[PATCH] sel-sched: fix zero-usefulness case in sel_rank_for_schedule (PR 83513)

[Alexander Monakov]

Hello,

we need the following follow-up fix for priority comparison in
sel_rank_for_schedule as demonstrated by PR 83513.  Checked on
x86_64 by running a bootstrap and also checking for no regressions in
make -k check-gcc 
RUNTESTFLAGS="--target_board=unix/-fselective-scheduling/-fschedule-insns"

OK to apply?

        PR rtl-optimization/83513
        * sel-sched.c (sel_rank_for_schedule): Order by non-zero usefulness
        before priority comparison.

diff --git a/gcc/sel-sched.c b/gcc/sel-sched.c
index c1be0136551..be3813717ba 100644
--- a/gcc/sel-sched.c
+++ b/gcc/sel-sched.c
@@ -3396,17 +3396,22 @@ sel_rank_for_schedule (const void *x, const void *y)
   else if (control_flow_insn_p (tmp2_insn) && !control_flow_insn_p (tmp_insn))
     return 1;

+  /* Prefer an expr with non-zero usefulness.  */
+  int u1 = EXPR_USEFULNESS (tmp), u2 = EXPR_USEFULNESS (tmp2);
+
+  if (u1 == 0)
+    {
+      if (u2 == 0)
+        u1 = u2 = 1;
+      else
+        return 1;
+    }
+  else if (u2 == 0)
+    return -1;
+
   /* Prefer an expr with greater priority.  */
-  if (EXPR_USEFULNESS (tmp) != 0 || EXPR_USEFULNESS (tmp2) != 0)
-    {
-      int p2 = EXPR_PRIORITY (tmp2) + EXPR_PRIORITY_ADJ (tmp2),
-          p1 = EXPR_PRIORITY (tmp) + EXPR_PRIORITY_ADJ (tmp);
-
-      val = p2 * EXPR_USEFULNESS (tmp2) - p1 * EXPR_USEFULNESS (tmp);
-    }
-  else
-    val = EXPR_PRIORITY (tmp2) - EXPR_PRIORITY (tmp)
-         + EXPR_PRIORITY_ADJ (tmp2) - EXPR_PRIORITY_ADJ (tmp);
+  val = (u2 * (EXPR_PRIORITY (tmp2) + EXPR_PRIORITY_ADJ (tmp2))
+         - u1 * (EXPR_PRIORITY (tmp) + EXPR_PRIORITY_ADJ (tmp)));
   if (val)
     return val;