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* [PATCH] c++: Drop TREE_READONLY on vars (possibly) initialized by tls wrapper [PR109164]
@ 2023-03-17 17:51 Jakub Jelinek
  2023-03-18 12:39 ` Jason Merrill
  0 siblings, 1 reply; 8+ messages in thread
From: Jakub Jelinek @ 2023-03-17 17:51 UTC (permalink / raw)
  To: Jason Merrill; +Cc: gcc-patches

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  <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


^ permalink raw reply	[flat|nested] 8+ messages in thread
end of thread, other threads:[~2023-03-20 19:28 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-03-17 17:51 [PATCH] c++: Drop TREE_READONLY on vars (possibly) initialized by tls wrapper [PR109164] Jakub Jelinek
2023-03-18 12:39 ` Jason Merrill
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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