[llvm-dev] [PM] I think that the new PM needs to learn about inter-analysis dependencies...

[Hal Finkel via llvm-dev]

----- Original Message -----

> From: "Sean Silva" <chisophugis at gmail.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: "Xinliang David Li" <davidxl at google.com>, "llvm-dev"
> <llvm-dev at lists.llvm.org>, "Davide Italiano"
> <dccitaliano at gmail.com>, "Tim Amini Golling"
> <mehdi.amini at apple.com>, "Sanjoy Das"
> <sanjoy at playingwithpointers.com>, "Pete Cooper"
> <peter_cooper at apple.com>, "Chandler Carruth" <chandlerc at gmail.com>
> Sent: Monday, July 25, 2016 2:47:19 PM
> Subject: Re: [PM] I think that the new PM needs to learn about
> inter-analysis dependencies...

> On Mon, Jul 25, 2016 at 9:27 AM, Hal Finkel < hfinkel at anl.gov >
> wrote:

> > > From: "Sean Silva" < chisophugis at gmail.com >
> > 
> 
> > > To: "Chandler Carruth" < chandlerc at gmail.com >
> > 
> 
> > > Cc: "Xinliang David Li" < davidxl at google.com >, "llvm-dev" <
> > > llvm-dev at lists.llvm.org >, "Davide Italiano" <
> > > dccitaliano at gmail.com
> > > >, "Tim Amini Golling" < mehdi.amini at apple.com >, "Hal Finkel" <
> > > hfinkel at anl.gov >, "Sanjoy Das" < sanjoy at playingwithpointers.com
> > > >,
> > > "Pete Cooper" < peter_cooper at apple.com >
> > 
> 
> > > Sent: Thursday, July 21, 2016 3:59:28 AM
> > 
> 
> > > Subject: Re: [PM] I think that the new PM needs to learn about
> > > inter-analysis dependencies...
> > 
> 

> > > We did some basic sanity checking that memory usage didn't go out
> > > of
> > > control (it doesn't; at least with with a simple
> > > preserves-all/preserves-none invalidation scheme and the current
> > > LTO
> > > pipeline). Also, I did some basic sanity checking for compile
> > > time.
> > > The simple preserves-all/preserves-none invalidation scheme seems
> > > marginally slower, but no real conclusions (besides a simple
> > > sanity
> > > check) can be drawn without the real analysis preservation
> > > semantics
> > > in place.
> > 
> 

> > > I'll start working on fixing the analysis managers. There seem to
> > > basically be two parts (although they may need to be done
> > > simultaneously to make sure all the pieces fit together):
> > 
> 
> > > - unify all the analysis managers into a single analysis manager
> > > for
> > > all IRUnitT's (requires type-erasing the IRUnit)
> > 
> 
> > > - introduce the dependency tracking machinery
> > 
> 

> > > I think I gave a reasonable outline in the two posts above:
> > 
> 
> > > - the one starting with " To clarify, it seems like the current
> > > new
> > > PM is essentially trying to solve the problem of
> > > maintaining/updating a mapping"
> > 
> 
> > > - the one starting with " Yeah, the mechanics of maintaining this
> > > fully general mapping are straightforward in the abstract"
> > 
> 

> > > I'm happy to do a centralized writeup if anybody wants. Just let
> > > me
> > > know.
> > 
> 

> > > As far as changes to the code, t he updates to the new PM passes
> > > should hopefully be mechanical (despite there being many of
> > > them).
> > > However, from what I can tell, fixing this problem will require
> > > touching most lines of the analysis manager machinery so the diff
> > > will probably be a bit scary, even though I think we can keep the
> > > same basic structure (i.e. a per-IRUnit std::list holding one
> > > analysis result (at a stable address) per element, combined with
> > > a
> > > DenseMap from (Analysis, IRUnit) to an element of the per-IRUnit
> > > storage list (see AnalysisResultListMapT and AnalysisResultMapT
> > > in
> > > include/llvm/IR/PassManager.h)).
> > 
> 
> > > The main changes to the analysis manager will be:
> > 
> 
> > > - type-erasing the IRUnit
> > 
> 
> > > - the elements of the AnalysisResultListMapT will need to keep
> > > track
> > > of any dependents
> > 
> 
> > > - the analysis manager will need to update those dependencies as
> > > it
> > > is re-entered by analyses getting results of other analyses
> > 
> 
> > > - the analysis manager will need to walk the dependencies to do
> > > transitive invalidation
> > 
> 

