Re: [PATCH testsuite]Require vect_cond_mixed for test case gcc.dg/vect/pr56541.c

["Bin.Cheng" <amker dot cheng at gmail dot com>]

On Thu, Aug 11, 2016 at 11:38 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Thu, Aug 11, 2016 at 11:56 AM, Bin.Cheng <amker.cheng@gmail.com> wrote:
>> On Thu, Aug 11, 2016 at 10:50 AM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>> On Wed, Aug 10, 2016 at 5:58 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
>>>> Hi,
>>>> Due to some reasons, tree-if-conv.c now factors floating point comparison out of cond_expr,
>>>> resulting in mixed types in it.  This does help CSE on common comparison operations.
>>>> Only problem is that test gcc.dg/vect/pr56541.c now requires vect_cond_mixed to be
>>>> vectorized.  This patch changes the test in that way.
>>>> Test result checked.  Is it OK?
>>>
>>> Hmm, I think the fix is to fix if-conversion not doing that.  Can you
>>> track down why this happens?
>> Hmm, but there are several common floating comparison operations in
>> the case, by doing this, we could do CSE on GIMPLE, otherwise we
>> depends on RTL optimizers.
>
> I see.
>
>> I thought we prefer GIMPLE level
>> transforms?
>
> Yes, but the vectorizer is happier with the conditions present in the COND_EXPR
> and thus we concluded we always want to have them there.  forwprop will
> also aggressively put them back.  Note that we cannot put back
> tree_could_throw_p
> conditions (FP compares with signalling nans for example) to properly model EH
> (though for VEC_COND_EXPRs we don't really care here).
>
> Note that nothing between if-conversion and vectorization will perform
> the desired
> CSE anyway.
Hi Richard,
I looked into this one and found it was not if-conv factors cond_expr
out.  For test case:

  for (i=0; i!=1024; ++i)
    {
      float rR = a*z[i];
      float rL = b*z[i];
      float rMin = (rR<rL) ? rR : rL;
      float rMax = (rR<rL) ? rL : rR;
      rMin = (rMax>0) ? rMin : rBig;
      rMin = (rMin>0) ? rMin : rMax;
      ok[i] = rMin-c<rMax+d;
    }
Dump before jump threading is like:

  <bb 7>:
  # iftmp.3_12 = PHI <rL_18(5), rR_17(6)>
  if (iftmp.3_12 > 0.0)
    goto <bb 9>;
  else
    goto <bb 8>;

  <bb 8>:

  <bb 9>:
  # iftmp.4_13 = PHI <iftmp.2_11(7), 1.5e+2(8)>
  if (iftmp.4_13 > 0.0)
    goto <bb 11>;
  else
    goto <bb 10>;

  <bb 10>:

  <bb 11>:
  # iftmp.5_14 = PHI <iftmp.4_13(9), iftmp.3_12(10)>

Jump thread in dom pass threads edges (bb7 -> bb8 -> ... bb11) to (bb6
-> bb12 -> bb9) as below:

  <bb 6>:
  # iftmp.3_12 = PHI <rL_18(4), rR_17(5), rL_18(11)>
  # iftmp.2_23 = PHI <iftmp.2_11(4), iftmp.2_11(5), iftmp.2_10(11)>
  if (iftmp.3_12 > 0.0)
    goto <bb 7>;
  else
    goto <bb 12>;

  <bb 7>:
  # iftmp.4_13 = PHI <iftmp.2_23(6)>
  if (iftmp.4_13 > 0.0)
    goto <bb 9>;
  else
    goto <bb 8>;

  <bb 8>:

  <bb 9>:
  # iftmp.5_14 = PHI <iftmp.4_13(7), iftmp.3_12(8), 1.5e+2(12)>

  //...
  <bb 12>:
  # iftmp.4_22 = PHI <1.5e+2(6)>
  goto <bb 9>;

This transform saves one comparison on the path, but creates multi-arg
phi, resulting in cond_expr being factored out.

Looks like threading corrupts vectorization opportunity for target
doesn't support vect_cond_mixed, but I guess it's hard to tell in
threading itself.  Any ideas?

Thanks,
bin