define i32 @src(i32 %x) {
  %ctlz = call range(i32 1, 33) i32 @llvm.ctlz.i32(i32 %x, i1 false)
  %sub = sub i32 32, %ctlz
  %shl = shl i32 1, %sub
  %dec = add i32 %x, -1
  %ult = icmp ult i32 %dec, -2
  %sel = select i1 %ult, i32 %shl, i32 1
  ret i32 %sel
}

define i32 @tgt(i32 %x) {
  %ctlz = call range(i32 1, 33) i32 @llvm.ctlz.i32(i32 %x, i1 false)
  %1 = sub nsw i32 0, %ctlz
  %2 = and i32 %1, 31
  %sel = shl nuw i32 1, %2
  ret i32 %sel
}

----------------------------------------
define i32 @src(i32 %x) {
#0:
  %ctlz = ctlz i32 %x, 0
  %#range_0_%ctlz = !range i32 %ctlz, i32 1, i32 33
  %sub = sub i32 32, %#range_0_%ctlz
  %shl = shl i32 1, %sub
  %dec = add i32 %x, 4294967295
  %ult = icmp ult i32 %dec, 4294967294
  %sel = select i1 %ult, i32 %shl, i32 1
  ret i32 %sel
}
=>
define i32 @tgt(i32 %x) {
#0:
  %ctlz = ctlz i32 %x, 0
  %#range_0_%ctlz = !range i32 %ctlz, i32 1, i32 33
  %#1 = sub nsw i32 0, %#range_0_%ctlz
  %#2 = and i32 %#1, 31
  %sel = shl nuw i32 1, %#2
  ret i32 %sel
}
Transformation doesn't verify!

ERROR: Target is more poisonous than source

Example:
i32 %x = #xffffffff (4294967295, -1)

Source:
i32 %ctlz = #x00000000 (0)
i32 %#range_0_%ctlz = poison
i32 %sub = poison
i32 %shl = poison
i32 %dec = #xfffffffe (4294967294, -2)
i1 %ult = #x0 (0)
i32 %sel = #x00000001 (1)

Target:
i32 %ctlz = #x00000000 (0)
i32 %#range_0_%ctlz = poison
i32 %#1 = poison
i32 %#2 = poison
i32 %sel = poison
Source value: #x00000001 (1)
Target value: poison