[Bug rtl-optimization/109009] Shrink Wrap missed opportunity

[jskumari at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109009

--- Comment #3 from Surya Kumari Jangala <jskumari at gcc dot gnu.org> ---
For the working case:

 * Input RTL to the IRA pass:
BB2:
  set r123, r4
  set r122, r3
  set r120, compare(r123, 0)
  set r118, r122
  if r120 jump BB4 else jump BB3
BB3:
  call bar()
BB4:
  set r3, r118
  return


 * RTL after the IRA pass:
same as the input

 * RTL after reload pass:
BB2:
  set r100, compare(r4, 0)
  if r100 jump BB4 else jump BB3
BB3:
  set mem(r1+32), r3
  call bar()
  set r3, mem(r1+32)

-----------

For the failing case:

 * Input RTL to the IRA pass:
BB2:
  set r123, r4
  set r122, r3
  set r120, compare(r123, 0)
  set r118, r122
  if r120 jump BB4 else jump BB3
BB3:
  call bar()
BB4:
  set r3, r118+1
  return r3

  * RTL after IRA pass
same as the input

  * RTL after reload pass
BB2:
  set r100, compare(r4, 0)
  set r31, r3
  if r100 jump BB4 else jump BB3
BB3:
  call bar()
BB4:
  set r3, r31+1
  return r3

--------

After the IRA pass, the IR looks very similar in both the working and failing
testcases. But the reload pass produces different IR. 
The live ranges seem to be properly split after IRA. I will be checking why the
reload/LRA pass produces different IR.