[GPU/D3D12] Memexport from anywhere in control flow + 8/16bpp memexport

There's no limit on the number of memory exports in a shader on the real
Xenos, and exports can be done anywhere, including in loops. Now, instead
of deferring the exports to the end of the shader, and assuming that export
allocs are executed only once, Xenia flushes exports when it reaches an
alloc (allocs terminate memory exports on Xenos, as well as individual ALU
instructions with `serialize`, but not handling this case for simplicity,
it's only truly mandatory to flush memory exports before starting a new
one), the end of the shader, or a pixel with outstanding exports is killed.

To know which eM# registers need to be flushed to the memory, traversing
the successors of each exec potentially writing any eM#, and specifying
that certain eM# registers might have potentially been written before each
reached control flow instruction, until a flush point or the end of the
shader is reached.

Also, some games export to sub-32bpp formats. These are now supported via
atomic AND clearing the bits of the dword to replace followed by an atomic
OR inserting the new byte/short.

src/xenia/gpu/d3d12/d3d12_command_processor.h

@@ -18,6 +18,7 @@
 #include <string>
 #include <unordered_map>
 #include <utility>
+#include <vector>
 
 #include "xenia/base/assert.h"
 #include "xenia/gpu/command_processor.h"
@@ -378,13 +379,6 @@ class D3D12CommandProcessor : public CommandProcessor {
                       ID3D12RootSignature* root_signature,
                       bool shared_memory_is_uav);
 
-  // Returns dword count for one element for a memexport format, or 0 if it's
-  // not supported by the D3D12 command processor (if it's smaller that 1 dword,
-  // for instance).
-  // TODO(Triang3l): Check if any game uses memexport with formats smaller than
-  // 32 bits per element.
-  static uint32_t GetSupportedMemExportFormatSize(xenos::ColorFormat format);
-
   // Returns a buffer for reading GPU data back to the CPU. Assuming
   // synchronizing immediately after use. Always in COPY_DEST state.
   ID3D12Resource* RequestReadbackBuffer(uint32_t size);
@@ -684,6 +678,9 @@ class D3D12CommandProcessor : public CommandProcessor {
 
   // Current primitive topology.
   D3D_PRIMITIVE_TOPOLOGY primitive_topology_;
+
+  // Temporary storage for memexport stream constants used in the draw.
+  std::vector<draw_util::MemExportRange> memexport_ranges_;
 };
 
 }  // namespace d3d12