From: Jason Merrill <jason@redhat.com>
To: Jakub Jelinek <jakub@redhat.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] c++: Drop TREE_READONLY on vars (possibly) initialized by tls wrapper [PR109164]
Date: Sat, 18 Mar 2023 08:39:45 -0400 [thread overview]
Message-ID: <d949596f-293c-60d7-18d3-7cf308926e58@redhat.com> (raw)
In-Reply-To: <ZBSoqOLhNMhm4YTo@tucnak>
On 3/17/23 13:51, Jakub Jelinek wrote:
> Hi!
>
> The following two testcases are miscompiled, because we keep TREE_READONLY
> on the vars even when they are (possibly) dynamically initialized by a TLS
> wrapper function. Normally cp_finish_decl drops TREE_READONLY from vars
> which need dynamic initialization, but for TLS we do this kind of
> initialization upon every access to those variables.
Why not handle this case in cp_finish_decl, too? That is, add
DECL_THREAD_LOCAL_P to the TREE_STATIC check in
> if (var_definition_p
> /* With -fmerge-all-constants, gimplify_init_constructor
> might add TREE_STATIC to aggregate variables. */
> && (TREE_STATIC (decl)
> || (flag_merge_constants >= 2
> && AGGREGATE_TYPE_P (type))))
> {
> /* If a TREE_READONLY variable needs initialization
> at runtime, it is no longer readonly and we need to
> avoid MEM_READONLY_P being set on RTL created for it. */
?
> Keeping them
> TREE_READONLY means e.g. PRE can hoist loads from those before loops
> which contain the TLS wrapper calls, so we can access the TLS variables
> before they are initialized.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2023-03-17 Jakub Jelinek <jakub@redhat.com>
>
> PR c++/109164
> * decl2.cc (get_tls_wrapper_fn): Clear TREE_READONLY on variables for
> which a TLS wrapper is added.
>
> * g++.dg/tls/thread_local13.C: New test.
> * g++.dg/tls/thread_local13-aux.cc: New file.
> * g++.dg/tls/thread_local14.C: New test.
> * g++.dg/tls/thread_local14-aux.cc: New file.
>
> --- gcc/cp/decl2.cc.jj 2023-03-07 21:20:31.800491531 +0100
> +++ gcc/cp/decl2.cc 2023-03-17 12:20:11.960678291 +0100
> @@ -3773,6 +3773,12 @@ get_tls_wrapper_fn (tree var)
> DECL_BEFRIENDING_CLASSES (fn) = var;
>
> set_global_binding (fn);
> +
> + /* The variable now needs dynamic initialization by the wrapper
> + function, we don't want to hoist accesses to it before the
> + wrapper. */
> + if (TREE_READONLY (var))
> + TREE_READONLY (var) = 0;
> }
> return fn;
> }
> --- gcc/testsuite/g++.dg/tls/thread_local13.C.jj 2023-03-17 12:28:24.692427351 +0100
> +++ gcc/testsuite/g++.dg/tls/thread_local13.C 2023-03-17 12:30:34.505519746 +0100
> @@ -0,0 +1,21 @@
> +// PR c++/109164
> +// { dg-do run { target c++11 } }
> +// { dg-options "-O2" }
> +// { dg-add-options tls }
> +// { dg-require-effective-target tls_runtime }
> +// { dg-additional-sources "thread_local13-aux.cc" }
> +
> +struct S { virtual void foo (); int s; };
> +extern thread_local S &t;
> +bool bar ();
> +
> +bool
> +baz ()
> +{
> + while (1)
> + {
> + t.foo ();
> + if (!bar ())
> + return false;
> + }
> +}
> --- gcc/testsuite/g++.dg/tls/thread_local13-aux.cc.jj 2023-03-17 12:28:28.721368058 +0100
> +++ gcc/testsuite/g++.dg/tls/thread_local13-aux.cc 2023-03-17 12:37:53.952070861 +0100
> @@ -0,0 +1,35 @@
> +// PR c++/109164
> +
> +struct S { virtual void foo (); int s; };
> +extern bool baz ();
> +
> +void
> +S::foo ()
> +{
> + if (s != 42)
> + __builtin_abort ();
> +}
> +
> +S s;
> +
> +S &
> +qux ()
> +{
> + s.s = 42;
> + return s;
> +}
> +
> +thread_local S &t = qux ();
> +
> +bool
> +bar ()
> +{
> + return false;
> +}
> +
> +int
> +main ()
> +{
> + if (baz ())
> + __builtin_abort ();
> +}
> --- gcc/testsuite/g++.dg/tls/thread_local14.C.jj 2023-03-17 12:35:48.951905245 +0100
> +++ gcc/testsuite/g++.dg/tls/thread_local14.C 2023-03-17 12:49:03.456249628 +0100
> @@ -0,0 +1,19 @@
> +// PR c++/109164
> +// { dg-do run { target c++11 } }
> +// { dg-options "-O2" }
> +// { dg-add-options tls }
> +// { dg-require-effective-target tls_runtime }
> +// { dg-additional-sources "thread_local14-aux.cc" }
> +
> +extern thread_local const int t;
> +bool bar (int);
> +
> +bool
> +baz ()
> +{
> + while (1)
> + {
> + if (!bar (t))
> + return false;
> + }
> +}
> --- gcc/testsuite/g++.dg/tls/thread_local14-aux.cc.jj 2023-03-17 12:36:58.724881322 +0100
> +++ gcc/testsuite/g++.dg/tls/thread_local14-aux.cc 2023-03-17 12:48:53.914389421 +0100
> @@ -0,0 +1,26 @@
> +// PR c++/109164
> +
> +extern bool baz ();
> +
> +int
> +qux ()
> +{
> + return 42;
> +}
> +
> +extern thread_local const int t = qux ();
> +
> +bool
> +bar (int x)
> +{
> + if (x != 42)
> + __builtin_abort ();
> + return false;
> +}
> +
> +int
> +main ()
> +{
> + if (baz ())
> + __builtin_abort ();
> +}
>
> Jakub
>
next prev parent reply other threads:[~2023-03-18 12:39 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-17 17:51 Jakub Jelinek
2023-03-18 12:39 ` Jason Merrill [this message]
2023-03-18 12:54 ` Jakub Jelinek
2023-03-18 15:09 ` [PATCH] c++, v2: " Jakub Jelinek
2023-03-20 15:45 ` Jakub Jelinek
2023-03-20 19:15 ` Jason Merrill
2023-03-20 19:26 ` Jakub Jelinek
2023-03-20 19:28 ` Jason Merrill
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