[PATCH] D42309: [LV] Use Demanded Bits and ValueTracking for reduction type-shrinking

[Matthew Simpson via Phabricator via llvm-commits]

mssimpso created this revision.
mssimpso added reviewers: Ayal, gilr, mkuper.
mssimpso edited the summary of this revision.

The type-shrinking logic in reduction detection, although narrow in scope, is also rather ad-hoc, which has led to bugs (e.g., PR35734). This patch modifies the approach to rely on the demanded bits and value tracking analyses, if available. We currently perform type-shrinking separately for reductions and other instructions in the loop. Long-term, we should probably think about computing minimal bit widths in a more complete way for the loops we want to vectorize.

Reference: https://bugs.llvm.org/show_bug.cgi?id=35734


Repository:
  rL LLVM

https://reviews.llvm.org/D42309

Files:
  include/llvm/Transforms/Utils/LoopUtils.h
  lib/Transforms/Utils/LoopUtils.cpp
  lib/Transforms/Vectorize/LoopVectorize.cpp
  test/Transforms/LoopVectorize/reduction-small-size.ll

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