[PATCH] D138353: [Passes][VectorCombine] enable early run generally and try load folds

[Sanjay Patel via Phabricator via llvm-commits]

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An early run of VectorCombine was added with D102496 <https://reviews.llvm.org/D102496> specifically to deal with unnecessary vector ops produced with the C matrix extension. This patch is proposing to try those folds in general and add a pair of load folds to the menu.

The load transform will partly solve (see PhaseOrdering diffs) a longstanding vectorization perf bug by removing redundant loads via GVN:
issue #17113 <https://github.com/llvm/llvm-project/issues/17113>

The main reason for not enabling the extra pass generally in the initial patch was compile-time cost. The cost of VectorCombine was significantly (surprisingly) improved with:
87debdadaf18 <https://reviews.llvm.org/rG87debdadaf18f8a5c7e5d563889e10731dc3554d>
https://llvm-compile-time-tracker.com/compare.php?from=ffe05b8f57d97bc4340f791cb386c8d00e0739f2&to=87debdadaf18f8a5c7e5d563889e10731dc3554d&stat=instructions:u

...so the extra run is going to cost very little now - the total cost of the 2 runs should be less than the 1 run before that micro-optimization:
https://llvm-compile-time-tracker.com/compare.php?from=5e8c2026d10e8e2c93c038c776853bed0e7c8fc1&to=2c4b68eab5ae969811f422714e0eba44c5f7eefb&stat=instructions:u

It may be possible to reduce the cost slightly more with a few more earlier-exits like that, but it's probably in the noise based on timing experiments.


https://reviews.llvm.org/D138353

Files:
  llvm/lib/Passes/PassBuilderPipelines.cpp
  llvm/lib/Transforms/Vectorize/VectorCombine.cpp
  llvm/test/Other/new-pm-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/Other/new-pm-thinlto-prelink-pgo-defaults.ll
  llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
  llvm/test/Transforms/PhaseOrdering/X86/vec-load-combine.ll

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