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From: "amker at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/62173] [5.0 regression] 64bit Arch can't ivopt while 32bit Arch can
Date: Fri, 30 Jan 2015 06:42:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62173

--- Comment #31 from amker at gcc dot gnu.org ---
So cand_value_at (loop, cand, use->stmt, desc->niter, &bnd) with arguments as
below:

  cand->iv->base:
      (unsigned long) ((char *) &A + (sizetype) i_6(D))
  cand->iv->step:
      0xFFFFFFFFFFFFFFFF
  desc->niter:
      (unsigned int)(i_6(D) + -1)
  use->stmt:
      is after increment

The result calculated should like below:
  iv->base + iv->step * (unsigned long)niter + step
    <=>
  (unsigned long) ((char *) &A + (sizetype) i_6(D))
    +
  0xFFFFFFFFFFFFFFFF * ((unsigned long)(unsigned int)(i_6(D) + -1))
    +
  0xFFFFFFFFFFFFFFFF

Even with range information [1, 10] for i_6(D), and we can prove that niter's
range is [0, 9].  We can't prove it equals to:
  (unsigned long)((char *) &A)

This is because we use unsigned type for step and lose the sign information?
And this can't be fixed even with the proper range information.  Is this
understanding correct?  Or anything I should do to achieve that?

Thanks very much.