[dxvk] Remove interpolation decorations for replaced shader inputs

src/dxvk/dxvk_shader.cpp

@@ -318,16 +318,37 @@ namespace dxvk {
       }
     }
 
-    // Remove location declarations
-    for (auto ins : code) {
-      if (ins.opCode() == spv::OpDecorate
-       && ins.arg(2) == spv::DecorationLocation
-       && ins.arg(1) == inputVarId) {
-        code.beginInsertion(ins.offset());
-        code.erase(4);
-        code.endInsertion();
-        break;
+    // Remove location and other declarations
+    for (auto iter = code.begin(); iter != code.end(); ) {
+      auto ins = *(iter++);
+
+      if (ins.opCode() == spv::OpDecorate && ins.arg(1) == inputVarId) {
+        uint32_t numWords;
+
+        switch (ins.arg(2)) {
+          case spv::DecorationLocation:
+          case spv::DecorationFlat:
+          case spv::DecorationNoPerspective:
+          case spv::DecorationCentroid:
+          case spv::DecorationPatch:
+          case spv::DecorationSample:
+            numWords = ins.length();
+            break;
+
+          default:
+            numWords = 0;
+        }
+
+        if (numWords) {
+          code.beginInsertion(ins.offset());
+          code.erase(numWords);
+
+          iter = SpirvInstructionIterator(code.data(), code.endInsertion(), code.dwords());
+        }
       }
+
+      if (ins.opCode() == spv::OpFunction)
+        break;
     }
 
     // Fix up pointer types used in access chain instructions

src/spirv/spirv_code_buffer.h

@@ -208,9 +208,10 @@ namespace dxvk {
      * After this call, new instructions will be
      * appended to the stream. In other words,
      * this will restore default behaviour.
+     * \returns Previous instruction pointer
      */
-    void endInsertion() {
-      m_ptr = m_code.size();
+    size_t endInsertion() {
+      return std::exchange(m_ptr, m_code.size());
     }
     
   private:

src/spirv/spirv_instruction.h

@@ -109,7 +109,7 @@ namespace dxvk {
     : m_code  (length != 0 ? code   : nullptr),
       m_offset(length != 0 ? offset : 0),
       m_length(length) {
-      if ((length >= 5) && (m_code[0] == spv::MagicNumber))
+      if ((length >= 5) && (offset == 0) && (m_code[0] == spv::MagicNumber))
         this->advance(5);
     }
     
@@ -118,6 +118,12 @@ namespace dxvk {
       return *this;
     }
     
+    SpirvInstructionIterator operator ++ (int) {
+      SpirvInstructionIterator result = *this;
+      this->advance(SpirvInstruction(m_code, m_offset, m_length).length());
+      return result;
+    }
+    
     SpirvInstruction operator * () const {
       return SpirvInstruction(m_code, m_offset, m_length);
     }