombine has a DomTree and AssumptionCache that are
> required, but it doesn't pass them to SimplifyBinOp in a bunch of cases.
>
> JumpThreading has TLI but doesn't pass it to SimplifyCmpInst.
>
> CVP at least admits it has a problem:
> "CorrelatedValuePropagation.cpp:  // FIXME: Provide TLI, DT, AT to
> SimplifyInstruction.
> CorrelatedValuePropagation.cpp:  if (Value *V = SimplifyInstruction(P,
> DL)) {
> "
> (This is because it uses LVI, which requires those things, but it doesn't
> ask for them itself)
>
> Assuming this is not deliberate, it would seem to me to just be easiest to
> set up the query structure once in the pass and use it everywhere, which
> would hopefully avoid these issues in the future, besides making most of
> the call strings dramatically shorter :)
>
> Is there any real downside (compile time performance, etc) to this vs what
> we do now (which is basically constructing the query objects again and
> again under the covers) that anyone can think of?
>
> (again, assuming we are not deliberately avoiding passing info to
> Simplify* in most of these cases)
>
>
> I don't think it is deliberate; it is just that no one has done the work
> to make it uniform. It is possible that doing this will expose some
> compile-time issues, but if so, we should deal with them for real (not just
> hide them by a failure to provide optional-but-available analyses).
>
> I'm certainly in favor of more uniformity here.
>
>  -Hal
>
>
> I figured i'd ask before i went writing the scripts/etc to help convert a
> bunch of this stuff :)
>
>
>
> _______________________________________________
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>
>
> --
> Hal Finkel
> Lead, Compiler Technology and Programming Languages
> Leadership Computing Facility
> Argonne National Laboratory
>
>
>
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