Remove Atomic.h

The STL has everything we need nowadays.

I have tried to not alter any behavior or semantics with this
change wherever possible. In particular, WriteLow and WriteHigh
in CommandProcessor retain the ability to accidentally undo
another thread's write to the upper half or lower half
respectively. If that should be fixed, it should be done in a
separate commit for clarity. One thing did change: The places
where we were using += on a volatile variable (not an atomic
operation) are now using fetch_add (actually an atomic operation).

Tested with single core and dual core on x86-64 and AArch64.

Source/Core/VideoCommon/Fifo.cpp

@@ -8,7 +8,6 @@
 #include <cstring>
 
 #include "Common/Assert.h"
-#include "Common/Atomic.h"
 #include "Common/BlockingLoop.h"
 #include "Common/ChunkFile.h"
 #include "Common/Event.h"
@@ -329,33 +328,37 @@ void RunGpuLoop()
 
           // check if we are able to run this buffer
           while (!CommandProcessor::IsInterruptWaiting() && fifo.bFF_GPReadEnable &&
-                 fifo.CPReadWriteDistance && !AtBreakpoint())
+                 fifo.CPReadWriteDistance.load(std::memory_order_relaxed) && !AtBreakpoint())
           {
             if (param.bSyncGPU && s_sync_ticks.load() < param.iSyncGpuMinDistance)
               break;
 
             u32 cyclesExecuted = 0;
-            u32 readPtr = fifo.CPReadPointer;
+            u32 readPtr = fifo.CPReadPointer.load(std::memory_order_relaxed);
             ReadDataFromFifo(readPtr);
 
-            if (readPtr == fifo.CPEnd)
-              readPtr = fifo.CPBase;
+            if (readPtr == fifo.CPEnd.load(std::memory_order_relaxed))
+              readPtr = fifo.CPBase.load(std::memory_order_relaxed);
             else
               readPtr += 32;
 
-            ASSERT_MSG(COMMANDPROCESSOR, (s32)fifo.CPReadWriteDistance - 32 >= 0,
+            ASSERT_MSG(COMMANDPROCESSOR,
+                       (s32)fifo.CPReadWriteDistance.load(std::memory_order_relaxed) - 32 >= 0,
                        "Negative fifo.CPReadWriteDistance = %i in FIFO Loop !\nThat can produce "
                        "instability in the game. Please report it.",
-                       fifo.CPReadWriteDistance - 32);
+                       fifo.CPReadWriteDistance.load(std::memory_order_relaxed) - 32);
 
             u8* write_ptr = s_video_buffer_write_ptr;
             s_video_buffer_read_ptr = OpcodeDecoder::Run(
                 DataReader(s_video_buffer_read_ptr, write_ptr), &cyclesExecuted, false);
 
-            Common::AtomicStore(fifo.CPReadPointer, readPtr);
-            Common::AtomicAdd(fifo.CPReadWriteDistance, static_cast<u32>(-32));
+            fifo.CPReadPointer.store(readPtr, std::memory_order_relaxed);
+            fifo.CPReadWriteDistance.fetch_sub(32, std::memory_order_seq_cst);
             if ((write_ptr - s_video_buffer_read_ptr) == 0)
-              Common::AtomicStore(fifo.SafeCPReadPointer, fifo.CPReadPointer);
+            {
+              fifo.SafeCPReadPointer.store(fifo.CPReadPointer.load(std::memory_order_relaxed),
+                                           std::memory_order_relaxed);
+            }
 
             CommandProcessor::SetCPStatusFromGPU();
 
@@ -412,7 +415,8 @@ void GpuMaySleep()
 bool AtBreakpoint()
 {
   CommandProcessor::SCPFifoStruct& fifo = CommandProcessor::fifo;
-  return fifo.bFF_BPEnable && (fifo.CPReadPointer == fifo.CPBreakpoint);
+  return fifo.bFF_BPEnable && (fifo.CPReadPointer.load(std::memory_order_relaxed) ==
+                               fifo.CPBreakpoint.load(std::memory_order_relaxed));
 }
 
 void RunGpu()
@@ -442,12 +446,12 @@ static int RunGpuOnCpu(int ticks)
   CommandProcessor::SCPFifoStruct& fifo = CommandProcessor::fifo;
   bool reset_simd_state = false;
   int available_ticks = int(ticks * SConfig::GetInstance().fSyncGpuOverclock) + s_sync_ticks.load();
-  while (fifo.bFF_GPReadEnable && fifo.CPReadWriteDistance && !AtBreakpoint() &&
-         available_ticks >= 0)
+  while (fifo.bFF_GPReadEnable && fifo.CPReadWriteDistance.load(std::memory_order_relaxed) &&
+         !AtBreakpoint() && available_ticks >= 0)
   {
     if (s_use_deterministic_gpu_thread)
     {
-      ReadDataFromFifoOnCPU(fifo.CPReadPointer);
+      ReadDataFromFifoOnCPU(fifo.CPReadPointer.load(std::memory_order_relaxed));
       s_gpu_mainloop.Wakeup();
     }
     else
@@ -458,19 +462,25 @@ static int RunGpuOnCpu(int ticks)
         FPURoundMode::LoadDefaultSIMDState();
         reset_simd_state = true;
       }
-      ReadDataFromFifo(fifo.CPReadPointer);
+      ReadDataFromFifo(fifo.CPReadPointer.load(std::memory_order_relaxed));
       u32 cycles = 0;
       s_video_buffer_read_ptr = OpcodeDecoder::Run(
           DataReader(s_video_buffer_read_ptr, s_video_buffer_write_ptr), &cycles, false);
       available_ticks -= cycles;
     }
 
-    if (fifo.CPReadPointer == fifo.CPEnd)
-      fifo.CPReadPointer = fifo.CPBase;
+    if (fifo.CPReadPointer.load(std::memory_order_relaxed) ==
+        fifo.CPEnd.load(std::memory_order_relaxed))
+    {
+      fifo.CPReadPointer.store(fifo.CPBase.load(std::memory_order_relaxed),
+                               std::memory_order_relaxed);
+    }
     else
-      fifo.CPReadPointer += 32;
+    {
+      fifo.CPReadPointer.fetch_add(32, std::memory_order_relaxed);
+    }
 
-    fifo.CPReadWriteDistance -= 32;
+    fifo.CPReadWriteDistance.fetch_sub(32, std::memory_order_relaxed);
   }
 
   CommandProcessor::SetCPStatusFromGPU();