[all-commits] [llvm/llvm-project] 0d674c: [Mem2Reg] Extract code for converting !nonull to a...

Nikita Popov via All-commits all-commits at lists.llvm.org
Thu Jan 12 07:42:02 PST 2023

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0d674cf0eae84a7b83999d2122c1609a8ee2b16d
  Author: Nikita Popov <npopov at redhat.com>
  Date:   2023-01-12 (Thu, 12 Jan 2023)

  Changed paths:
    M llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

  Log Message:
  [Mem2Reg] Extract code for converting !nonull to assume (NFC)

  Commit: 4f772b095525059521f2f88112d29dcfaa178101
  Author: Nikita Popov <npopov at redhat.com>
  Date:   2023-01-12 (Thu, 12 Jan 2023)

  Changed paths:
    M llvm/include/llvm/Analysis/LazyValueInfo.h
    M llvm/lib/Analysis/LazyValueInfo.cpp
    M llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
    M llvm/test/Transforms/CorrelatedValuePropagation/cond-at-use.ll

  Log Message:
  [LVI][CVP] Make use of condition known at use

When an instruction is only used in a select or phi operand, we might
be able to make use of additional information from the select/branch
condition. For example in

  %sub = call i16 @llvm.usub.sat.i16(i16 %x, i16 10)
  %cmp = icmp uge i16 %x, 10
  %sel = select i1 %cmp, i16 %sub, i16 42

the usub.sat is only used in a select where %x uge 10 is known to
hold, so we can fold it based on that knowledge.

This addresses the regression reported at
https://reviews.llvm.org/D140798#4039748, but also provides a
solution to a recurring problem we've had, where we fail to make
use of range information after a branch+phi has been converted
into a select. Our current solution to this is to hope that IPSCCP
can perform the fold before that happens, but handling this in LVI
is a somewhat more general solution.

Currently we only make use of this for the willNotOverflow() fold,
but I plan to adjust other folds to use the new API as well.

Differential Revision: https://reviews.llvm.org/D141482

Compare: https://github.com/llvm/llvm-project/compare/bff31d0836bf...4f772b095525

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