> > > I think the most robust approach is for analysis dependencies to
> > > be
> > > implicitly constructed by the analysis manager via tracking
> > > entry/exit from get{,Cached}Result.
> > 
> 
> > > One alternative is for analyses to explicitly pass in their ID to
> > > getResult to indicate the dependency, but that seems error-prone
> > > (and also verbose). The issue is that we will need a getResult
> > > API
> > > that does not track dependencies for use by transformation passes
> > > (since there is no dependency to track in that case); so an
> > > innocuous copy-paste from a transform pass to an analysis can
> > > result
> > > in a failure to track dependencies and risk of use-after-free (we
> > > could fight this with the type system, but I think that would get
> > > a
> > > bit verbose (I'm willing to try it though if people would
> > > prefer))
> > 
> 
> > > One restriction of the implicit tracking approach is that it
> > > requires
> > > all calls into the analysis manager to occur in the `run` method
> > > of
> > > the analysis (so that the dependencies are implicitly tracked via
> > > re-entrance to get{,Cached}Result); is this a reasonable
> > > restriction?
> > 
> 

> > What's the potential use case for getting an analysis outside of
> > something in, or called by, run()?
> 
> The main thing I had in mind was that if an analysis happens to stash
> a pointer directly to the analysis manager, then it may call into
> the analysis manager in the query path. For example, you would have
> this situation if a module analysis has a query path that wants to
> lazily compute a function analysis (i.e. compute the function
> analysis outside of the `run` call).
Yes, I'm pretty sure that we want to support that (a module analysis lazily getting function-level analysis results on the functions in the module). To put it another way, we definitely want a module transformation to be able to do that, and if an analysis can't, that limits our ability to properly organize/reuse code. 

We might have a slightly different interface for that, however, if it can't be implicit in that case. 

-Hal 

> > > One annoying problem is that I think that the dependency links
> > > will
> > > need to be bidirectional. To use the example analysis cache from
> > > my
> > > other post:
> > 
> 

> > > (AssumptionAnalysis, function @bar) -> (AssumptionCache for @bar,
> > > [(SomeModuleAnalysis, module TheModule)])
> > 
> 
> > > (AssumptionAnalysis, function @baz) -> (AssumptionCache for @baz,
> > > [(SomeModuleAnalysis, module TheModule)])
> > 
> 
> > > (SomeModuleAnalysis, module TheModule) ->
> > > (SomeModuleAnalysisResult
> > > for TheModule, [(SomeFunctionAnalysis, function @baz)])
> > 
> 
> > > (SomeFunctionAnalysis, function @baz) ->
> > > (SomeFunctionAnalysisResult
> > > for @baz, [])
> > 
> 

> > > if we delete function @baz, then the dependent list
> > > [(SomeFunctionAnalysis, function @baz)] for `
> > > (SomeModuleAnalysis,
> > > module TheModule)` will now have a stale pointer to function
> > > @baz.
> > > I
> > > think that in practice we can check to see if `
> > > (SomeFunctionAnalysis, function @baz)` is in our hash table and
> > > if
> > > it isn't then just ignore the dependency as "this dependent
> > > analysis
> > > result has already been freed". In the worst case (memory
> > > allocator
> > > reuses the memory for another function) we may spuriously free an
> > > analysis result for a different function. However it is still
> > > unsettling (and may actually be UB in C++?).
> > 
> 
> > > Ideally we would track bidirectional links; that way when we
> > > remove
> > > an analysis result we also have it remove itself from dependence
> > > lists of all of its dependencies.
> > 
> 

