Remove all of the legacy home-grown atomic operations LLVM provided except for CompareAndSwap. That is the only one still being used anywhere now that statistics have been moved onto std::atomic.

[chandlerc]

Summary

Also, add a warning to the header that we shouldn't introduce more uses
of these old style atomics and instead should be using C++11's
std::atomic facilities.

Really hoping that we can hammer out the last couple of users here and
replace them with something more localized and/or principled, but
figured this was a pretty good start. =]

Note that this patch will need to be reverted if r271504 needs to be
reverted as that removes the last user of these. However, the biggest
risk for that patch was MSVC 2013 and at least one bot has already
passed where it would have failed there. I've tested MSVC 2015 using
their web interfaces and other platforms seem fine, so I'm optimistic.

[rnk]

lgtm, looks like r271504 stuck since last night.

[emaste]

As an aside it looks like there's some missing dependency data in the build; on FreeBSD my Clang build failed with lots of ../lib/CodeGen/TwoAddressInstructionPass.cpp:(.text+0x39ed): undefined reference to 'llvm::sys::AtomicIncrement(unsigned int volatile*)' but worked once I deleted TwoAddressInstructionPass.cpp.o and rebuilt.

[chandlerc]

No idea...

include/llvm/Support/Atomic.h

 //===- llvm/Support/Atomic.h - Atomic Operations -----------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares the llvm::sys atomic operations.
 //
+// DO NOT USE IN NEW CODE!
+//
+// New code should always rely on the std::atomic facilities in C++11.
+//
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_ATOMIC_H
 #define LLVM_SUPPORT_ATOMIC_H
 
 #include "llvm/Support/DataTypes.h"
 
 namespace llvm {
   namespace sys {
     void MemoryFence();
 
 #ifdef _MSC_VER
     typedef long cas_flag;
 #else
     typedef uint32_t cas_flag;
 #endif
     cas_flag CompareAndSwap(volatile cas_flag* ptr,
                             cas_flag new_value,
                             cas_flag old_value);
-    cas_flag AtomicIncrement(volatile cas_flag* ptr);
-    cas_flag AtomicDecrement(volatile cas_flag* ptr);
-    cas_flag AtomicAdd(volatile cas_flag* ptr, cas_flag val);
-    cas_flag AtomicMul(volatile cas_flag* ptr, cas_flag val);
-    cas_flag AtomicDiv(volatile cas_flag* ptr, cas_flag val);
   }
 }
 
 #endif

lib/Support/Atomic.cpp

 #elif defined(GNU_ATOMICS)
   return __sync_val_compare_and_swap(ptr, old_value, new_value);
 #elif defined(_MSC_VER)
   return InterlockedCompareExchange(ptr, new_value, old_value);
 #else
 #  error No compare-and-swap implementation for your platform!
 #endif
 }
-
-sys::cas_flag sys::AtomicIncrement(volatile sys::cas_flag* ptr) {
-#if LLVM_HAS_ATOMICS == 0
-  ++(*ptr);
-  return *ptr;
-#elif defined(GNU_ATOMICS)
-  return __sync_add_and_fetch(ptr, 1);
-#elif defined(_MSC_VER)
-  return InterlockedIncrement(ptr);
-#else
-#  error No atomic increment implementation for your platform!
-#endif
-}
-
-sys::cas_flag sys::AtomicDecrement(volatile sys::cas_flag* ptr) {
-#if LLVM_HAS_ATOMICS == 0
-  --(*ptr);
-  return *ptr;
-#elif defined(GNU_ATOMICS)
-  return __sync_sub_and_fetch(ptr, 1);
-#elif defined(_MSC_VER)
-  return InterlockedDecrement(ptr);
-#else
-#  error No atomic decrement implementation for your platform!
-#endif
-}
-
-sys::cas_flag sys::AtomicAdd(volatile sys::cas_flag* ptr, sys::cas_flag val) {
-#if LLVM_HAS_ATOMICS == 0
-  *ptr += val;
-  return *ptr;
-#elif defined(GNU_ATOMICS)
-  return __sync_add_and_fetch(ptr, val);
-#elif defined(_MSC_VER)
-  return InterlockedExchangeAdd(ptr, val) + val;
-#else
-#  error No atomic add implementation for your platform!
-#endif
-}
-
-sys::cas_flag sys::AtomicMul(volatile sys::cas_flag* ptr, sys::cas_flag val) {
-  sys::cas_flag original, result;
-  do {
-    original = *ptr;
-    result = original * val;
-  } while (sys::CompareAndSwap(ptr, result, original) != original);
-
-  return result;
-}
-
-sys::cas_flag sys::AtomicDiv(volatile sys::cas_flag* ptr, sys::cas_flag val) {
-  sys::cas_flag original, result;
-  do {
-    original = *ptr;
-    result = original / val;
-  } while (sys::CompareAndSwap(ptr, result, original) != original);
-
-  return result;
-}