[PATCH] D136559: [DAG] Fold (abs (sign_extend_inreg x)) -> (zero_extend (abs (truncate x))) (PR43370)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: spatel, craig.topper, nikic, lebedev.ri.
Herald added subscribers: StephenFan, ecnelises, pengfei, hiraditya.
Herald added a project: All.
RKSimon requested review of this revision.
Herald added a project: LLVM.

If the upper half of an abs() is all sign bits, then we can perform the abs() using just the lower half and then zero extend.

I've limited the DAG combine to only sign_extend_inreg (and free truncate/zero_extend) to minimise any later promotion issues, but for legalization a similar fold can use ComputeNumSignBits to be more aggressive.

Alive2: https://alive2.llvm.org/ce/z/y32fS4

Fixes #43370


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D136559

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
  llvm/test/CodeGen/X86/abs.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D136559.469995.patch
Type: text/x-patch
Size: 4162 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20221023/7fe67b96/attachment.bin>