[PATCH] D136806: [Pipelines] Introduce SROA after (full) loop unrolling

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
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I am surprised that we didn't do this already.

While it would be good to not introduce one more SROA invocation,
but instead move the one from `PassBuilder::buildFunctionSimplificationPipeline()`,
the existing test coverage says that is a bad idea,
though it would be fine compile-time wise: https://llvm-compile-time-tracker.com/compare.php?from=b150d34c47efbd8fa09604bce805c0920360f8d7&to=5a9a5c855158b482552be8c7af3e73d67fa44805&stat=instructions

So instead, i add yet another SROA run.
I have checked, and it needs to be at least after said full loop unrolling,
but i suppose placing it after InstCombine does not hurt.
Surprisingly, this is still fine compile-time wise: https://llvm-compile-time-tracker.com/compare.php?from=70324cd88328c0924e605fa81b696572560aa5c9&to=fb489bbef687ad821c3173a931709f9cad9aee8a&stat=instructions

Now, something in that link makes me cringe.
Compare it with https://llvm-compile-time-tracker.com/compare.php?from=70324cd88328c0924e605fa81b696572560aa5c9&to=d534377c0324a63ac26b990967577562e28a148f&stat=instructions
Those two commits share base, and don't functionally differ,
yet that `+0.23%` 'regression' is there in one of them.

I've encountered this in a real code, `SROA-after-final-loop-unrolling.ll` has been reduced from https://godbolt.org/z/fsdMhETh3


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D136806

Files:
  llvm/lib/Passes/PassBuilderPipelines.cpp
  llvm/test/Other/new-pm-defaults.ll
  llvm/test/Other/new-pm-lto-defaults.ll
  llvm/test/Other/new-pm-thinlto-defaults.ll
  llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
  llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
  llvm/test/Transforms/Coroutines/coro-retcon-resume-values.ll
  llvm/test/Transforms/PhaseOrdering/X86/SROA-after-final-loop-unrolling.ll
  llvm/test/Transforms/PhaseOrdering/single-iteration-loop-sroa.ll

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