[PATCH] D58009: [DAGCombine] Simplify funnel shifts with undef/zero args to bitshifts

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri accepted this revision.
lebedev.ri added a comment.
This revision is now accepted and ready to land.

Looks ok to me.



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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:7169
+  // iff We know the shift amount is in range.
+  // TODO: when is it worth doing SUB(BW, N2) as well?
+  if (isPowerOf2_32(BitWidth)) {
----------------
Hmm, if `FeatureSlowSHLD` is set, or we have BMI2 (and thus sh[lr]x, not depending on `%cl` reg)?
Also, to be noted `sub 32, n` should get folded to `neg n`, IIRC.


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https://reviews.llvm.org/D58009