Fetch dispatch thread dimension always even if we don't disassemble

* We need the dispatch thread dimension to be valid when creating the
  shader reflection data, which may happen before we've disassembled the
  bytecode.
* We do a minimal pass just to skip to that opcode and extract the dims.

renderdoc/driver/shaders/dxbc/dxbc_disassemble.cpp

@@ -294,6 +294,47 @@ void DXBCFile::FetchTypeVersion()
   m_Version.Minor = VersionToken::MinorVersion.Get(cur[0]);
 }
 
+void DXBCFile::FetchThreadDim()
+{
+  if(m_HexDump.empty())
+    return;
+
+  uint32_t *begin = &m_HexDump.front();
+  uint32_t *cur = begin;
+  uint32_t *end = &m_HexDump.back();
+
+  // skip header dword above
+  cur++;
+
+  // skip length dword
+  cur++;
+
+  while(cur < end)
+  {
+    uint32_t OpcodeToken0 = cur[0];
+
+    OpcodeType op = Opcode::Type.Get(OpcodeToken0);
+
+    if(op == OPCODE_DCL_THREAD_GROUP)
+    {
+      DispatchThreadsDimension[0] = cur[1];
+      DispatchThreadsDimension[1] = cur[2];
+      DispatchThreadsDimension[2] = cur[3];
+      break;
+    }
+
+    if(op == OPCODE_CUSTOMDATA)
+    {
+      // length in opcode token is 0, full length is in second dword
+      cur += cur[1];
+    }
+    else
+    {
+      cur += Opcode::Length.Get(OpcodeToken0);
+    }
+  }
+}
+
 void DXBCFile::DisassembleHexDump()
 {
   if(m_Disassembled)

renderdoc/driver/shaders/dxbc/dxbc_inspect.cpp

@@ -847,6 +847,12 @@ DXBCFile::DXBCFile(const void *ByteCode, size_t ByteCodeLength)
     m_GuessedResources = true;
   }
 
+  // make sure to fetch the dispatch threads dimension from disassembly
+  if(!m_Disassembled && m_Type == D3D11_ShaderType_Compute)
+  {
+    FetchThreadDim();
+  }
+
   for(uint32_t chunkIdx = 0; chunkIdx < header->numChunks; chunkIdx++)
   {
     uint32_t *fourcc = (uint32_t *)(data + chunkOffsets[chunkIdx]);

renderdoc/driver/shaders/dxbc/dxbc_inspect.h

@@ -405,6 +405,7 @@ private:
   DXBCFile(const DXBCFile &o);
   DXBCFile &operator=(const DXBCFile &o);
 
+  void FetchThreadDim();
   void FetchTypeVersion();
   void DisassembleHexDump();
   void MakeDisassemblyString();