incorrect reassociation at low bitwidth

[regehr]

here's a function:

define i3 @f(i3 %0) {
  %2 = mul i3 %0, %0
  %3 = mul i3 %2, %0
  %4 = mul i3 %3, %0
  %5 = mul nsw i3 %4, %0
  ret i3 %5
}

reassociate seems to be getting it wrong:

Johns-MacBook-Pro:reduce regehr$ ~/alive2-regehr/build/alive-tv reduced.ll -passes=reassociate

----------------------------------------
define i3 @f(i3 %#0) {
#1:
  %#2 = mul i3 %#0, %#0
  %#3 = mul i3 %#2, %#0
  %#4 = mul i3 %#3, %#0
  %#5 = mul nsw i3 %#4, %#0
  ret i3 %#5
}
=>
define i3 @f(i3 %#0) {
#1:
  %#2 = mul i3 %#0, %#0
  %#3 = mul nsw i3 %#2, %#0
  ret i3 %#3
}
Transformation doesn't verify!

ERROR: Target is more poisonous than source

Example:
i3 %#0 = #x6 (6, -2)

Source:
i3 %#2 = #x4 (4, -4)
i3 %#3 = #x0 (0)
i3 %#4 = #x0 (0)
i3 %#5 = #x0 (0)

Target:
i3 %#2 = #x4 (4, -4)
i3 %#3 = poison
Source value: #x0 (0)
Target value: poison

Summary:
  0 correct transformations
  1 incorrect transformations
  0 failed-to-prove transformations
  0 Alive2 errors
Johns-MacBook-Pro:reduce regehr$ 

cc @nunoplopes

[dtcxzyw]

Introduced by d7aeefe.