[PATCH] D84309: [InstCombine] Preserve FMA opportunities when combining PHI nodes

[Nemanja Ivanovic via Phabricator via llvm-commits]

nemanjai created this revision.
nemanjai added reviewers: majnemer, spatel, efriedma, craig.topper, PowerPC.
Herald added subscribers: wuzish, hiraditya.
Herald added a project: LLVM.

We currently unconditionally combine multiple `FAdd` instructions that feed a PHI into one. However, if at least some of those are fed by `FMul`'s and the instructions allow contraction, this takes away opportunities to produce FMA's.

This patch just adds a check for this situation and prevents combining if such a situation is encountered.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D84309

Files:
  llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
  llvm/test/Transforms/InstCombine/phi-preserve-fmas.ll

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