Re: [PATCH][libstc++v3]Add new dg-require-thread-fence directive.

[Renlin Li <renlin dot li at arm dot com>]

Hi Jonathan,

Thank you for the suggestion. I have just attached the updated the 
patch. It works as before.
Is this Okay to commit?

Regards,
Renlin Li

On 22/04/15 11:19, Jonathan Wakely wrote:
> On 21/04/15 15:29 +0100, Renlin Li wrote:
> > Hi all,
> >
> > This patch defines a new dg-require-thread-fence directive. And three
> > test cases are updated to use it.
> >
> > The new directive are used to check whether the target support thread
> > fence either by the target back-end or external library function call.
> > A thread fence is required to expand atomic load/store.
> >
> > There is a case that a call to some external __sync_synchronize will
> > be emitted, and it's not implemented. You will get linking errors like
> > this: undefined reference to `__sync_synchronize`. Test cases which
> > are gated by this directive will be skipped if no thread fence is
> > available. For example the three test cases updated here. They fail on
> > arm-none-eabi target where __sync_synchronize() isn't implemented and
> > target cpu has no memory_barrier.
> >
> > ___sync_synchronize () is used to check whether thread-fence is
> > available. In GCC sync_synchronize is expanded as
> > expand_mem_thread_fence (MEMMODEL_SEQ_CST).
> I don't like making the directive depend directly on the legacy
> __sync_synchronize function, because that function is not required on
> most targets, AFAICT it's only needed for ARM and MIPS.
>
> Could you make the directive check
> __atomic_thread_fence(__ATOMIC_SEQ_CST) instead? I think that will
> still expand to __sync_synchronize() for ARM, so should still test the
> same thing, but that way we aren't adding a dependency on
> __sync_synchronize for all targets.
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_flag/clear/1.cc b/libstdc++-v3/testsuite/29_atomics/atomic_flag/clear/1.cc
index 0a4219c..a6e2299 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_flag/clear/1.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/clear/1.cc
@@ -1,4 +1,5 @@
 // { dg-options "-std=gnu++11" }
+// { dg-require-thread-fence "" }
 
 // Copyright (C) 2009-2015 Free Software Foundation, Inc.
 //
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test_and_set/explicit.cc b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test_and_set/explicit.cc
index 2ff740b..0655be4 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test_and_set/explicit.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test_and_set/explicit.cc
@@ -1,4 +1,5 @@
 // { dg-options "-std=gnu++11" }
+// { dg-require-thread-fence "" }
 
 // Copyright (C) 2008-2015 Free Software Foundation, Inc.
 //
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test_and_set/implicit.cc b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test_and_set/implicit.cc
index 6ac20c0..a867da2 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test_and_set/implicit.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test_and_set/implicit.cc
@@ -1,4 +1,5 @@
 // { dg-options "-std=gnu++11" }
+// { dg-require-thread-fence "" }
 
 // Copyright (C) 2008-2015 Free Software Foundation, Inc.
 //
diff --git a/libstdc++-v3/testsuite/lib/dg-options.exp b/libstdc++-v3/testsuite/lib/dg-options.exp
index 38c8206..56ca896 100644
--- a/libstdc++-v3/testsuite/lib/dg-options.exp
+++ b/libstdc++-v3/testsuite/lib/dg-options.exp
@@ -115,6 +115,15 @@ proc dg-require-cmath { args } {
     return
 }
 
+proc dg-require-thread-fence { args } {
+    if { ![ check_v3_target_thread_fence ] } {
+	upvar dg-do-what dg-do-what
+	set dg-do-what [list [lindex ${dg-do-what} 0] "N" "P"]
+	return
+    }
+    return
+}
+
 proc dg-require-atomic-builtins { args } {
     if { ![ check_v3_target_atomic_builtins ] } {
 	upvar dg-do-what dg-do-what
diff --git a/libstdc++-v3/testsuite/lib/libstdc++.exp b/libstdc++-v3/testsuite/lib/libstdc++.exp
index b2f7d00..9e395e2 100644
--- a/libstdc++-v3/testsuite/lib/libstdc++.exp
+++ b/libstdc++-v3/testsuite/lib/libstdc++.exp
@@ -1221,6 +1221,62 @@ proc check_v3_target_cmath { } {
     return $et_c99_math
 }
 
+proc check_v3_target_thread_fence { } {
+    global cxxflags
+    global DEFAULT_CXXFLAGS
+    global et_thread_fence
+
+    global tool
+
+    if { ![info exists et_thread_fence_target_name] } {
+	set et_thread_fence_target_name ""
+    }
+
+    # If the target has changed since we set the cached value, clear it.
+    set current_target [current_target_name]
+    if { $current_target != $et_thread_fence_target_name } {
+	verbose "check_v3_target_thread_fence: `$et_thread_fence_target_name'" 2
+	set et_thread_fence_target_name $current_target
+	if [info exists et_thread_fence] {
+	    verbose "check_v3_target_thread_fence: removing cached result" 2
+	    unset et_thread_fence
+	}
+    }
+
+    if [info exists et_thread_fence] {
+	verbose "check_v3_target_thread_fence: using cached result" 2
+    } else {
+	set et_thread_fence 0
+
+	# Set up and preprocess a C++11 test program that depends
+	# on the thread fence to be available.
+	set src thread_fence[pid].cc
+
+	set f [open $src "w"]
+	puts $f "int main() {"
+	puts $f "__atomic_thread_fence (__ATOMIC_SEQ_CST);"
+	puts $f "return 0;"
+	puts $f "}"
+	close $f
+
+	set cxxflags_saved $cxxflags
+	set cxxflags "$cxxflags $DEFAULT_CXXFLAGS -Werror -std=gnu++11"
+
+	set lines [v3_target_compile $src /dev/null executable ""]
+	set cxxflags $cxxflags_saved
+	file delete $src
+
+	if [string match "" $lines] {
+	    # No error message, linking succeeded.
+	    set et_thread_fence 1
+	} else {
+	    verbose "check_v3_target_thread_fence: compilation failed" 2
+	}
+    }
+    verbose "check_v3_target_thread_fence: $et_thread_fence" 2
+    return $et_thread_fence
+}
+
 proc check_v3_target_atomic_builtins { } {
     global cxxflags
     global DEFAULT_CXXFLAGS