> > I think that bidirectional tracking is preferable. I don't see how
> > to
> > avoid UB otherwise, and spuriously freeing things based on
> > allocator
> > address reuse will likely lead to non-deterministic behavior (e.g.
> > because a re-run analysis might be more accurate than a preserved
> > one).
> 

> Yeah, it doesn't seem onerous to maintain the bidirectional tracking
> (I have a design mocked up in my log). The problem actually ends up
> being similar to use/user tracking we have in the IR data structures
> (although it's different enough that there isn't really any code to
> share).

> -- Sean Silva

> > Thanks again,
> 
> > Hal
> 

> > > -- Sean Silva
> > 
> 

> > > On Fri, Jul 15, 2016 at 8:40 PM, Sean Silva <
> > > chisophugis at gmail.com
> > > >
> > > wrote:
> > 
> 

> > > > On Fri, Jul 15, 2016 at 8:39 PM, Sean Silva <
> > > > chisophugis at gmail.com
> > > > >
> > > > wrote:
> > > 
> > 
> 

> > > > > It looks like there is really no sane fix within the current
> > > > > infrastructure. I've had to essentially trigger invalidation
> > > > > (except
> > > > > in the PreservedAnalyses::all() case) in the function pass
> > > > > manager
> > > > > and function to loop adapters.
> > > > 
> > > 
> > 
> 
> > > > invalidation of *everything* I mean.
> > > 
> > 
> 

> > > > -- Sean Silva
> > > 
> > 
> 

> > > > > So we basically need to get the analysis manager dependency
> > > > > tracking
> > > > > fixed.
> > > > 
> > > 
> > 
> 

> > > > > Davide and I will get measurements on the resident set impact
> > > > > of
> > > > > all
> > > > > this caching (even with the overconservative invalidation for
> > > > > now)
> > > > > to see the impact. If there is a big rss impact then we
> > > > > probably
> > > > > want to consider that problem at the same time as the rewrite
> > > > > of
> > > > > the
> > > > > analysis manager.
> > > > 
> > > 
> > 
> 

> > > > > -- Sean Silva
> > > > 
> > > 
> > 
> 

> > > > > On Thu, Jul 14, 2016 at 12:51 AM, Sean Silva <
> > > > > chisophugis at gmail.com
> > > > > > wrote:
> > > > 
> > > 
> > 
> 

