hardcfr: support checking at abnormal edges [PR111943]

Control flow redundancy may choose abnormal edges for early checking,
but that breaks because we can't insert checks on such edges.

Introduce conditional checking on the dest block of abnormal edges,
and leave it for the optimizer to drop the conditional.


for  gcc/ChangeLog

	PR tree-optimization/111943
	* gimple-harden-control-flow.cc: Adjust copyright year.
	(rt_bb_visited): Add vfalse and vtrue data members.
	Zero-initialize them in the ctor.
	(rt_bb_visited::insert_exit_check_on_edge): Upon encountering
	abnormal edges, insert initializers for vfalse and vtrue on
	entry, and insert the check sequence guarded by a conditional
	in the dest block.

for  libgcc/ChangeLog

	* hardcfr.c: Adjust copyright year.

for  gcc/testsuite/ChangeLog

	PR tree-optimization/111943
	* gcc.dg/harden-cfr-pr111943.c: New.

gcc/gimple-harden-control-flow.cc

@@ -1,5 +1,5 @@
 /* Control flow redundancy hardening.
-   Copyright (C) 2022 Free Software Foundation, Inc.
+   Copyright (C) 2022-2023 Free Software Foundation, Inc.
    Contributed by Alexandre Oliva <oliva@adacore.com>.
 
 This file is part of GCC.
@@ -460,6 +460,10 @@ class rt_bb_visited
      at the end of a block's predecessors or successors list.  */
   tree ckfail, ckpart, ckinv, ckblk;
 
+  /* If we need to deal with abnormal edges, we insert SSA_NAMEs for
+     boolean true and false.  */
+  tree vfalse, vtrue;
+
   /* Convert a block index N to a block vindex, the index used to
      identify it in the VISITED array.  Check that it's in range:
      neither ENTRY nor EXIT, but maybe one-past-the-end, to compute
@@ -596,7 +600,8 @@ public:
   /* Prepare to add control flow redundancy testing to CFUN.  */
   rt_bb_visited (int checkpoints)
     : nblocks (n_basic_blocks_for_fn (cfun)),
-      vword_type (NULL), ckseq (NULL), rtcfg (NULL)
+      vword_type (NULL), ckseq (NULL), rtcfg (NULL),
+      vfalse (NULL), vtrue (NULL)
   {
     /* If we've already added a declaration for the builtin checker,
        extract vword_type and vword_bits from its declaration.  */
@@ -703,7 +708,74 @@ public:
   /* Insert SEQ on E.  */
   void insert_exit_check_on_edge (gimple_seq seq, edge e)
   {
-    gsi_insert_seq_on_edge_immediate (e, seq);
+    if (!(e->flags & EDGE_ABNORMAL))
+      {
+	gsi_insert_seq_on_edge_immediate (e, seq);
+	return;
+      }
+
+    /* Initialize SSA boolean constants for use in abnormal PHIs.  */
+    if (!vfalse)
+      {
+	vfalse = make_ssa_name (boolean_type_node);
+	vtrue = make_ssa_name (boolean_type_node);
+
+	gimple_seq vft_seq = NULL;
+	gassign *vfalse_init = gimple_build_assign (vfalse, boolean_false_node);
+	gimple_seq_add_stmt (&vft_seq, vfalse_init);
+	gassign *vtrue_init = gimple_build_assign (vtrue, boolean_true_node);
+	gimple_seq_add_stmt (&vft_seq, vtrue_init);
+
+	gsi_insert_seq_on_edge_immediate (single_succ_edge
+					  (ENTRY_BLOCK_PTR_FOR_FN (cfun)),
+					  vft_seq);
+      }
+
+    /* We can't insert on abnormal edges, but we can arrange for SEQ
+       to execute conditionally at dest.  Add a PHI boolean with TRUE
+       from E and FALSE from other preds, split the whole block, add a
+       test for the PHI to run a new block with SEQ or skip straight
+       to the original block.  If there are multiple incoming abnormal
+       edges, we'll do this multiple times.  ??? Unless there are
+       multiple abnormal edges with different postcheck status, we
+       could split the block and redirect other edges, rearranging the
+       PHI nodes.  Optimizers already know how to do this, so we can
+       keep things simple here.  */
+    basic_block bb = e->dest;
+    basic_block bb_postcheck = split_block_after_labels (bb)->dest;
+
+    basic_block bb_check = create_empty_bb (e->dest);
+    bb_check->count = e->count ();
+    if (dom_info_available_p (CDI_DOMINATORS))
+      set_immediate_dominator (CDI_DOMINATORS, bb_check, bb);
+    if (current_loops)
+      add_bb_to_loop (bb_check, current_loops->tree_root);
+
+    gimple_stmt_iterator chkpt = gsi_after_labels (bb_check);
+    gsi_insert_seq_before_without_update (&chkpt, seq, GSI_SAME_STMT);
+    edge edge_postcheck = make_edge (bb_check, bb_postcheck, EDGE_FALLTHRU);
+    edge_postcheck->probability = profile_probability::always ();
+
+    tree cond_var = make_ssa_name (boolean_type_node);
+    gcond *cond = gimple_build_cond (NE_EXPR, cond_var, boolean_false_node,
+				     NULL, NULL);
+    gimple_stmt_iterator condpt = gsi_after_labels (bb);
+    gsi_insert_before (&condpt, cond, GSI_SAME_STMT);
+    edge edge_nocheck = single_succ_edge (bb);
+    edge_nocheck->flags &= ~EDGE_FALLTHRU;
+    edge_nocheck->flags |= EDGE_FALSE_VALUE;
+    edge edge_check = make_edge (bb, bb_check, EDGE_TRUE_VALUE);
+    edge_check->probability = e->count ().probability_in (bb->count);
+    edge_nocheck->probability = edge_check->probability.invert ();
+
+    gphi *cond_phi = create_phi_node (cond_var, bb);
+    for (int i = 0, ei = EDGE_COUNT (bb->preds); i < ei; i++)
+      {
+	edge pred = EDGE_PRED (bb, i);
+	bool check_edge = pred == e;
+	tree val = check_edge ? vtrue : vfalse;
+	add_phi_arg (cond_phi, val, pred, UNKNOWN_LOCATION);
+      }
   }
 
