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.
Tested x86_64-pc-linux-gnu. OK for trunk or hold for GCC 10? This isn't a
regression, but it is a straightforward fix for a wrong-code bug.
* tree-tailcall.c (find_tail_calls): Don't turn a call from a
nothrow function to a might-throw function into a tail call.
---
gcc/tree-tailcall.c | 7 +++++++
gcc/testsuite/g++.dg/tree-ssa/tail-call-1.C | 11 +++++++++++
gcc/ChangeLog | 6 ++++++
3 files changed, 24 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/tree-ssa/tail-call-1.C
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);
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/ChangeLog b/gcc/ChangeLog
index 02d3d07d0e4..77ab20929ff 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2019-04-11 Jason Merrill <ja...@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.
+
2019-04-12 Jakub Jelinek <ja...@redhat.com>
PR rtl-optimization/89965
base-commit: b7a39acf193fd19e41502d5e2cf6b3fa8b44dbac
--
2.20.1
