[PATCH] D50222: [CodeGen] [SelectionDAG] More efficient code for X % C == 0

[Dmytro Shynkevych via Phabricator via llvm-commits]

hermord updated this revision to Diff 159505.
hermord added a comment.

As pointed out by @lebedev.ri, tests were inadequate. Added new tests and stepped through existing ones, adding descriptions. This uncovered two more bugs, which were also fixed here (an extraneous `Q.lshrInPlace()` and division by D instead of D0). As far as I can see, the coverage now seems reasonable; please point out any cases I missed.

Regarding @majnemer's suggestion, my bad: I should have mentioned in the last update that this algorithm actually assumes that D is positive ("because d is odd and, as we are assuming, positive and not equal to 1..." [Hacker's Delight, p.227]). It probably can be adapted to the `D < 0` case with some tweaks, but it seems easier to just take the absolute value of `D` since this does not change the answer.


Repository:
  rL LLVM

https://reviews.llvm.org/D50222

Files:
  include/llvm/CodeGen/TargetLowering.h
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  lib/CodeGen/SelectionDAG/TargetLowering.cpp
  test/CodeGen/Hexagon/swp-const-tc2.ll
  test/CodeGen/X86/jump_sign.ll
  test/CodeGen/X86/rem.ll
  test/CodeGen/X86/vselect-avx.ll

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