[PATCH] D129612: [Reassociate] Cleanup minor missed optimizations

[Warren Ristow via Phabricator via llvm-commits]

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In analyzing issue #56483, it was noticed that running `opt` with
`-reassociate` was missing some minor optimizations.  For example,
there were cases where the running `opt` on IR with floating-point
instructions that have the `fast` flags applied, sometimes resulted in
less efficient code than the input IR (things like dead instructions
left behind, and missed reassociations).  These were sometimes noted
in the test-files with TODOs, to investigate further.  This commit
fixes some of these problems, removing some TODOs in the process.

FTR, I refer to these as "minor" missed optimizations, because when
running a full clang/llvm compilation, these inefficiencies are not
happening, as other passes clean that residue up.  Regardless, having
cleaner IR produced by `opt`, makes assessing the quality of fixes done
in `opt` easier.


https://reviews.llvm.org/D129612

Files:
  llvm/lib/Transforms/Scalar/Reassociate.cpp
  llvm/test/Transforms/Reassociate/fast-ReassociateVector.ll
  llvm/test/Transforms/Reassociate/fast-basictest.ll
  llvm/test/Transforms/Reassociate/pr42349.ll

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