[PATCH] tree-optimization/106722 - fix CD-DCE edge marking

[Richard Biener via Gcc-patches]

The following fixes a latent issue when we mark control edges but
end up with marking a block with no stmts necessary.  In this case
we fail to mark dependent control edges of that block.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Does this look OK?

Thanks,
Richard.

        PR tree-optimization/106722
        * tree-ssa-dce.cc (mark_last_stmt_necessary): Return
        whether we marked a stmt.
        (mark_control_dependent_edges_necessary): When
        mark_last_stmt_necessary didn't mark any stmt make sure
        to mark its control dependent edges.
        (propagate_necessity): Likewise.

        * gcc.dg/torture/pr108737.c: New testcase.
---
 gcc/testsuite/gcc.dg/torture/pr108737.c | 19 +++++++++++++++++++
 gcc/tree-ssa-dce.cc                     | 20 +++++++++++++-------
 2 files changed, 32 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr108737.c

diff --git a/gcc/testsuite/gcc.dg/torture/pr108737.c 
b/gcc/testsuite/gcc.dg/torture/pr108737.c
new file mode 100644
index 00000000000..c8388bcabeb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr108737.c
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+
+extern void exit (int);
+extern void abort (void);
+
+void __attribute__((noipa)) foo () { exit (0); }
+
+void __attribute__((noipa)) blah (int x)
+{
+  while (1) {
+      if(x) foo();
+  }
+}
+
+int main()
+{
+  blah (1);
+  abort ();
+}
diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
index b2fe9f4f55e..21b3294fc86 100644
--- a/gcc/tree-ssa-dce.cc
+++ b/gcc/tree-ssa-dce.cc
@@ -327,17 +327,23 @@ mark_stmt_if_obviously_necessary (gimple *stmt, bool 
aggressive)
 
 /* Mark the last statement of BB as necessary.  */
 
-static void
+static bool
 mark_last_stmt_necessary (basic_block bb)
 {
   gimple *stmt = last_stmt (bb);
 
-  bitmap_set_bit (last_stmt_necessary, bb->index);
+  if (!bitmap_set_bit (last_stmt_necessary, bb->index))
+    return true;
+
   bitmap_set_bit (bb_contains_live_stmts, bb->index);
 
   /* We actually mark the statement only if it is a control statement.  */
   if (stmt && is_ctrl_stmt (stmt))
-    mark_stmt_necessary (stmt, true);
+    {
+      mark_stmt_necessary (stmt, true);
+      return true;
+    }
+  return false;
 }
 
 
@@ -369,8 +375,8 @@ mark_control_dependent_edges_necessary (basic_block bb, 
bool ignore_self)
          continue;
        }
 
-      if (!bitmap_bit_p (last_stmt_necessary, cd_bb->index))
-       mark_last_stmt_necessary (cd_bb);
+      if (!mark_last_stmt_necessary (cd_bb))
+       mark_control_dependent_edges_necessary (cd_bb, false);
     }
 
   if (!skipped)
@@ -790,8 +796,8 @@ propagate_necessity (bool aggressive)
                  if (gimple_bb (stmt)
                      != get_immediate_dominator (CDI_POST_DOMINATORS, arg_bb))
                    {
-                     if (!bitmap_bit_p (last_stmt_necessary, arg_bb->index))
-                       mark_last_stmt_necessary (arg_bb);
+                     if (!mark_last_stmt_necessary (arg_bb))
+                       mark_control_dependent_edges_necessary (arg_bb, false);
                    }
                  else if (arg_bb != ENTRY_BLOCK_PTR_FOR_FN (cfun)
                           && !bitmap_bit_p (visited_control_parents,
-- 
2.35.3