Re: [PATCH] c++: Drop TREE_READONLY on vars (possibly) initialized by tls wrapper [PR109164]
On Sat, Mar 18, 2023 at 08:39:45AM -0400, Jason Merrill wrote:
> On 3/17/23 13:51, Jakub Jelinek wrote:
> > 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
The patch is mostly about DECL_EXTERNAL cases, the others are supposedly
handled by the var_definition_p code there (or at least I assumed;
testcases certainly test only DECL_EXTERNAL).
I guess it could be done in cp_finish_decl, maybe better next to the
/* A reference will be modified here, as it is initialized. */
if (! DECL_EXTERNAL (decl)
&& TREE_READONLY (decl)
&& TYPE_REF_P (type))
{
was_readonly = 1;
TREE_READONLY (decl) = 0;
}
spot, but we'd need to export the decl2.cc helpers for it,
because not all DECL_THREAD_LOCAL_P vars need to be treated that way.
if (VAR_P (decl)
&& CP_DECL_THREAD_LOCAL_P (decl)
&& var_needs_tls_wrapper (decl)
&& (!DECL_EXTERNAL (decl) || flag_extern_tls_init))
TREE_READONLY (decl) = 0;
where var_needs_tls_wrapper would need to be exported from decl2.cc.
Though, var_needs_tls_wrapper -> var_defined_without_dynamic_init
needs
DECL_NONTRIVIALLY_INITIALIZED_P/DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P,
so perhaps that is accurate only closer to the end of cp_finish_decl?
Jakub
Re: [PATCH] c++: Drop TREE_READONLY on vars (possibly) initialized by tls wrapper [PR109164]
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
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.jj2023-03-17
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.jj2023-03-17
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
[PATCH] c++: Drop TREE_READONLY on vars (possibly) initialized by tls wrapper [PR109164]
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. 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
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.jj2023-03-17
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.jj2023-03-17
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
