[PATCH] tree-optimization/96931 - clear ctrl-altering flag more aggressively

[PATCH] tree-optimization/96931 - clear ctrl-altering flag more aggressively

[Richard Biener]

The testcase shows that we fail to clear gimple_call_ctrl_altering_p
when the last abnormal edge goes away, causing an edge insert to
a loop header edge when we have preheaders to split the edge
unnecessarily.

The following addresses this by more aggressively clearing the
flag in cleanup_call_ctrl_altering_flag.

Bootstrapped / tested on x86_64-unknown-linux-gnu, pushed to master.

2020-09-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/96931
	* tree-cfgcleanup.c (cleanup_call_ctrl_altering_flag): If
	there's a fallthru edge and no abnormal edge the call is
	no longer control-altering.
	(cleanup_control_flow_bb): Pass down the BB to
	cleanup_call_ctrl_altering_flag.

	* gcc.dg/pr96931.c: New testcase.
---
 gcc/testsuite/gcc.dg/pr96931.c | 19 +++++++++++++++++++
 gcc/tree-cfgcleanup.c          | 22 ++++++++++++++++++++--
 2 files changed, 39 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr96931.c

diff --git a/gcc/testsuite/gcc.dg/pr96931.c b/gcc/testsuite/gcc.dg/pr96931.c
new file mode 100644
index 00000000000..94b8a1128ee
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr96931.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fpredictive-commoning -fno-tree-loop-im" } */
+
+int bl;
+
+void
+p3 (void);
+
+void __attribute__ ((returns_twice))
+ie (void)
+{
+  p3 ();
+
+  bl = 0;
+  for (;;)
+    ++bl;
+
+  ie ();
+}
diff --git a/gcc/tree-cfgcleanup.c b/gcc/tree-cfgcleanup.c
index 4763cd45a1c..f8169eef781 100644
--- a/gcc/tree-cfgcleanup.c
+++ b/gcc/tree-cfgcleanup.c
@@ -209,7 +209,7 @@ cleanup_control_expr_graph (basic_block bb, gimple_stmt_iterator gsi)
    to updated gimple_call_flags.  */
 
 static void
-cleanup_call_ctrl_altering_flag (gimple *bb_end)
+cleanup_call_ctrl_altering_flag (basic_block bb, gimple *bb_end)
 {
   if (!is_gimple_call (bb_end)
       || !gimple_call_ctrl_altering_p (bb_end))
@@ -220,6 +220,24 @@ cleanup_call_ctrl_altering_flag (gimple *bb_end)
        && !(flags & ECF_LOOPING_CONST_OR_PURE))
       || (flags & ECF_LEAF))
     gimple_call_set_ctrl_altering (bb_end, false);
+  else
+    {
+      edge_iterator ei;
+      edge e;
+      bool found = false;
+      FOR_EACH_EDGE (e, ei, bb->succs)
+	if (e->flags & EDGE_FALLTHRU)
+	  found = true;
+	else if (e->flags & EDGE_ABNORMAL)
+	  {
+	    found = false;
+	    break;
+	  }
+      /* If there's no abnormal edge and a fallthru edge the call
+	 isn't control-altering anymore.  */
+      if (found)
+	gimple_call_set_ctrl_altering (bb_end, false);
+    }
 }
 
 /* Try to remove superfluous control structures in basic block BB.  Returns
@@ -243,7 +261,7 @@ cleanup_control_flow_bb (basic_block bb)
   stmt = gsi_stmt (gsi);
 
   /* Try to cleanup ctrl altering flag for call which ends bb.  */
-  cleanup_call_ctrl_altering_flag (stmt);
+  cleanup_call_ctrl_altering_flag (bb, stmt);
 
   if (gimple_code (stmt) == GIMPLE_COND
       || gimple_code (stmt) == GIMPLE_SWITCH)
-- 
2.26.2