PR c++/82081 - tail call optimization breaks noexcept

If a noexcept function calls a function that might throw, doing the tail
call optimization means that an exception thrown in the called function
will propagate out, breaking the noexcept specification.  So we need to
prevent the optimization in that case.

	* tree-tailcall.c (find_tail_calls): Don't turn a call from a
	nothrow function to a might-throw function into a tail call.

From-SVN: r270656

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index e548281a86d571bafee5d81fcdd2d8be9abf2315..b4554f60269d52250367421c43a26f71bb047c1d 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2019-04-29  Jason Merrill  <jason@redhat.com>
+
+       PR c++/82081 - tail call optimization breaks noexcept
+       * tree-tailcall.c (find_tail_calls): Don't turn a call from a
+       nothrow function to a might-throw function into a tail call.
+
 2019-04-29  Richard Sandiford  <richard.sandiford@arm.com>
 
        * tree-data-ref.h (data_dependence_relation::inner_loop): Delete.

diff --git a/gcc/testsuite/g++.dg/tree-ssa/tail-call-1.C b/gcc/testsuite/g++.dg/tree-ssa/tail-call-1.C
new file mode 100644 (file)
index 0000000..c67af6e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/tail-call-1.C
@@ -0,0 +1,11 @@
+// PR c++/82081
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-O2 -fdump-tree-optimized" }
+// { dg-final { scan-tree-dump-not "tail call" "optimized" } }
+
+int g(int) ;
+
+int f() noexcept {
+    int i = 42, j = 43;
+    return g(i+j);
+}

diff --git a/gcc/tree-tailcall.c b/gcc/tree-tailcall.c
index afe8931b5f09e1bd6aa4a1d7d4e755a71240a0ab..e0265b22dd5f85c91a004fbb813ffd89d311a2ec 100644 (file)
--- a/gcc/tree-tailcall.c
+++ b/gcc/tree-tailcall.c
@@ -37,6 +37,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-into-ssa.h"
 #include "tree-dfa.h"
 #include "except.h"
+#include "tree-eh.h"
 #include "dbgcnt.h"
 #include "cfgloop.h"
 #include "common/common-target.h"
@@ -472,6 +473,12 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
       && !auto_var_in_fn_p (ass_var, cfun->decl))
     return;
 
+  /* If the call might throw an exception that wouldn't propagate out of
+     cfun, we can't transform to a tail or sibling call (82081).  */
+  if (stmt_could_throw_p (cfun, stmt)
+      && !stmt_can_throw_external (cfun, stmt))
+    return;
+
   /* We found the call, check whether it is suitable.  */
   tail_recursion = false;
   func = gimple_call_fndecl (call);