> > > > > > On Wed, Jul 13, 2016 at 1:48 AM, Sean Silva <
> > > > > > chisophugis at gmail.com
> > > > > > >
> > > > > > wrote:
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > On Wed, Jul 13, 2016 at 12:34 AM, Chandler Carruth <
> > > > > > > chandlerc at gmail.com > wrote:
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > On Wed, Jul 13, 2016 at 12:25 AM Sean Silva <
> > > > > > > > chisophugis at gmail.com
> > > > > > > > >
> > > > > > > > wrote:
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > On Tue, Jul 12, 2016 at 11:39 PM, Chandler Carruth <
> > > > > > > > > chandlerc at gmail.com > wrote:
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > > On Tue, Jul 12, 2016 at 11:34 PM Sean Silva <
> > > > > > > > > > chisophugis at gmail.com
> > > > > > > > > > >
> > > > > > > > > > wrote:
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > > > On Tue, Jul 12, 2016 at 11:32 PM, Xinliang David
> > > > > > > > > > > Li
> > > > > > > > > > > <
> > > > > > > > > > > davidxl at google.com > wrote:
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > > > > On Tue, Jul 12, 2016 at 10:57 PM, Chandler
> > > > > > > > > > > > Carruth
> > > > > > > > > > > > <
> > > > > > > > > > > > chandlerc at gmail.com > wrote:
> > > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > > > > > Yea, this is a nasty problem.
> > > > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > > > > > One important thing to understand is that
> > > > > > > > > > > > > this
> > > > > > > > > > > > > is
> > > > > > > > > > > > > specific
> > > > > > > > > > > > > to
> > > > > > > > > > > > > analyses which hold references to other
> > > > > > > > > > > > > analyses.
> > > > > > > > > > > > > While
> > > > > > > > > > > > > this
> > > > > > > > > > > > > isn't
> > > > > > > > > > > > > unheard of, it isn't as common as it could
> > > > > > > > > > > > > be.
> > > > > > > > > > > > > Still,
> > > > > > > > > > > > > definitely
> > > > > > > > > > > > > something we need to address.
> > > > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > > > > We can call this type of dependencies (holding
> > > > > > > > > > > > references)
> > > > > > > > > > > > hard-dependency. The soft dependency refers to
> > > > > > > > > > > > the
> > > > > > > > > > > > case
> > > > > > > > > > > > where
> > > > > > > > > > > > analysis 'A' depends on 'B' during computation,
> > > > > > > > > > > > but
> > > > > > > > > > > > does
> > > > > > > > > > > > not
> > > > > > > > > > > > need
> > > > > > > > > > > > 'B' once it is computed.
> > > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > > > > There are actually quite a few examples of
> > > > > > > > > > > > hard-dependency
> > > > > > > > > > > > case.
> > > > > > > > > > > > For
> > > > > > > > > > > > instance LoopAccessInfo, LazyValueInfo etc
> > > > > > > > > > > > which
> > > > > > > > > > > > hold
> > > > > > > > > > > > references
> > > > > > > > > > > > to
> > > > > > > > > > > > other analyses.
> > > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > > > > Problem involving hard-dependency is actually
> > > > > > > > > > > > easier
> > > > > > > > > > > > to
> > > > > > > > > > > > detect,
> > > > > > > > > > > > as
> > > > > > > > > > > > it
> > > > > > > > > > > > is usually a compile time problem. Issues
> > > > > > > > > > > > involving
> > > > > > > > > > > > soft
> > > > > > > > > > > > dependencies are more subtle and can lead to
> > > > > > > > > > > > wrong
> > > > > > > > > > > > code
> > > > > > > > > > > > gen.
> > > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > > > Did you mean to say that soft-dependency problems
> > > > > > > > > > > are
> > > > > > > > > > > easier
> > > > > > > > > > > to
> > > > > > > > > > > detect? At least my intuition is that
> > > > > > > > > > > soft-dependency
> > > > > > > > > > > is
> > > > > > > > > > > easier
> > > > > > > > > > > because there is no risk of dangling pointers to
> > > > > > > > > > > other
> > > > > > > > > > > analyses.
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > > The issue is that the fact that there is *any*
> > > > > > > > > > dependency
> > > > > > > > > > isn't
> > > > > > > > > > clear.
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > > However, I think the only real problem here are
> > > > > > > > > > these
> > > > > > > > > > "hard
> > > > > > > > > > dependencies" (I don't really like that term
> > > > > > > > > > though).
> > > > > > > > > > For
> > > > > > > > > > others,
> > > > > > > > > > only an analysis that is *explicitly* preserved
> > > > > > > > > > survives.
> > > > > > > > > > So
> > > > > > > > > > I'm
> > > > > > > > > > not
> > > > > > > > > > worried about the fact that people have to remember
> > > > > > > > > > this.
