[PATCH] D69125: [InstCombine] dropRedundantMaskingOfLeftShiftInput(): truncation (PR42563)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: spatel, nikic.
lebedev.ri added a project: LLVM.
Herald added a subscriber: hiraditya.
lebedev.ri updated this revision to Diff 225478.
lebedev.ri added a comment.

Drop redundant shadowing variable.


That fold keeps growing and growing :(
I think this may be one of the last pieces for it.

Since D67677 <https://reviews.llvm.org/D67677>/D67725 <https://reviews.llvm.org/D67725>, the fold knowns the general form
of the pattern - where some masking is needed:
https://rise4fun.com/Alive/F5R
https://rise4fun.com/Alive/gslRa

But there is one more huge piece missing - if you are extracting some bits,
it is not impossible that the origin is wider than the extraction,
i.e. there may be a truncation. And we don't deal with that yet.

But we can, and the generalization remains fully identical:
https://rise4fun.com/Alive/Uar
https://rise4fun.com/Alive/5SW

After a preparatory cleanup i think the diff looks rather clean.
One missing piece is that in some patterns (especially pat. b),
`-1` only needs to be `-1` in final type, but that is for later..

https://bugs.llvm.org/show_bug.cgi?id=42563


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D69125

Files:
  llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
  llvm/test/Transforms/InstCombine/partally-redundant-left-shift-input-masking-after-truncation-variant-a.ll
  llvm/test/Transforms/InstCombine/partally-redundant-left-shift-input-masking-after-truncation-variant-b.ll
  llvm/test/Transforms/InstCombine/partally-redundant-left-shift-input-masking-after-truncation-variant-c.ll
  llvm/test/Transforms/InstCombine/partally-redundant-left-shift-input-masking-after-truncation-variant-d.ll
  llvm/test/Transforms/InstCombine/partally-redundant-left-shift-input-masking-after-truncation-variant-e.ll
  llvm/test/Transforms/InstCombine/redundant-left-shift-input-masking-after-truncation-variant-a.ll
  llvm/test/Transforms/InstCombine/redundant-left-shift-input-masking-after-truncation-variant-b.ll
  llvm/test/Transforms/InstCombine/redundant-left-shift-input-masking-after-truncation-variant-c.ll
  llvm/test/Transforms/InstCombine/redundant-left-shift-input-masking-after-truncation-variant-d.ll
  llvm/test/Transforms/InstCombine/redundant-left-shift-input-masking-after-truncation-variant-e.ll
  llvm/test/Transforms/InstCombine/redundant-left-shift-input-masking-after-truncation-variant-f.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D69125.225478.patch
Type: text/x-patch
Size: 34467 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20191017/70f0cd5d/attachment-0001.bin>