[C++11] Replace LLVM atomics with std::atomic.

With C++11 we finally have a standardized way to specify atomic operations. Use
them to replace the existing custom implemention. Sadly the translation is not
entirely trivial as std::atomic allows more fine-grained control over the
atomicity. I tried to preserve the old semantics as well as possible.

Differential Revision: http://llvm-reviews.chandlerc.com/D2915

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202730 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/Statistic.h

@@ -26,8 +26,8 @@
 #ifndef LLVM_ADT_STATISTIC_H
 #define LLVM_ADT_STATISTIC_H
 
-#include "llvm/Support/Atomic.h"
 #include "llvm/Support/Valgrind.h"
+#include <atomic>
 
 namespace llvm {
 class raw_ostream;
@@ -36,10 +36,10 @@ class Statistic {
 public:
   const char *Name;
   const char *Desc;
-  volatile llvm::sys::cas_flag Value;
+  std::atomic<unsigned> Value;
   bool Initialized;
 
-  llvm::sys::cas_flag getValue() const { return Value; }
+  unsigned getValue() const { return Value; }
   const char *getName() const { return Name; }
   const char *getDesc() const { return Desc; }
 
@@ -63,48 +63,54 @@ public:
     // atomic operation to update the value safely in the presence of
     // concurrent accesses, but not to read the return value, so the
     // return value is not thread safe.
-    sys::AtomicIncrement(&Value);
+    ++Value;
     return init();
   }
 
   unsigned operator++(int) {
     init();
-    unsigned OldValue = Value;
-    sys::AtomicIncrement(&Value);
+    unsigned OldValue = Value++;
     return OldValue;
   }
 
   const Statistic &operator--() {
-    sys::AtomicDecrement(&Value);
+    --Value;
     return init();
   }
 
   unsigned operator--(int) {
     init();
-    unsigned OldValue = Value;
-    sys::AtomicDecrement(&Value);
+    unsigned OldValue = Value--;
     return OldValue;
   }
 
   const Statistic &operator+=(const unsigned &V) {
     if (!V) return *this;
-    sys::AtomicAdd(&Value, V);
+    Value += V;
     return init();
   }
 
   const Statistic &operator-=(const unsigned &V) {
     if (!V) return *this;
-    sys::AtomicAdd(&Value, -V);
+    Value -= V;
     return init();
   }
 
   const Statistic &operator*=(const unsigned &V) {
-    sys::AtomicMul(&Value, V);
+    unsigned Original, Result;
+    do {
+      Original = Value;
+      Result = Original * V;
+    } while (!Value.compare_exchange_strong(Original, Result));
     return init();
   }
 
   const Statistic &operator/=(const unsigned &V) {
-    sys::AtomicDiv(&Value, V);
+    unsigned Original, Result;
+    do {
+      Original = Value;
+      Result = Original / V;
+    } while (!Value.compare_exchange_strong(Original, Result));
     return init();
   }
 
@@ -151,7 +157,7 @@ public:
 protected:
   Statistic &init() {
     bool tmp = Initialized;
-    sys::MemoryFence();
+    std::atomic_thread_fence(std::memory_order_seq_cst);
     if (!tmp) RegisterStatistic();
     TsanHappensAfter(this);
     return *this;
@@ -162,7 +168,7 @@ protected:
 // STATISTIC - A macro to make definition of statistics really simple.  This
 // automatically passes the DEBUG_TYPE of the file into the statistic.
 #define STATISTIC(VARNAME, DESC) \
-  static llvm::Statistic VARNAME = { DEBUG_TYPE, DESC, 0, 0 }
+  static llvm::Statistic VARNAME = { DEBUG_TYPE, DESC, {}, 0 }
 
 /// \brief Enable the collection and printing of statistics.
 void EnableStatistics();

include/llvm/PassSupport.h

@@ -24,8 +24,8 @@
 #include "Pass.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/PassRegistry.h"
-#include "llvm/Support/Atomic.h"
 #include "llvm/Support/Valgrind.h"
+#include <atomic>
 #include <vector>
 
 namespace llvm {
@@ -147,21 +147,21 @@ private:
 };
 
 #define CALL_ONCE_INITIALIZATION(function) \
-  static volatile sys::cas_flag initialized = 0; \
-  sys::cas_flag old_val = sys::CompareAndSwap(&initialized, 1, 0); \
-  if (old_val == 0) { \
+  static std::atomic<int> initialized; \
+  int old_val = 0; \
+  if (initialized.compare_exchange_strong(old_val, 1)) { \
     function(Registry); \
-    sys::MemoryFence(); \
+    std::atomic_thread_fence(std::memory_order_seq_cst); \
     TsanIgnoreWritesBegin(); \
     TsanHappensBefore(&initialized); \
     initialized = 2; \
     TsanIgnoreWritesEnd(); \
   } else { \
-    sys::cas_flag tmp = initialized; \
-    sys::MemoryFence(); \
+    int tmp = initialized.load(); \
+    std::atomic_thread_fence(std::memory_order_seq_cst); \
     while (tmp != 2) { \
-      tmp = initialized; \
-      sys::MemoryFence(); \
+      tmp = initialized.load(); \
+      std::atomic_thread_fence(std::memory_order_seq_cst); \
     } \
   } \
   TsanHappensAfter(&initialized);

include/llvm/Support/ManagedStatic.h

@@ -14,9 +14,9 @@
 #ifndef LLVM_SUPPORT_MANAGED_STATIC_H
 #define LLVM_SUPPORT_MANAGED_STATIC_H
 
-#include "llvm/Support/Atomic.h"
 #include "llvm/Support/Threading.h"
 #include "llvm/Support/Valgrind.h"
+#include <atomic>
 
 namespace llvm {
 
@@ -64,7 +64,8 @@ public:
   // Accessors.
   C &operator*() {
     void* tmp = Ptr;
-    if (llvm_is_multithreaded()) sys::MemoryFence();
+    if (llvm_is_multithreaded())
+      std::atomic_thread_fence(std::memory_order_seq_cst);
     if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>::call);
     TsanHappensAfter(this);
 
