From: Jason Merrill <jason@redhat.com>
Date: Mon, 29 Apr 2019 17:27:13 +0000 (-0400)
Subject: PR c++/82081 - tail call optimization breaks noexcept
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=d407e7f53b4a9c3f607b692d89b4ad7d87df5933;p=gcc.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: r270656
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index e548281a86d..b4554f60269 100644
--- 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
index 00000000000..c67af6e41c7
--- /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 afe8931b5f0..e0265b22dd5 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);