Add method for inserting deferred constants in SPIR-V

* Our iterators currently don't update when insertions are made before them, so
  adding constants while modifying a function is a problem. However we can just
  reserve an ID and add the constant later.

renderdoc/driver/shaders/spirv/spirv_editor.cpp

@@ -143,6 +143,10 @@ void Editor::CreateEmpty(uint32_t major, uint32_t minor)
 
 Editor::~Editor()
 {
+  for(const Operation &op : m_DeferredConstants)
+    AddConstant(op);
+  m_DeferredConstants.clear();
+
   m_ExternalSPIRV.clear();
   m_ExternalSPIRV.reserve(m_SPIRV.size());
 

renderdoc/driver/shaders/spirv/spirv_editor.h

@@ -210,6 +210,22 @@ public:
     return ret;
   }
 
+  template <typename T>
+  Id AddConstantDeferred(T t)
+  {
+    Id typeId = DeclareType(scalar<T>());
+    Id retId = MakeId();
+    rdcarray<uint32_t> words = {typeId.value(), retId.value()};
+
+    words.resize(words.size() + (sizeof(T) + 3) / 4);
+
+    memcpy(&words[2], &t, sizeof(T));
+
+    m_DeferredConstants.add(Operation(Op::Constant, words));
+
+    return retId;
+  }
+
 private:
   using Processor::Parse;
   inline void addWords(size_t offs, size_t num) { addWords(offs, (int32_t)num); }
@@ -246,6 +262,8 @@ private:
   template <typename SPIRVType>
   const std::map<SPIRVType, Id> &GetTable() const;
 
+  OperationList m_DeferredConstants;
+
   rdcarray<uint32_t> &m_ExternalSPIRV;
 };