[PATCH] Improve var_bound range test opt (PR tree-optimization/81655)

[Jakub Jelinek]

Hi!

For the PR81588 testcase, on targets with branch cost 1, we end up with:
  b.0_1 = b;
  _2 = (long long int) b.0_1;
  a.1_3 = a;
  _4 = _2 > a.1_3;
  _5 = (int) _4;
  if (a.1_3 < 0)
    goto <bb 4>; [36.00%] [count: INV]
  else
    goto <bb 3>; [64.00%] [count: INV]

  <bb 3> [64.00%] [count: INV]:
  if (_4 != 1)
    goto <bb 4>; [46.88%] [count: INV]
  else
    goto <bb 5>; [53.13%] [count: INV]

  <bb 4> [66.00%] [count: INV]:
  c = 0;

  <bb 5> [100.00%] [count: INV]:
The reason why we punt is the unexpected _4 != 1 condition, the code
is prepared to handle just _4 == 0 (or _4 != 0) where _4 == 0 is equivalent
to _4 != 1 for boolean type.

The following patch handles even comparison with 1 if the type is
unsigned 1-bit precision.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2017-08-03  Jakub Jelinek  <ja...@redhat.com>

        PR tree-optimization/81655
        PR tree-optimization/81588
        * tree-ssa-reassoc.c (optimize_range_tests_var_bound): Handle also
        the case when ranges[i].low and high are 1 for unsigned type with
        precision 1.

--- gcc/tree-ssa-reassoc.c.jj   2017-08-01 10:28:50.000000000 +0200
+++ gcc/tree-ssa-reassoc.c      2017-08-02 11:28:44.789134681 +0200
@@ -2918,11 +2918,22 @@ optimize_range_tests_var_bound (enum tre
 
   for (i = 0; i < length; i++)
     {
+      bool in_p = ranges[i].in_p;
       if (ranges[i].low == NULL_TREE
-         || ranges[i].high == NULL_TREE
-         || !integer_zerop (ranges[i].low)
-         || !integer_zerop (ranges[i].high))
+         || ranges[i].high == NULL_TREE)
        continue;
+      if (!integer_zerop (ranges[i].low)
+         || !integer_zerop (ranges[i].high))
+       {
+         if (ranges[i].exp
+             && TYPE_PRECISION (TREE_TYPE (ranges[i].exp)) == 1
+             && TYPE_UNSIGNED (TREE_TYPE (ranges[i].exp))
+             && integer_onep (ranges[i].low)
+             && integer_onep (ranges[i].high))
+           in_p = !in_p;
+         else
+           continue;
+       }
 
       gimple *stmt;
       tree_code ccode;
@@ -2964,7 +2975,7 @@ optimize_range_tests_var_bound (enum tre
        default:
          continue;
        }
-      if (ranges[i].in_p)
+      if (in_p)
        ccode = invert_tree_comparison (ccode, false);
       switch (ccode)
        {

        Jakub