[PATCH] D72573: [SelectionDAG] ComputeKnownBits - minimum leading/trailing zero bits in LSHR/SHL (PR44526)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: lebedev.ri, spatel, efriedma, craig.topper, regehr.
Herald added subscribers: atanasyan, jrtc27, hiraditya, nhaehnle, jvesely, sdardis.
Herald added a project: LLVM.

PR44526 - as detailed in https://blog.regehr.org/archives/1709 we don't make use of the known leading/trailing zeros for shifted values in cases where we don't know the shift amount value.

This patch adds support to SelectionDAG::ComputeKnownBits to use KnownBits::countMinTrailingZeros and countMinLeadingZeros to set the minimum guaranteed leading/trailing known zero bits.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72573

Files:
  llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  llvm/test/CodeGen/AArch64/hoist-and-by-const-from-lshr-in-eqcmp-zero.ll
  llvm/test/CodeGen/AArch64/hoist-and-by-const-from-shl-in-eqcmp-zero.ll
  llvm/test/CodeGen/AMDGPU/lshr.v2i16.ll
  llvm/test/CodeGen/AMDGPU/shl.ll
  llvm/test/CodeGen/AMDGPU/shl.v2i16.ll
  llvm/test/CodeGen/ARM/hoist-and-by-const-from-lshr-in-eqcmp-zero.ll
  llvm/test/CodeGen/ARM/hoist-and-by-const-from-shl-in-eqcmp-zero.ll
  llvm/test/CodeGen/BPF/shifts.ll
  llvm/test/CodeGen/Mips/llvm-ir/lshr.ll
  llvm/test/CodeGen/X86/avx2-shift.ll
  llvm/test/CodeGen/X86/avx2-vector-shifts.ll
  llvm/test/CodeGen/X86/hoist-and-by-const-from-lshr-in-eqcmp-zero.ll
  llvm/test/CodeGen/X86/vector-fshl-128.ll
  llvm/test/CodeGen/X86/vector-fshl-rot-128.ll
  llvm/test/CodeGen/X86/vector-fshr-128.ll
  llvm/test/CodeGen/X86/vector-fshr-rot-128.ll
  llvm/test/CodeGen/X86/vector-rotate-128.ll
  llvm/test/CodeGen/X86/vector-shift-lshr-128.ll
  llvm/test/CodeGen/X86/vector-shift-lshr-sub128.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D72573.237543.patch
Type: text/x-patch
Size: 43601 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200112/16e6fb9a/attachment.bin>