Switch statistics to use relaxed updates to a std::atomic.

This removes usage of the hacky, incorrect, and TSan-unfriendly
home-grown atomics. It should actually be more efficient in some cases.

Based on our existing usage of <atomic>, all of this is portably
available AFAICT. One small challenge is initializing the stastic, but
I've tried a comparable sample out on MSVC (the most likely to complain
here) and it seems to work. Will have to watch the build bots of course.

llvm-svn: 271504
This commit is contained in:
Chandler Carruth 2016-06-02 08:44:05 +00:00
parent a30f684a67
commit 7ae684a8b4
1 changed files with 19 additions and 24 deletions

View File

@ -28,6 +28,7 @@
#include "llvm/Support/Atomic.h" #include "llvm/Support/Atomic.h"
#include "llvm/Support/Compiler.h" #include "llvm/Support/Compiler.h"
#include <atomic>
#include <memory> #include <memory>
namespace llvm { namespace llvm {
@ -38,10 +39,10 @@ class Statistic {
public: public:
const char *Name; const char *Name;
const char *Desc; const char *Desc;
volatile llvm::sys::cas_flag Value; std::atomic<unsigned> Value;
bool Initialized; bool Initialized;
llvm::sys::cas_flag getValue() const { return Value; } unsigned getValue() const { return Value.load(std::memory_order_relaxed); }
const char *getName() const { return Name; } const char *getName() const { return Name; }
const char *getDesc() const { return Desc; } const char *getDesc() const { return Desc; }
@ -52,51 +53,45 @@ public:
} }
// Allow use of this class as the value itself. // Allow use of this class as the value itself.
operator unsigned() const { return Value; } operator unsigned() const { return getValue(); }
#if !defined(NDEBUG) || defined(LLVM_ENABLE_STATS) #if !defined(NDEBUG) || defined(LLVM_ENABLE_STATS)
const Statistic &operator=(unsigned Val) { const Statistic &operator=(unsigned Val) {
Value = Val; Value.store(Val, std::memory_order_relaxed);
return init(); return init();
} }
const Statistic &operator++() { const Statistic &operator++() {
// FIXME: This function and all those that follow carefully use an Value.fetch_add(1, std::memory_order_relaxed);
// 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);
return init(); return init();
} }
unsigned operator++(int) { unsigned operator++(int) {
init(); init();
unsigned OldValue = Value; return Value.fetch_add(1, std::memory_order_relaxed);
sys::AtomicIncrement(&Value);
return OldValue;
} }
const Statistic &operator--() { const Statistic &operator--() {
sys::AtomicDecrement(&Value); Value.fetch_sub(1, std::memory_order_relaxed);
return init(); return init();
} }
unsigned operator--(int) { unsigned operator--(int) {
init(); init();
unsigned OldValue = Value; return Value.fetch_sub(1, std::memory_order_relaxed);
sys::AtomicDecrement(&Value);
return OldValue;
} }
const Statistic &operator+=(const unsigned &V) { const Statistic &operator+=(unsigned V) {
if (!V) return *this; if (V == 0)
sys::AtomicAdd(&Value, V); return *this;
Value.fetch_add(V, std::memory_order_relaxed);
return init(); return init();
} }
const Statistic &operator-=(const unsigned &V) { const Statistic &operator-=(unsigned V) {
if (!V) return *this; if (V == 0)
sys::AtomicAdd(&Value, -V); return *this;
Value.fetch_sub(V, std::memory_order_relaxed);
return init(); return init();
} }
@ -145,8 +140,8 @@ protected:
// STATISTIC - A macro to make definition of statistics really simple. This // STATISTIC - A macro to make definition of statistics really simple. This
// automatically passes the DEBUG_TYPE of the file into the statistic. // automatically passes the DEBUG_TYPE of the file into the statistic.
#define STATISTIC(VARNAME, DESC) \ #define STATISTIC(VARNAME, DESC) \
static llvm::Statistic VARNAME = { DEBUG_TYPE, DESC, 0, 0 } static llvm::Statistic VARNAME = {DEBUG_TYPE, DESC, {0}, 0}
/// \brief Enable the collection and printing of statistics. /// \brief Enable the collection and printing of statistics.
void EnableStatistics(); void EnableStatistics();