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > > The question is how often there are
> > > > > > > > > > cross-data-structure
> > > > > > > > > > references.
> > > > > > > > > > David mentions a few examples, and I'm sure there
> > > > > > > > > > are
> > > > > > > > > > more,
> > > > > > > > > > but
> > > > > > > > > > it
> > > > > > > > > > isn't clear to me yet whether this is pervasive or
> > > > > > > > > > occasional.
> > > > > > > > > 
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > I just did a quick run-through of PassRegistry.def
> > > > > > > > > and
> > > > > > > > > this
> > > > > > > > > is
> > > > > > > > > what
> > > > > > > > > I
> > > > > > > > > found:
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > Module analyses: 0/5 hold pointers to other analyses
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > CallGraph: No pointers to other analyses.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > LazyCallGraph: No pointers to other analyses.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > ProfileSummaryAnalysis: No pointers to other
> > > > > > > > > analyses.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > TargetLibraryAnalysis: No pointers to other analyses.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > VerifierAnalysis: No pointers to other analyses.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > Module alias analyses: 1/1 keeps pointer to other
> > > > > > > > > analysis.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > GlobalsAA: Result keeps pointer to TLI (this is a
> > > > > > > > > function
> > > > > > > > > analysis).
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > Function analyses: 9/17 keep pointers to other
> > > > > > > > > analysis
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > AAManager: Its Result holds TLI pointer and pointers
> > > > > > > > > to
> > > > > > > > > individual
> > > > > > > > > AA
> > > > > > > > > result objects.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > AssumptionAnalysis: No pointers to other analyses.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > BlockFrequencyAnalysis: Its Result holds pointers to
> > > > > > > > > LoopInfo
> > > > > > > > > and
> > > > > > > > > BPI.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > BranchProbabilityAnalysis: Stores no pointers to
> > > > > > > > > other
> > > > > > > > > analyses.
> > > > > > > > > (uses LoopInfo to "recalculate" though)
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > DominatorTreeAnalysis: Stores no pointers to other
> > > > > > > > > analyses.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > PostDominatorTreeAnalysis: Stores no pointers to
> > > > > > > > > other
> > > > > > > > > analyses.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > DemandedBitsAnalysis: Stores pointers to
> > > > > > > > > AssumptionCache
> > > > > > > > > and
> > > > > > > > > DominatorTree
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > DominanceFrontierAnalysis: Stores no pointers to
> > > > > > > > > other
> > > > > > > > > analyses.
> > > > > > > > > (uses DominatorTreeAnalysis for "recalculate"
> > > > > > > > > though).
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > LoopInfo: Uses DominatorTreeAnalysis for
> > > > > > > > > "recalculate"
> > > > > > > > > but
> > > > > > > > > stores
> > > > > > > > > no
> > > > > > > > > pointers.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > LazyValueAnalysis: Stores pointers to
> > > > > > > > > AssumptionCache,
> > > > > > > > > TargetLibraryInfo, DominatorTree.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > DependenceAnalysis: Stores pointers to AliasAnalysis,
> > > > > > > > > ScalarEvolution, LoopInfo
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > MemoryDependenceAnalysis: Stores pointers to
> > > > > > > > > AliasAnalysis,
> > > > > > > > > AssumptionCache, TargetLibraryInfo, DominatorTree
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > MemorySSAAnalysis: Stores pointers to AliasAnalysis,
> > > > > > > > > DominatorTree
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > RegionInfoAnalysis: Stores pointers to DomTree,
> > > > > > > > > PostDomTree,
> > > > > > > > > DomFrontier
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > ScalarEvolutionAnalysis: Stores pointers to
> > > > > > > > > TargetLibraryInfo,
> > > > > > > > > AssumptionCache, DominatorTree, LoopInfo
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > TargetLibraryAnalysis: Has no dependencies
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > TargetIRAnalysis: Has no dependencies.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > Function alias analyses: 3/5 keep pointers to other
> > > > > > > > > analyses