   /* Add checking code to CHK_EDGES and CHKCALL_BLOCKS, and

gcc/testsuite/gcc.dg/harden-cfr-pr111943.c

@@ -0,0 +1,33 @@
+/* { dg-do compile } */
+/* { dg-options "-fharden-control-flow-redundancy --param=max-jump-thread-duplication-stmts=0 -Ofast -fdump-tree-hardcfr -fdump-tree-optimized" } */
+/* { dg-require-effective-target indirect_jumps } */
+/* { dg-require-effective-target label_values } */
+
+/* Based on gcc.c-torture/compile/20050510-1.c.  */
+
+extern void dont_remove (void);
+
+void bar (int k)
+{
+  void *label = (k) ? &&x : &&y;
+
+  if (k >= 0)
+    goto *label;
+
+x:
+  if (k <= 0)
+    dont_remove ();
+  /* else goto y; */
+
+y:
+  return;
+}
+
+/* Check before calling dont_remove(), in the 'else goto y' edge, and in the
+   abnormal edge to y.  */
+/* { dg-final { scan-tree-dump-times "hardcfr_check" 3 "hardcfr" } } */
+/* { dg-final { scan-tree-dump-times "hardcfr_check" 3 "optimized" } } */
+/* Check that hardcfr introduces an abnormal PHI node (this could be avoided,
+   but it's not worth the effort), and that it gets optimized out.  */
+/* { dg-final { scan-tree-dump-times {\(ab\) = PHI .*\(ab\)} 1 "hardcfr" } } */
+/* { dg-final { scan-tree-dump-not {\(ab\) = PHI .*\(ab\)} "optimized" } } */

libgcc/hardcfr.c

@@ -1,5 +1,5 @@
 /* Control flow redundancy hardening
-   Copyright (C) 2022 Free Software Foundation, Inc.
+   Copyright (C) 2022-2023 Free Software Foundation, Inc.
    Contributed by Alexandre Oliva <oliva@adacore.com>
 
 This file is part of GCC.