[PATCH] D125987: [SLP] Account for cost of removing FMA opportunities by horizontal reduction

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:9675
+// the tree of multiplies.
+static InstructionCost getFMALossCost(const TargetTransformInfo *TTI,
+                                      Value *TreeRootOp, FastMathFlags FMF,
----------------
wjschmidt wrote:
> ABataev wrote:
> > wjschmidt wrote:
> > > ABataev wrote:
> > > > I think it must be a part of TTI::getArithmeticReductionCost
> > > Because this will also be called in a case where it's not part of a reduction, I'd like to keep it separate.  (See my comment in the summary.)  Perhaps I shouldn't have split the patches so this would be more evident.
> > Anyway, maybe better to make it a part of TTI rather than put it to SLPVectorizer?
> That's certainly possible, and probably a good idea.  We'd need to pull out the final multiplication by Width and the SLP-specific debug stuff, but with that done it would fit nicely in TTI, and there might be potential for reuse.
Ideally the getArithmeticReductionCost costs wouldn't be affected but getArithmeticInstrCost could be adjusted to account for potential FMA patterns in the scalar/vector FADD costs


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D125987/new/

https://reviews.llvm.org/D125987