[all-commits] [llvm/llvm-project] 9b183a: [NFC][InstSimplify] Add miscompiled testcase from ...

[Roman Lebedev via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 9b183a1452c7e5091be01661188b7cb04d842a4c
      https://github.com/llvm/llvm-project/commit/9b183a1452c7e5091be01661188b7cb04d842a4c
  Author: Roman Lebedev <lebedev.ri at gmail.com>
  Date:   2020-12-18 (Fri, 18 Dec 2020)

  Changed paths:
    M llvm/test/Transforms/InstSimplify/abs_intrinsic.ll

  Log Message:
  -----------
  [NFC][InstSimplify] Add miscompiled testcase from D87188/D87197

Thanks to Dave Green for producing an actionable reproducer!
It is (obviously) a miscompile:
```
----------------------------------------
define i32 @select_abs_of_abs_eq_wrong(i32 %x, i32 %y) {
%0:
  %abs = abs i32 %x, 0
  %neg = sub i32 0, %abs
  %cmp = icmp eq i32 %y, 0
  %sel = select i1 %cmp, i32 %neg, i32 %abs
  ret i32 %sel
}
=>
define i32 @select_abs_of_abs_eq_wrong(i32 %x, i32 %y) {
%0:
  %abs = abs i32 %x, 0
  ret i32 %abs
}
Transformation doesn't verify!
ERROR: Value mismatch

Example:
i32 %x = #xe0000000 (3758096384, -536870912)
i32 %y = #x00000000 (0)

Source:
i32 %abs = #x20000000 (536870912)
i32 %neg = #xe0000000 (3758096384, -536870912)
i1 %cmp = #x1 (1)
i32 %sel = #xe0000000 (3758096384, -536870912)

Target:
i32 %abs = #x20000000 (536870912)
Source value: #xe0000000 (3758096384, -536870912)
Target value: #x20000000 (536870912)

Alive2: Transform doesn't verify!

```


  Commit: e9289dc25f7923abff9ac762bd3f6819c0605f20
      https://github.com/llvm/llvm-project/commit/e9289dc25f7923abff9ac762bd3f6819c0605f20
  Author: Roman Lebedev <lebedev.ri at gmail.com>
  Date:   2020-12-18 (Fri, 18 Dec 2020)

  Changed paths:
    M llvm/lib/Analysis/InstructionSimplify.cpp
    M llvm/test/Transforms/InstSimplify/abs_intrinsic.ll

  Log Message:
  -----------
  [InstSimplify] Don't miscompile `X == 0 ? abs(X) : -abs(X) --> -abs(X)` xform

The transform wasn't checking that the LHS of the comparison
*is* the `X` in question...
This is the miscompile that was holding up D87188.

Thanks to Dave Green for producing an actionable reproducer!


  Commit: 897c985e1e21927b2870f964bb07ff293bd74407
      https://github.com/llvm/llvm-project/commit/897c985e1e21927b2870f964bb07ff293bd74407
  Author: Roman Lebedev <lebedev.ri at gmail.com>
  Date:   2020-12-18 (Fri, 18 Dec 2020)

  Changed paths:
    M clang/test/CodeGen/builtins-wasm.c
    M llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
    M llvm/test/Transforms/InstCombine/abs-1.ll
    M llvm/test/Transforms/InstCombine/abs_abs.ll
    M llvm/test/Transforms/InstCombine/call-callconv.ll
    M llvm/test/Transforms/InstCombine/cttz-abs.ll
    M llvm/test/Transforms/InstCombine/icmp.ll
    M llvm/test/Transforms/InstCombine/max-of-nots.ll
    M llvm/test/Transforms/InstCombine/select_meta.ll
    M llvm/test/Transforms/InstCombine/sub-of-negatible.ll
    M llvm/test/Transforms/PhaseOrdering/X86/vector-reductions.ll
    M llvm/test/Transforms/PhaseOrdering/min-max-abs-cse.ll

  Log Message:
  -----------
  [InstCombine] Canonicalize SPF to abs intrinsic

This patch enables canonicalization of SPF_ABS and SPF_ABS
to the abs intrinsic.

This is a recommit, the original try was
05d4c4ebc2fb006b8a2bd05b24c6aba10dd2eef8,
but it was reverted due to an apparent miscompile,
which since then has just been fixed by the previous commit.

Differential Revision: https://reviews.llvm.org/D87188


Compare: https://github.com/llvm/llvm-project/compare/5f75dcf5719f...897c985e1e21