[PATCH] phiopt: Adjust instead of reset phires range

[Jakub Jelinek via Gcc-patches]

On Thu, Dec 22, 2022 at 01:09:21PM +0100, Aldy Hernandez wrote:
>  INTEGER_CST singleton and
> > union that into the SSA_NAMEs range and then do set_range_info
> > with the altered range I guess.
> >
> 
> Note that set_range_info is an intersect operation. It should really be
> called update_range_info. Up to now, there were no users that wanted to
> clobber old ranges completely.

Thanks.
That would be then (I've committed the previous patch, also for reasons of
backporting) following incremental patch.

For the just committed testcase, it does the right thing,
# RANGE [irange] int [-INF, -1][1, +INF]
# iftmp.2_9 = PHI <iftmp.3_10(4), 8(5)>
is before the range (using -fdump-tree-all-alias) and r below is
[irange] int [-INF, -1][1, +INF],
unioned with carg of 0 into VARYING.
If I try attached testcase though (which just uses signed char d instead of
int d to give more interesting range info), then I see:
# RANGE [irange] int [-128, -1][1, 127]
# iftmp.2_10 = PHI <iftmp.3_11(4), 8(5)>
but strangely r I get from range_of_expr is
[irange] int [-128, 127]
rather than the expected [irange] int [-128, -1][1, 127].
Sure, it is later unioned with 0, so it doesn't change anything, but I
wonder what is the difference.  Note, this is before actually replacing
the phi arg 8(5) with iftmp.3_11(5).
At that point bb4 is:
<bb 4> [local count: 966367640]:
# RANGE [irange] int [-128, 127]
# iftmp.3_11 = PHI <iftmp.3_15(3), 0(2)>
if (iftmp.3_11 != 0)
  goto <bb 6>; [56.25%]
else
  goto <bb 5>; [43.75%]
and bb 5 is empty forwarder, so [-128, -1][1, 127] is actually correct.
Either iftmp.3_11 is non-zero, then iftmp.2_10 is that value and its range, or
it is zero and then iftmp.2_10 is 8, so [-128, -1][1, 127] U [8, 8], but
more importantly SSA_NAME_RANGE_INFO should be at least according to what
is printed be without 0.

2022-12-22  Jakub Jelinek  <ja...@redhat.com>
            Aldy Hernandez  <al...@redhat.com>

        * tree-ssa-phiopt.cc (value_replacement): Instead of resetting
        phires range info, union it with oarg.

--- gcc/tree-ssa-phiopt.cc.jj   2022-12-22 12:52:36.588469821 +0100
+++ gcc/tree-ssa-phiopt.cc      2022-12-22 13:11:51.145060050 +0100
@@ -1492,11 +1492,25 @@ value_replacement (basic_block cond_bb, basic_block 
middle_bb,
                    break;
                  }
              if (equal_p)
-               /* After the optimization PHI result can have value
-                  which it couldn't have previously.
-                  We could instead of resetting it union the range
-                  info with oarg.  */
-               reset_flow_sensitive_info (gimple_phi_result (phi));
+               {
+                 tree phires = gimple_phi_result (phi);
+                 if (SSA_NAME_RANGE_INFO (phires))
+                   {
+                     /* After the optimization PHI result can have value
+                        which it couldn't have previously.  */
+                     value_range r;
+                     if (get_global_range_query ()->range_of_expr (r, phires,
+                                                                   phi))
+                       {
+                         int_range<2> tmp (carg, carg);
+                         r.union_ (tmp);
+                         reset_flow_sensitive_info (phires);
+                         set_range_info (phires, r);
+                       }
+                     else
+                       reset_flow_sensitive_info (phires);
+                   }
+               }
              if (equal_p && MAY_HAVE_DEBUG_BIND_STMTS)
                {
                  imm_use_iterator imm_iter;


        Jakub

// PR tree-optimization/108166
// { dg-do run }

bool a, b;
signed char d;
int c;

const int &
foo (const int &f, const int &g)
{
  return !f ? f : g;
}

__attribute__((noipa)) void
bar (int)
{
}

int
main ()
{
  c = foo (b, 0) > ((b ? d : b) ?: 8);
  a = b ? d : b;
  bar (a);
  if (a != 0)
    __builtin_abort ();
}