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > BasicAA: Keeps pointers to TargetLibraryInfo,
> > > > > > > > > AssumptionCache,
> > > > > > > > > DominatorTree, LoopInfo
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > CFLAA: Keeps pointer to TargetLibraryInfo
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > SCEVAA: Keeps pointer to ScalarEvolution
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > ScopedNoAliasAA: No dependencies
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > TypeBasedAA: No dependencies
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > > Total: 13/28 analyses (~50%) hold pointers to other
> > > > > > > > > analyses.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > Of the 15/28 analyses that don't hold pointers, 12/15
> > > > > > > > > simply
> > > > > > > > > have
> > > > > > > > > no
> > > > > > > > > dependencies. Only 3/15 (BPI, LoopInfo,
> > > > > > > > > DominanceFrontier)
> > > > > > > > > have
> > > > > > > > > dependencies that are used just for a "recalculate"
> > > > > > > > > step
> > > > > > > > > that
> > > > > > > > > retains no pointers.
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > > So I think it is fair to say that analyses which hold
> > > > > > > > > pointers
> > > > > > > > > to
> > > > > > > > > other analyses is not an exceptional case. In fact,
> > > > > > > > > analyses
> > > > > > > > > that
> > > > > > > > > use other analyses just for a "recalculate" step
> > > > > > > > > seems
> > > > > > > > > to
> > > > > > > > > be
> > > > > > > > > the
> > > > > > > > > exceptional case (only 3/28 or about 10%)
> > > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > Interesting!
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > Most of these look like they hold a pointer to the root
> > > > > > > > analysis
> > > > > > > > as
> > > > > > > > opposed to detailed objects *inside* the analysis?
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > It might make sense to try to handle this very specific
> > > > > > > > pattern
> > > > > > > > in
> > > > > > > > a
> > > > > > > > special way of overriding the invalidate routines is
> > > > > > > > too
> > > > > > > > error
> > > > > > > > prone.... We could try to make this work
> > > > > > > > "automatically"
> > > > > > > > but
> > > > > > > > I'm
> > > > > > > > worried this would be challenging to get right. Open to
> > > > > > > > suggestions
> > > > > > > > of course.
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > Any other ideas about what would make sense to handle
> > > > > > > > this?
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > > Does it make sense to override the invalidate routines
> > > > > > > > now
> > > > > > > > and
> > > > > > > > iterate from there? I feel like you've done a lot of
> > > > > > > > the
> > > > > > > > research
> > > > > > > > necessary for this already...
> > > > > > > 
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > I'll keep pushing forward tomorrow with building
> > > > > > > test-suite
> > > > > > > successfully using the new PM for the LTO pipeline (I was
> > > > > > > doing
> > > > > > > some
> > > > > > > unrelated LLD stuff for most of today). It will be
> > > > > > > interesting
> > > > > > > to
> > > > > > > see how many `invalidate` overrides will be needed to
> > > > > > > avoid
> > > > > > > these
> > > > > > > issues for just the LTO pipeline on test-suite.
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > I spent the better part of today working on this and will
> > > > > > continue
> > > > > > tomorrow; this problem seems nastier than I thought. For
> > > > > > some
> > > > > > reason
> > > > > > the LTO pipeline (or something about LTO) seems to hit on
> > > > > > these
> > > > > > issues much more (I'm talking like 40k lines of ASan error
> > > > > > reports
> > > > > > from building test-suite with the LTO pipeline in the new
> > > > > > PM;
> > > > > > per-TU
> > > > > > steps still using the old PM). Some notes:
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > - BasicAA's dependence on domtree and loopinfo in the new
> > > > > > PM
> > > > > > seems
> > > > > > to
> > > > > > account for quite a few of the problems.
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > - BasicAA and other stuff are marked (by overriding
> > > > > > `invalidate`
> > > > > > to
> > > > > > return false) to never be invalidated because they are
> > > > > > "stateless".
> > > > > > However they still hold pointers and so they do need to be
> > > > > > invalidated.
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > - CallGraph uses AssertingVH (PR28400) and so I needed a
> > > > > > workaround
> > > > > > similar to r274656 in various passes.
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > - D21921 is holding up -- I haven't hit any issues with the
