tree-optimization/121756 - handle irreducible regions when sinking

The sinking code currently does not heuristically avoid placing
code into an irreducible region in the same way it avoids placing
into a deeper loop nest.  Critically for the PR we may not insert
a VDEF into a irreducible region that does not contain a virtual
definition.  The following adds the missing heuristic and also
a stop-gap for the VDEF issue - since we cannot determine
validity inside an irreducible region we have to reject any
VDEF movement with destination inside such region, even when
it originates there.  In particular irreducible sub-cycles are
not tracked separately and can cause issues.

I chose to not complicate the already partly incomplete assert
but prune it down to essentials.

	PR tree-optimization/121756
	* tree-ssa-sink.cc (select_best_block): Avoid irreducible
	regions in otherwise same loop depth.
	(statement_sink_location): When sinking a VDEF, never place
	that into an irreducible region.

	* gcc.dg/torture/pr121756.c: New testcase.

2 files changed, 41 insertions, 6 deletions

diff --git a/gcc/testsuite/gcc.dg/torture/pr121756.c b/gcc/testsuite/gcc.dg/torture/pr121756.c
new file mode 100644
index 0000000..37c5c50
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr121756.c
@@ -0,0 +1,30 @@
+/* { dg-do compile } */
+
+int a, b, *c = &b;
+static void g(int i) {
+  int d = 0, e, f[] = {a}, j = a;
+  e = b;
+  if (e - i)
+    return;
+  a = 0;
+h:
+  if (e) {
+    e = j;
+    if (f[3])
+      goto k;
+    goto h;
+  }
+  while (1) {    d = -1;
+    while (1) {
+      if (d - 1 - j < 0)
+        return;
+    k:
+      if (f[1])
+        break;
+    }
+  }
+}
+int main() {
+  g(1);
+  return 0;
+}
diff --git a/gcc/tree-ssa-sink.cc b/gcc/tree-ssa-sink.cc
index 2244e89f..60dfe528 100644
--- a/gcc/tree-ssa-sink.cc
+++ b/gcc/tree-ssa-sink.cc
@@ -245,6 +245,12 @@ select_best_block (basic_block early_bb,
       else if (bb_loop_depth (temp_bb) > bb_loop_depth (best_bb))
 	;
 
+      /* Likewise an irreducible region inside an otherwise same loop
+	 depth.  */
+      else if ((temp_bb->flags & BB_IRREDUCIBLE_LOOP)
+	       && !(best_bb->flags & BB_IRREDUCIBLE_LOOP))
+	;
+
       /* But sink the least distance, if the new candidate on the same
 	 loop depth is post-dominated by the current best block pick
 	 the new candidate.  */
@@ -265,11 +271,7 @@ select_best_block (basic_block early_bb,
     }
 
   gcc_checking_assert (best_bb == early_bb
-		       || (!do_not_sink (stmt, early_bb, best_bb)
-			   && ((bb_loop_depth (best_bb)
-				< bb_loop_depth (early_bb))
-			       || !dominated_by_p (CDI_POST_DOMINATORS,
-						   early_bb, best_bb))));
+		       || !do_not_sink (stmt, early_bb, best_bb));
 
   return best_bb;
 }
@@ -500,7 +502,10 @@ statement_sink_location (gimple *stmt, basic_block frombb,
 	 operand update, requiring inserting of a PHI node.  */
       || (gimple_vdef (stmt)
 	  && bestbb != sinkbb
-	  && !dominated_by_p (CDI_POST_DOMINATORS, bestbb, sinkbb)))
+	  && !dominated_by_p (CDI_POST_DOMINATORS, bestbb, sinkbb))
+      /* Likewise avoid placing VDEFs into an irreducible region.  */
+      || (gimple_vdef (stmt)
+	  && (bestbb->flags & BB_IRREDUCIBLE_LOOP)))
     return false;
 
   *togsi = gsi_after_labels (bestbb);