[1/4][PATCH] Fix PR84032

Roman Zhuykov zhroma@ispras.ru
Tue Apr 16 12:03:00 GMT 2019


There is the following mistake in logic behind the code.

We want to schedule the branch instructions only as a last instruction 
in a row. But when branch was scheduled and we add other instructions 
into partial schedule, we sometimes allow them to be in same row after 
the branch.

The issue happens later when we try to reschedule branch into another 
row, algorithm there works like this:
(1) Remove branch from the row where it is (say, “previous row”)
(2) Try insert into the needed row
(3) If success – OK, continue scheduling other instructions
(4) But when inserting (2) was not done – insert it back into “previous 
row” and this insertion must be certainly successful, which is checked 
by assertion.

But when on step (1) branch in not last in a row there is no guarantee, 
that on step (4) we could insert it back, because there we will try only 
last-in-a-row position for it.

This patch solves this totally preventing other instructions to be 
scheduled after branch in the same row.

I’ve described patch testing in cover letter. Ok for trunk?

gcc/ChangeLog:

2019-04-09  Roman Zhuykov  <zhroma@ispras.ru>

	PR rtl-optimization/84032
	* modulo-sched.c (ps_insn_find_column): Change condition so that
	branch will always be the last insn in a row inside partial schedule.

gcc/testsuite/ChangeLog:

2019-04-09  Roman Zhuykov  <zhroma@ispras.ru>

	PR rtl-optimization/84032
	* gcc.dg/pr84032.c: New test.


diff --git a/gcc/modulo-sched.c b/gcc/modulo-sched.c
--- a/gcc/modulo-sched.c
+++ b/gcc/modulo-sched.c
@@ -2996,9 +2996,7 @@ ps_insn_find_column (partial_schedule_ptr ps, 
ps_insn_ptr ps_i,
              last_must_precede = next_ps_i;
          }
        /* The closing branch must be the last in the row.  */
-      if (must_precede
-	  && bitmap_bit_p (must_precede, next_ps_i->id)
-	  && JUMP_P (ps_rtl_insn (ps, next_ps_i->id)))
+      if (JUMP_P (ps_rtl_insn (ps, next_ps_i->id)))
  	return false;

         last_in_row = next_ps_i;
diff --git a/gcc/testsuite/gcc.dg/pr84032.c 
b/gcc/testsuite/gcc.dg/pr84032.c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr84032.c
@@ -0,0 +1,23 @@
+/* PR rtl-optimization/84032 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fmodulo-sched" } */
+/* { dg-additional-options "-mcpu=power6" { target { powerpc-*-* } } } 
*/
+
+void
+yr (int cm)
+{
+  int ka = cm;
+
+  for (;;)
+    {
+      short int m0;
+
+      for (m0 = 0; m0 < 6; ++m0)
+        {
+          ka &= 1;
+          cm *= 2;
+        }
+
+      ka = (ka == 0) ? cm : 0;
+    }
+}



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