[llvm-dev] Should Verifier be an analysis?

[Chijun Sima via llvm-dev]

Thanks for your reply.

I found I happened to switch assertions on when benchmarking. But, the
Verifier still runs under Release+without assertions and still
consumes an approximately 7% of the time used by the whole
DominatorTree related calculations when optimizing SQLite with opt
-O3.

The verifier doesn't invalidate DT, it just construct one explicitly
as in https://github.com/llvm-mirror/llvm/blob/master/lib/IR/Verifier.cpp#L325-L332
Preserving the freshly calculated DomTree would be nice.

On Fri, Jul 13, 2018 at 2:13 AM Hal Finkel <hfinkel at anl.gov> wrote:
>
>
> On 07/12/2018 12:43 PM, Chijun Sima via llvm-dev wrote:
> > Hi,
> >
> > I am wondering whether it is feasible to preserve the DominatorTree
> > which is recalculated in the Verifier by making Verifier into an
> > analysis. This recalculation actually consumes an approximately 7% of
> > the time used by the whole DominatorTree related calculations when
> > optimizing SQLite with opt -O3.
>
> The verifier itself should not be invalidating the DT. It has this:
>
> struct VerifierLegacyPass : public FunctionPass {
> ...
>   void getAnalysisUsage(AnalysisUsage &AU) const override {
>     AU.setPreservesAll();
>
> I assume that the problem is that other passes are invalidating the DT
> in between verifier runs?
>
> Are you benchmarking with asserts enabled? I was under the impression
> that we skipped the verifier runs in release builds with asserts disabled.
>
>  -Hal
>
> >
> > Best,
> > Chijun Sima
> >
> > On Thu, Jul 12, 2018 at 11:19 PM Son Tuan VU via llvm-dev
> > <llvm-dev at lists.llvm.org> wrote:
> >> Hello all,
> >>
> >> I came across the code of Verifier, and see that it doesn't modify the IR at all. Why it is not considered as an analysis pass?
> >>
> >> Actually, this will have impact on debugify-each and print-before/after-all: we are not supposed to print/debugify Verifier pass, but since Verifier is declared as a transformation (well, a non-analysis) pass, we actually do print/debugify it.
> >>
> >> Thanks for your help!
> >>
> >> Son Tuan Vu
> >> _______________________________________________
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> >> llvm-dev at lists.llvm.org
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>
> --
> Hal Finkel
> Lead, Compiler Technology and Programming Languages
> Leadership Computing Facility
> Argonne National Laboratory
>