Compile time regression after #154336

[piotrAMD]

#154336 causes some drastic compile time regressions for AMDGPU. In one real world case compilation time jumped from a fraction of second to over 1 hour, where most of the time is spent in the instcombine.
Here's the simplified reproducer repro.txt:

$ time ./opt_fail -passes="instcombine" -disable-output repro.txt

real 0m3,221s
user 0m3,208s
sys 0m0,013s

$ time ./opt_pass -passes="instcombine" -disable-output repro.txt

real 0m0,017s
user 0m0,008s
sys 0m0,009s