[InstCombine] Commuted pattern is not handled

[dtcxzyw]

This issue lists all the missed optimization issues related to commutative patterns in InstCombine.

[dtcxzyw]

https://godbolt.org/z/5bh5v8Tn6

define i1 @no_masks_with_logical_or1(i32 %a, i32 %b, i32 noundef %c) {
  %cmp1 = icmp ne i32 %a, 0
  %cmp2 = icmp ne i32 %b, 63
  %or1 = select i1 %cmp1, i1 true, i1 %cmp2
  %cmp3 = icmp ne i32 %c, 0
  %or2 = or i1 %or1, %cmp3
  ret i1 %or2
}

define i1 @no_masks_with_logical_or2(i32 %a, i32 %b, i32 noundef %c) {
  %cmp1 = icmp ne i32 %a, 0
  %cmp2 = icmp ne i32 %b, 63
  %or1 = select i1 %cmp1, i1 true, i1 %cmp2
  %cmp3 = icmp ne i32 %c, 0
  %or2 = or i1 %cmp3, %or1
  ret i1 %or2
}

define i1 @no_masks_with_logical_or1(i32 %a, i32 %b, i32 noundef %c) {
  %cmp2 = icmp ne i32 %b, 63
  %1 = or i32 %a, %c
  %2 = icmp ne i32 %1, 0
  %or2 = select i1 %2, i1 true, i1 %cmp2
  ret i1 %or2
}

define i1 @no_masks_with_logical_or2(i32 %a, i32 %b, i32 noundef %c) {
  %cmp1 = icmp ne i32 %a, 0
  %cmp2 = icmp ne i32 %b, 63
  %or1 = select i1 %cmp1, i1 true, i1 %cmp2
  %cmp3 = icmp ne i32 %c, 0
  %or2 = or i1 %cmp3, %or1
  ret i1 %or2
}

[dtcxzyw]

https://godbolt.org/z/4xa1fG3a9

define i1 @icmp_equality_test_commute_select1(i64 %X, i64 %Y, i64 %Z) {
entry:
  %XeqZ = icmp eq i64 %X, %Z
  %YeqZ = icmp eq i64 %Y, %Z
  %XeqY = icmp eq i64 %X, %Y
  %and = select i1 %YeqZ, i1 false, i1 %XeqY
  %equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
  ret i1 %equal
}

define i1 @icmp_equality_test_commute_select2(i64 %X, i64 %Y, i64 %Z) {
entry:
  %XeqZ = icmp eq i64 %X, %Z
  %YeqZ = icmp ne i64 %Y, %Z
  %XeqY = icmp eq i64 %X, %Y
  %and = select i1 %YeqZ, i1 %XeqY, i1 false
  %equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
  ret i1 %equal
}

define i1 @icmp_equality_test_commute_select1(i64 %X, i64 %Y, i64 %Z) {
  %XeqY = icmp eq i64 %X, %Y
  ret i1 %XeqY
}

define i1 @icmp_equality_test_commute_select2(i64 %X, i64 %Y, i64 %Z) {
  %XeqZ = icmp eq i64 %X, %Z
  %YeqZ = icmp ne i64 %Y, %Z
  %XeqY = icmp eq i64 %X, %Y
  %and = select i1 %YeqZ, i1 %XeqY, i1 false
  %equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
  ret i1 %equal
}

[dtcxzyw]

https://godbolt.org/z/Ez3hEb8vs

define i32 @poo2(i32 %a, i32 %b, i32 %c, i32 %d) {
  %t0 = icmp slt i32 %a, %b
  %iftmp.0.0 = select i1 %t0, i32 -1, i32 0
  %t1 = and i32 %iftmp.0.0, %c
  %iftmp = select i1 %t0, i32 0, i32 -1
  %t2 = and i32 %iftmp, %d
  %t3 = or i32 %t1, %t2
  ret i32 %t3
}

define i32 @poo3(i32 %a, i32 %b, i32 %c, i32 %d) {
  %t0 = icmp sge i32 %a, %b
  %iftmp.0.0 = select i1 %t0, i32 0, i32 -1
  %t1 = and i32 %iftmp.0.0, %c
  %iftmp = select i1 %t0, i32 0, i32 -1
  %t2 = and i32 %iftmp, %d
  %t3 = or i32 %t1, %t2
  ret i32 %t3
}

define i32 @poo2(i32 %a, i32 %b, i32 %c, i32 %d) {
  %t0.not = icmp slt i32 %a, %b
  %t3 = select i1 %t0.not, i32 %c, i32 %d
  ret i32 %t3
}

define i32 @poo3(i32 %a, i32 %b, i32 %c, i32 %d) {
  %t0.not = icmp slt i32 %a, %b
  %1 = or i32 %c, %d
  %t3 = select i1 %t0.not, i32 %1, i32 0
  ret i32 %t3
}

[dtcxzyw]

@nikic @goldsteinn
What is the policy for these issues? There is no reason not to support the commuted versions of these patterns.
However, as these issues have existed for a long time and there are no reports from downstream users, can we just delete the code entirely if there is no evidence of real-world usefulness?

[nikic]

I don't think it's possible to answer this in general. Adding support for the commuted pattern is always safe. To drop the transform we should do some investigation (like try to find out why it was added in the first place) on a case by case basis.