[PATCH] D37121: [DivRemHoist] add a pass to move div/rem pairs into the same block (PR31028)

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
Herald added subscribers: kristof.beyls, mgorny, mcrosier, mehdi_amini, aemerson.

This is intended to be the same functionality as https://reviews.llvm.org/D31037 (EarlyCSE) but implemented as an independent pass, so there's no stretching of scope and feature creep for an existing pass. I also proposed a weaker version of this for SimplifyCFG in https://reviews.llvm.org/D30910. And I initially had almost this same functionality as another lump of CGP in the motivating example of PR31028 ( https://bugs.llvm.org/show_bug.cgi?id=31028 ). It's been a long road. :)

The advantage of positioning this ahead of SimplifyCFG / InstCombine in the pass pipeline is that we'll reduce the positive test cases to a single block:

  %rem = urem i8 %a, %b
  %div = udiv i8 %a, %b
  %cmp = icmp eq i8 %div, 42
  %sel = select i1 %cmp, i8 %rem, i8 3
  ret i8 %sel

...and that can lead to better codegen even for targets that don't have a joint divrem instruction. https://reviews.llvm.org/D30910 has an AArch64 example of that.


https://reviews.llvm.org/D37121

Files:
  include/llvm/InitializePasses.h
  include/llvm/Transforms/Scalar.h
  include/llvm/Transforms/Scalar/DivRemHoist.h
  lib/Passes/PassBuilder.cpp
  lib/Passes/PassRegistry.def
  lib/Transforms/IPO/PassManagerBuilder.cpp
  lib/Transforms/Scalar/CMakeLists.txt
  lib/Transforms/Scalar/DivRemHoist.cpp
  lib/Transforms/Scalar/Scalar.cpp
  test/Transforms/DivRemHoist/div-rem-pairs.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D37121.112612.patch
Type: text/x-patch
Size: 17636 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170824/6956d96b/attachment.bin>