[PATCH] D88287: [NARY-REASSOCIATE] Support reassociation of min/max

[Nuno Lopes via Phabricator via llvm-commits]

nlopes added a comment.

This patch regressed the following tests:

- LLVM :: Transforms/NaryReassociate/nary-smax.ll
- LLVM :: Transforms/NaryReassociate/nary-smin.ll
- LLVM :: Transforms/NaryReassociate/nary-umax.ll
- LLVM :: Transforms/NaryReassociate/nary-umin.ll

The reason is that it doesn't account for undef values. Example:

  ----------------------------------------
  define i32 @smax_test1(i32 %a, i32 %b, i32 %c) {
  %0:
    %c1 = icmp sgt i32 %a, %b
    %smax1 = select i1 %c1, i32 %a, i32 %b
    %c2 = icmp sgt i32 %b, %c
    %smax2 = select i1 %c2, i32 %b, i32 %c
    %c3 = icmp sgt i32 %smax2, %a
    %smax3 = select i1 %c3, i32 %smax2, i32 %a
    %res = add i32 %smax1, %smax3
    ret i32 %res
  }
  =>
  define i32 @smax_test1(i32 %a, i32 %b, i32 %c) {
  %0:
    %c1 = icmp sgt i32 %a, %b
    %smax1 = select i1 %c1, i32 %a, i32 %b
    %1 = icmp sgt i32 %smax1, %c
    %smax3.nary = select i1 %1, i32 %smax1, i32 %c
    %res = add i32 %smax1, %smax3.nary
    ret i32 %res
  }
  Transformation doesn't verify!
  ERROR: Target's return value is more undefined
  
  Example:
  i32 %a = #x7fffffff (2147483647)
  i32 %b = #x00000000 (0)
  i32 %c = undef
  
  Source:
  i1 %c1 = #x1 (1)
  i32 %smax1 = #x7fffffff (2147483647)
  i1 %c2 = any
  i32 %smax2 = any
  i1 %c3 = #x0 (0)
  i32 %smax3 = #x7fffffff (2147483647)
  i32 %res = #xfffffffe (4294967294, -2)
  
  Target:
  i1 %c1 = #x1 (1)
  i32 %smax1 = #x7fffffff (2147483647)
  i1 %1 = #x0 (0)
  i32 %smax3.nary = #x03002006 (50339846)
  i32 %res = #x83002005 (2197823493, -2097143803)
  Source value: #xfffffffe (4294967294, -2)
  Target value: #x83002005 (2197823493, -2097143803)


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D88287/new/

https://reviews.llvm.org/D88287