@@ -72,7 +73,8 @@ public:
   }
   C *operator->() {
     void* tmp = Ptr;
-    if (llvm_is_multithreaded()) sys::MemoryFence();
+    if (llvm_is_multithreaded())
+      std::atomic_thread_fence(std::memory_order_seq_cst);
     if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>::call);
     TsanHappensAfter(this);
 
@@ -80,7 +82,8 @@ public:
   }
   const C &operator*() const {
     void* tmp = Ptr;
-    if (llvm_is_multithreaded()) sys::MemoryFence();
+    if (llvm_is_multithreaded())
+      std::atomic_thread_fence(std::memory_order_seq_cst);
     if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>::call);
     TsanHappensAfter(this);
 
@@ -88,7 +91,8 @@ public:
   }
   const C *operator->() const {
     void* tmp = Ptr;
-    if (llvm_is_multithreaded()) sys::MemoryFence();
+    if (llvm_is_multithreaded())
+      std::atomic_thread_fence(std::memory_order_seq_cst);
     if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>::call);
     TsanHappensAfter(this);
 

lib/IR/Attributes.cpp

@@ -18,7 +18,6 @@
 #include "LLVMContextImpl.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/IR/Type.h"
-#include "llvm/Support/Atomic.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Mutex.h"

lib/IR/DiagnosticInfo.cpp

@@ -19,14 +19,14 @@
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Metadata.h"
-#include "llvm/Support/Atomic.h"
+#include <atomic>
 #include <string>
 
 using namespace llvm;
 
 int llvm::getNextAvailablePluginDiagnosticKind() {
-  static sys::cas_flag PluginKindID = DK_FirstPluginKind;
-  return (int)sys::AtomicIncrement(&PluginKindID);
+  static std::atomic<int> PluginKindID(DK_FirstPluginKind);
+  return ++PluginKindID;
 }
 
 DiagnosticInfoInlineAsm::DiagnosticInfoInlineAsm(const Instruction &I,

lib/Support/ManagedStatic.cpp

@@ -13,7 +13,6 @@
 
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Config/config.h"
-#include "llvm/Support/Atomic.h"
 #include <cassert>
 using namespace llvm;
 
@@ -28,7 +27,7 @@ void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
       void* tmp = Creator ? Creator() : 0;
 
       TsanHappensBefore(this);
-      sys::MemoryFence();
+      std::atomic_thread_fence(std::memory_order_seq_cst);
 
       // This write is racy against the first read in the ManagedStatic
       // accessors. The race is benign because it does a second read after a

lib/Support/Statistic.cpp

@@ -76,7 +76,7 @@ void Statistic::RegisterStatistic() {
       StatInfo->addStatistic(this);
 
     TsanHappensBefore(this);
-    sys::MemoryFence();
+    std::atomic_thread_fence(std::memory_order_seq_cst);
     // Remember we have been registered.
     TsanIgnoreWritesBegin();
     Initialized = true;

lib/Support/Threading.cpp

@@ -13,8 +13,8 @@
 
 #include "llvm/Support/Threading.h"
 #include "llvm/Config/config.h"
-#include "llvm/Support/Atomic.h"
 #include "llvm/Support/Mutex.h"
+#include <atomic>
 #include <cassert>
 
 using namespace llvm;
@@ -31,7 +31,7 @@ bool llvm::llvm_start_multithreaded() {
 
   // We fence here to ensure that all initialization is complete BEFORE we
   // return from llvm_start_multithreaded().
-  sys::MemoryFence();
+  std::atomic_thread_fence(std::memory_order_seq_cst);
   return true;
 #else
   return false;
@@ -44,7 +44,7 @@ void llvm::llvm_stop_multithreaded() {
 
   // We fence here to insure that all threaded operations are complete BEFORE we
   // return from llvm_stop_multithreaded().
-  sys::MemoryFence();
+  std::atomic_thread_fence(std::memory_order_seq_cst);
 
   multithreaded_mode = false;
   delete global_lock;

lib/Support/Timer.cpp

@@ -81,14 +81,14 @@ raw_ostream *llvm::CreateInfoOutputFile() {
 static TimerGroup *DefaultTimerGroup = 0;
 static TimerGroup *getDefaultTimerGroup() {
   TimerGroup *tmp = DefaultTimerGroup;
-  sys::MemoryFence();
+  std::atomic_thread_fence(std::memory_order_seq_cst);
   if (tmp) return tmp;
   
   llvm_acquire_global_lock();
   tmp = DefaultTimerGroup;
   if (!tmp) {
     tmp = new TimerGroup("Miscellaneous Ungrouped Timers");
-    sys::MemoryFence();
+    std::atomic_thread_fence(std::memory_order_seq_cst);
     DefaultTimerGroup = tmp;
   }
   llvm_release_global_lock();