[PATCH v2] combine: perform jump threading at the end

[Ilya Leoshkevich]

gcc/ChangeLog:

2018-09-05  Ilya Leoshkevich  <i...@linux.ibm.com>

        PR target/80080
        * combine.c (rest_of_handle_combine): Perform jump threading.

gcc/testsuite/ChangeLog:

2018-09-05  Ilya Leoshkevich  <i...@linux.ibm.com>

        PR target/80080
        * gcc.target/s390/pr80080-4.c: New test.
---
 gcc/combine.c                             | 10 ++++++++--
 gcc/testsuite/gcc.target/s390/pr80080-4.c | 16 ++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/s390/pr80080-4.c

diff --git a/gcc/combine.c b/gcc/combine.c
index a2649b6d5a1..818b4c5b77d 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -14960,10 +14960,16 @@ rest_of_handle_combine (void)
        free_dominance_info (CDI_DOMINATORS);
       timevar_push (TV_JUMP);
       rebuild_jump_labels (get_insns ());
-      cleanup_cfg (0);
-      timevar_pop (TV_JUMP);
     }
 
+  /* Combining insns can change basic blocks in a way that they end up
+     containing a single jump_insn. This creates an opportunity to improve code
+     with jump threading.  */
+  cleanup_cfg (CLEANUP_THREADING);
+
+  if (rebuild_jump_labels_after_combine)
+    timevar_pop (TV_JUMP);
+
   regstat_free_n_sets_and_refs ();
   return 0;
 }
diff --git a/gcc/testsuite/gcc.target/s390/pr80080-4.c 
b/gcc/testsuite/gcc.target/s390/pr80080-4.c
new file mode 100644
index 00000000000..91d31ec7845
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/pr80080-4.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-march=z196 -O2" } */
+
+extern void bar(int *mem);
+
+void foo4(int *mem)
+{
+  int oldval = 0;
+  if (!__atomic_compare_exchange_n (mem, (void *) &oldval, 1,
+                                   1, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED))
+    {
+      bar (mem);
+    }
+}
+
+/* { dg-final { scan-assembler 
"\n\tlt\t.*\n\tjne\t(\\.L\\d+)\n(.*\n)*\tcs\t.*\n\tber\t%r14\n\\1:\n\tjg\tbar\n"
 } } */
-- 
2.18.0