[Bug 1811798]

[Jakub-gcc]

So, to me this looks like a backend bug, using dead_or_set_p in a splitter when the split passes don't really compute the note problem.  Seems s390 is the only backend that does this, other backends use dead_or_set_p either only in peephole2s (which is fine, peephole2 pass starts with
  df_set_flags (DF_LR_RUN_DCE);
  df_note_add_problem ();
  df_analyze ();
and even when many targets don't use df_or_set_p, they do use peep2_dead*), or (cris) in delayed branch scheduling (I believe that doesn't guarantee that either).  Can't what you are doing in the splitters be done in define_peephole2 instead?

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https://bugs.launchpad.net/bugs/1811798

Title:
  gcc 8 miscompiles scipy/optimize/minpack/qrsolv.f

Status in gcc:
  In Progress
Status in gcc-8 package in Ubuntu:
  New
Status in imexam package in Ubuntu:
  New
Status in python-scipy package in Ubuntu:
  New
Status in python-scipy package in Debian:
  New

Bug description:
  Originally reported in https://bugs.debian.org/906198

  The following simple test fails on s390x:

  ---------------------------8<------------------------------
  import numpy as np
  from scipy.optimize import leastsq

  y = np.array([0., 1., 1., 2., 1., 1., 0.])
  x = np.arange(len(y))

  def func(par):
      return par[2] * np.exp(-(x - par[0])**2/par[1]) - y

  print(leastsq(func, [0,1,0]))
  ---------------------------8<------------------------------

  The expected result is

  (array([3.        , 4.42280548, 1.67210345]), 1)

  while on S390x, one gets

  (array([0.        , 1.        , 0.34027645]), 3)

  
  Further information from https://bugs.debian.org/915738

  The bug seems to be a miscompilation of scipy/optimize/minpack/qrsolv.f
  with -funroll-loops. Removing -funroll-loops is enough to get the
  leastsq testcase to pass.

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