[all-commits] [llvm/llvm-project] b2fe02: [InstCombine][test] add tests for icmp ult with co...

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  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b2fe025707aae780d88db2446fc1ce618e40bdb3
      https://github.com/llvm/llvm-project/commit/b2fe025707aae780d88db2446fc1ce618e40bdb3
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2021-06-30 (Wed, 30 Jun 2021)

  Changed paths:
    M llvm/test/Transforms/InstCombine/icmp-add.ll

  Log Message:
  -----------
  [InstCombine][test] add tests for icmp ult with constant and offset; NFC

This is the 'ult' sibling pattern for:
c7b658aeb526c3e6


  Commit: 0c400e8953069888315f85d62780839dccbaa33c
      https://github.com/llvm/llvm-project/commit/0c400e8953069888315f85d62780839dccbaa33c
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2021-06-30 (Wed, 30 Jun 2021)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    M llvm/test/Transforms/InstCombine/icmp-add.ll

  Log Message:
  -----------
  [InstCombine] fold icmp ult of offset value with constant

This is one sibling of the fold added with c7b658aeb526 .

(X + C2) <u C --> X >s ~C2 (if C == C2 + SMIN)
I'm still not sure how to describe it best, but we're
translating 2 constants from an unsigned range comparison
to signed because that eliminates the offset (add) op.

This could be extended to handle the more general (non-constant)
pattern too:
https://alive2.llvm.org/ce/z/K-fMBf

  define i1 @src(i8 %a, i8 %c2) {
    %t = add i8 %a, %c2
    %c = add i8 %c2, 128 ; SMIN
    %ov = icmp ult i8 %t, %c
    ret i1 %ov
  }

  define i1 @tgt(i8 %a, i8 %c2) {
    %not_c2 = xor i8 %c2, -1
    %ov = icmp sgt i8 %a, %not_c2
    ret i1 %ov
  }


Compare: https://github.com/llvm/llvm-project/compare/b41b4148e7b9...0c400e895306