From d407e7f53b4a9c3f607b692d89b4ad7d87df5933 Mon Sep 17 00:00:00 2001 From: Jason Merrill Date: Mon, 29 Apr 2019 13:27:13 -0400 Subject: [PATCH] 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 --- gcc/ChangeLog | 6 ++++++ gcc/testsuite/g++.dg/tree-ssa/tail-call-1.C | 11 +++++++++++ gcc/tree-tailcall.c | 7 +++++++ 3 files changed, 24 insertions(+) create mode 100644 gcc/testsuite/g++.dg/tree-ssa/tail-call-1.C 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 + + 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 * 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); -- 2.30.2