[MachineSink] llc hang caused by #115111

[dtcxzyw]

Reproducer:

; timeout 0.5s bin/llc reduced.ll
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define i32 @main() {
entry:
  br label %lbl_1680.i.us.i.outer

lbl_1680.i.us.i:                                  ; preds = %lbl_1680.i.us.i.outer, %lbl_1680.i.us.i
  br i1 %tobool415.not.i99.us.i, label %lbl_1680.i.us.i.outer, label %lbl_1680.i.us.i

lbl_1680.i.us.i.outer:                            ; preds = %lbl_1680.i.us.i, %entry
  %tobool415.not.i99.us.i = phi i1 [ true, %entry ], [ false, %lbl_1680.i.us.i ]
  br label %lbl_1680.i.us.i
}

Bisected to #115111.
cc @paperchalice @qcolombet @chapuni

[paperchalice]

Reverted. Thanks for the reproducer. Need some time to troubleshoot it...

[paperchalice]

Opened #119547.