> > > > > > core
> > > > > > logic of that patch.
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > - AAResults holds handles to various AA result objects.
> > > > > > This
> > > > > > means
> > > > > > it
> > > > > > pretty much always needs to be invalidated unless you are
> > > > > > sure
> > > > > > that
> > > > > > none of the AA's will get invalidated.
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > The existing `invalidate` method doesn't have the right
> > > > > > semantics
> > > > > > for
> > > > > > even an error-prone solution :( We are going to need to
> > > > > > make
> > > > > > some
> > > > > > significant changes to even get basic sanity I think.
> > > > > > Perhaps
> > > > > > each
> > > > > > analysis can expose a "preserve" static function. E.g.
> > > > > > instead
> > > > > > of
> > > > > > `PA.preserve<Foo>();` you have to do
> > > > > > `Foo::setPreserved(PA);`.
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > I'm actually not quite sure that that will even work. Once
> > > > > > I
> > > > > > have
> > > > > > test-suite fully building successfully with the LTO
> > > > > > pipeline
> > > > > > in
> > > > > > the
> > > > > > new PM I'll be able to give a more confident answer (esp.
> > > > > > w.r.t.
> > > > > > the
> > > > > > manager for different IRUnitT's).
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > But at this point I'm not confident running *any* pass
> > > > > > pipeline
> > > > > > in
> > > > > > the new PM without at least assertions+ASan.
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > We may want to have a proper design discussion around this
> > > > > > problem
> > > > > > though.
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > Also I'd like to have test-suite working (by hook or by
> > > > > > crook)
> > > > > > with
> > > > > > LTO in the new PM so we can get some numbers on the
> > > > > > resident
> > > > > > set
> > > > > > impact of all this caching; if it is really problematic
> > > > > > then
> > > > > > we
> > > > > > may
> > > > > > need to start talking front-and-center about different
> > > > > > invalidation
> > > > > > policies for keeping this in check instead of leaving it as
> > > > > > something that we will be able to patch later.
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > The more I think about it, the more I'm convinced that the
> > > > > > real
> > > > > > "hard" problem that the new PM is exposing us to is having
> > > > > > the
> > > > > > ability for any pass to ask for any analysis on any IRUnitT
> > > > > > (and
> > > > > > any
> > > > > > specific IRUnit of that IRUnitT) and have the result stored
> > > > > > somewhere and then invalidated. This means that
> > > > > > "getAnalysisUsage"
> > > > > > is not just a list of passes, but much more complicated and
> > > > > > is
> > > > > > essentially a set of arbitrary pairs "(analysis, IRUnit)"
> > > > > > (and
> > > > > > the
> > > > > > associated potential tangle of dependencies between the
> > > > > > state
> > > > > > cached
> > > > > > on these tuples). With the old PM, you essentially are
> > > > > > looking
> > > > > > at
> > > > > > a
> > > > > > problem of scheduling the lifetime of analyses of the same
> > > > > > IRUnit
> > > > > > intermingled with transformation passes on that same
> > > > > > IRUnit,
> > > > > > so
> > > > > > you
> > > > > > only have the "analysis" part of the tuple above, making
> > > > > > things
> > > > > > much
> > > > > > simpler (and handling dependencies is much simpler too).
> > > > > > We've
> > > > > > obviously outgrown this model with examples like LAA,
> > > > > > AssumptionCacheTracker, etc. that hack around this in the
> > > > > > old
> > > > > > PM.
> > > > > > We
> > > > > > may want to have a fresh re-examination of what problems we
> > > > > > are
> > > > > > exactly trying to solve.
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > For me, my main concern now is what changes need to be made
> > > > > > in
> > > > > > order
> > > > > > to feel confident running a pipeline in the new PM without
> > > > > > assertions+ASan.
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > Sorry for the long post, just brain-dumping before heading
> > > > > > home.
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > -- Sean Silva
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > -- Sean Silva
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > --
> 

> > Hal Finkel
> 
> > Assistant Computational Scientist
> 
> > Leadership Computing Facility
> 
> > Argonne National Laboratory
> 

-- 

Hal Finkel 
Assistant Computational Scientist 
Leadership Computing Facility 
Argonne National Laboratory 
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