Add memory discard message.

This can be used to erase all allocations made within the named memory
pool. The usual use case would be for arena allocators, which allocate
by advancing a pointer and never have to free the memory. There is no
tracking of individual allocations and everything is freed frequently,
by reseting the pointer, for example once per frame.

Since this is used in special-purpose allocators, there is no support
for discarding the memory of the default memory pool.

public/common/TracyQueue.hpp

@@ -42,6 +42,8 @@ enum class QueueType : uint8_t
     MemAllocCallstackNamed,
     MemFreeCallstack,
     MemFreeCallstackNamed,
+    MemDiscard,
+    MemDiscardCallstack,
     GpuZoneBegin,
     GpuZoneBeginCallstack,
     GpuZoneBeginAllocSrcLoc,
@@ -502,6 +504,13 @@ struct QueueMemFree
     uint64_t ptr;
 };
 
+struct QueueMemDiscard
+{
+    int64_t time;
+    uint32_t thread;
+    uint64_t name;
+};
+
 struct QueueCallstackFat
 {
     uint64_t ptr;
@@ -742,6 +751,7 @@ struct QueueItem
         QueueGpuContextNameFat gpuContextNameFat;
         QueueMemAlloc memAlloc;
         QueueMemFree memFree;
+        QueueMemDiscard memDiscard;
         QueueMemNamePayload memName;
         QueueThreadGroupHint threadGroupHint;
         QueueCallstackFat callstackFat;
@@ -813,6 +823,8 @@ static constexpr size_t QueueDataSize[] = {
     sizeof( QueueHeader ) + sizeof( QueueMemAlloc ),        // callstack, named
     sizeof( QueueHeader ) + sizeof( QueueMemFree ),         // callstack
     sizeof( QueueHeader ) + sizeof( QueueMemFree ),         // callstack, named
+    sizeof( QueueHeader ) + sizeof( QueueMemDiscard ),
+    sizeof( QueueHeader ) + sizeof( QueueMemDiscard ),      // callstack
     sizeof( QueueHeader ) + sizeof( QueueGpuZoneBegin ),
     sizeof( QueueHeader ) + sizeof( QueueGpuZoneBegin ),    // callstack
     sizeof( QueueHeader ) + sizeof( QueueGpuZoneBeginLean ),// allocated source location