PR target/82158

	* tree-cfg.c (pass_warn_function_return::execute): In noreturn
	functions when optimizing replace GIMPLE_RETURN stmts with
	calls to __builtin_unreachable ().

	* gcc.dg/tree-ssa/noreturn-1.c: New test.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@253926 138bc75d-0d04-0410-961f-82ee72b054a4

4 files changed, 68 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f28e70a3776..42d98733299 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,10 @@
 2017-10-20  Jakub Jelinek  <jakub@redhat.com>
 
+	PR target/82158
+	* tree-cfg.c (pass_warn_function_return::execute): In noreturn
+	functions when optimizing replace GIMPLE_RETURN stmts with
+	calls to __builtin_unreachable ().
+
 	PR sanitizer/82595
 	* config/gnu-user.h (LIBTSAN_EARLY_SPEC): Add libtsan_preinit.o
 	for -fsanitize=thread link of executables.
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index d3b3be3699d..35cc34e6cb2 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2017-10-20  Jakub Jelinek  <jakub@redhat.com>
 
+	PR target/82158
+	* gcc.dg/tree-ssa/noreturn-1.c: New test.
+
 	PR target/82370
 	* gcc.target/i386/avx-pr82370.c: New test.
 	* gcc.target/i386/avx2-pr82370.c: New test.
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/noreturn-1.c b/gcc/testsuite/gcc.dg/tree-ssa/noreturn-1.c
new file mode 100644
index 00000000000..ae7ee42fabc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/noreturn-1.c
@@ -0,0 +1,42 @@
+/* { dg-do compile } *
+/* { dg-options "-O2 -fdump-tree-ssa -std=gnu11" } */
+/* { dg-final { scan-tree-dump-times "__builtin_unreachable" 4 "ssa" } } */
+
+void bar1 (void);
+void bar2 (void);
+void bar3 (void);
+void bar4 (void);
+
+_Noreturn void
+foo1 (int *p, int y)
+{
+  bar1 ();
+  *p = y;
+  return;	/* { dg-warning "function declared 'noreturn' has a 'return' statement" } */
+}		/* { dg-warning "'noreturn' function does return" "" { target *-*-* } .-1 } */
+
+_Noreturn void
+foo2 (int *p, int y)
+{
+  bar2 ();
+  *p = y;
+}		/* { dg-warning "'noreturn' function does return" } */
+
+_Noreturn void
+foo3 (int *p, int y)
+{
+  if (y > 10)
+    return;	/* { dg-warning "function declared 'noreturn' has a 'return' statement" } */
+  bar3 ();
+  *p = y;
+  return;	/* { dg-warning "function declared 'noreturn' has a 'return' statement" } */
+}		/* { dg-warning "'noreturn' function does return" } */
+
+_Noreturn void
+foo4 (int *p, int y)
+{
+  if (y > 10)
+    return;	/* { dg-warning "function declared 'noreturn' has a 'return' statement" } */
+  bar4 ();
+  *p = y;
+}		/* { dg-warning "'noreturn' function does return" } */
diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index a7c7348ed29..ae1cdb33f53 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -9077,13 +9077,29 @@ pass_warn_function_return::execute (function *fun)
       && EDGE_COUNT (EXIT_BLOCK_PTR_FOR_FN (fun)->preds) > 0)
     {
       location = UNKNOWN_LOCATION;
-      FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR_FOR_FN (fun)->preds)
+      for (ei = ei_start (EXIT_BLOCK_PTR_FOR_FN (fun)->preds);
+	   (e = ei_safe_edge (ei)); )
 	{
 	  last = last_stmt (e->src);
 	  if ((gimple_code (last) == GIMPLE_RETURN
 	       || gimple_call_builtin_p (last, BUILT_IN_RETURN))
-	      && (location = gimple_location (last)) != UNKNOWN_LOCATION)
+	      && location == UNKNOWN_LOCATION
+	      && (location = gimple_location (last)) != UNKNOWN_LOCATION
+	      && !optimize)
 	    break;
+	  /* When optimizing, replace return stmts in noreturn functions
+	     with __builtin_unreachable () call.  */
+	  if (optimize && gimple_code (last) == GIMPLE_RETURN)
+	    {
+	      tree fndecl = builtin_decl_implicit (BUILT_IN_UNREACHABLE);
+	      gimple *new_stmt = gimple_build_call (fndecl, 0);
+	      gimple_set_location (new_stmt, gimple_location (last));
+	      gimple_stmt_iterator gsi = gsi_for_stmt (last);
+	      gsi_replace (&gsi, new_stmt, true);
+	      remove_edge (e);
+	    }
+	  else
+	    ei_next (&ei);
 	}
       if (location == UNKNOWN_LOCATION)
 	location = cfun->function_end_locus;