[all-commits] [llvm/llvm-project] bfe2f5: [InstCombine] Fix buggy `(mul X, Y)` -> `(shl X, L...

[goldsteinn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: bfe2f5d38bb14bf7ce4f44d3de558fbc076bdc1a
      https://github.com/llvm/llvm-project/commit/bfe2f5d38bb14bf7ce4f44d3de558fbc076bdc1a
  Author: Noah Goldstein <goldstein.w.n at gmail.com>
  Date:   2023-04-18 (Tue, 18 Apr 2023)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
    M llvm/test/Transforms/InstCombine/div-shift.ll
    M llvm/test/Transforms/InstCombine/mul-pow2.ll

  Log Message:
  -----------
  [InstCombine] Fix buggy `(mul X, Y)` -> `(shl X, Log2(Y))` transform PR62175

Bug was because we recognized patterns like `(shl 4, Z)` as a power of
2 we could take Log2 of (`2 + Z`), but doing `(shl X, (2 + Z))` can
cause a poison shift.
    https://alive2.llvm.org/ce/z/yuJm_k

The fix is to verify that `Log2(Y)` will be a non-poisonous shift
amount. We can do this with:
    `nsw` flag:
        - https://alive2.llvm.org/ce/z/yyyJBr
        - https://alive2.llvm.org/ce/z/YgubD_
    `nuw` flag:
        - https://alive2.llvm.org/ce/z/-4mpyV
        - https://alive2.llvm.org/ce/z/a6ik6r
    Prove `Y != 0`:
        - https://alive2.llvm.org/ce/z/ced4su
        - https://alive2.llvm.org/ce/z/X-JJHb

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D148609


  Commit: 726f8ecac23bf04b60f9f079ee922b8a7a30457f
      https://github.com/llvm/llvm-project/commit/726f8ecac23bf04b60f9f079ee922b8a7a30457f
  Author: Noah Goldstein <goldstein.w.n at gmail.com>
  Date:   2023-04-18 (Tue, 18 Apr 2023)

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

  Log Message:
  -----------
  Recommit "[InstCombine] Add transforms for `(icmp {u|s}ge/le (xor X, Y), X)`" (2nd Try)

Wasn't related to the bug it was original thought to be causing.


  Commit: e846ec57cb80cd482b3a05b2b68c89775f806e6c
      https://github.com/llvm/llvm-project/commit/e846ec57cb80cd482b3a05b2b68c89775f806e6c
  Author: Noah Goldstein <goldstein.w.n at gmail.com>
  Date:   2023-04-18 (Tue, 18 Apr 2023)

  Changed paths:
    M llvm/lib/Analysis/ValueTracking.cpp
    M llvm/test/Analysis/ValueTracking/known-non-zero.ll
    M llvm/test/Transforms/InstCombine/ctpop-pow2.ll

  Log Message:
  -----------
  Recommit "[ValueTracking] Apply the isKnownNonZero techniques in `ashr`/`lshl` to `shl` and vice-versa" (2nd Try)

Wasn't related to the bug it was original thought to be causing.


Compare: https://github.com/llvm/llvm-project/compare/d771f54107c4...e846ec57cb80