From: Jason Merrill <jason@redhat.com>
Date: Fri, 19 Jul 2019 08:52:41 +0000 (-0400)
Subject: PR c++/82081 - tail call optimization breaks noexcept
X-Git-Tag: releases/gcc-9.2.0~134
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=19aeedf7af4305455517b87c69681d060f999034;p=thirdparty%2Fgcc.git

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: r273594
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 22716b0c0c0b..af38e8be96a3 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2019-07-19  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.
+
 2019-07-18  Kito Cheng  <kito.cheng@sifive.com>
 
 	Backport from mainline
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
index 000000000000..c67af6e41c72
--- /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 afe8931b5f09..e0265b22dd5f 100644
--- 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);