From fc452b7586ec93a52354130244fc46e13b3e4eb3 Mon Sep 17 00:00:00 2001
From: baldurk <baldurk@baldurk.org>
Date: Fri, 10 Apr 2020 12:56:10 +0100
Subject: [PATCH] Add helpers to create an empty SPIR-V module in an editor

---
 .../driver/shaders/spirv/spirv_editor.cpp     | 30 ++++++++++++++++---
 renderdoc/driver/shaders/spirv/spirv_editor.h |  1 +
 .../driver/shaders/spirv/spirv_processor.cpp  |  4 +++
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/renderdoc/driver/shaders/spirv/spirv_editor.cpp b/renderdoc/driver/shaders/spirv/spirv_editor.cpp
index ddb88a5f4..d932842a7 100644
--- a/renderdoc/driver/shaders/spirv/spirv_editor.cpp
+++ b/renderdoc/driver/shaders/spirv/spirv_editor.cpp
@@ -117,15 +117,37 @@ void Editor::Prepare()
   }
 }
 
+void Editor::CreateEmpty(uint32_t major, uint32_t minor)
+{
+  if(!m_ExternalSPIRV.empty())
+  {
+    RDCERR("Creating empty SPIR-V module with some SPIR-V words already in place!");
+    m_ExternalSPIRV.clear();
+  }
+
+  // create an empty SPIR-V header with an upper ID bound of 1
+
+  m_ExternalSPIRV = {
+      MagicNumber, (major << 16) | (minor << 8),
+      0,    // TODO maybe register a generator ID?
+      1,    // bound
+      0,    // instruction schema
+  };
+
+  // we need at least one opcode to parse properly, and we'll always need shader.
+  Operation shader = Operation(OpCapability(Capability::Shader));
+  m_ExternalSPIRV.append(&shader[0], shader.size());
+
+  Prepare();
+}
+
 Editor::~Editor()
 {
   for(size_t i = FirstRealWord; i < m_SPIRV.size();)
   {
-    while(m_SPIRV[i] == OpNopWord)
-    {
+    // don't need to update anything as we're destructing!
+    while(i < m_SPIRV.size() && m_SPIRV[i] == OpNopWord)
       m_SPIRV.erase(i);
-      addWords(i, -1);
-    }
 
     uint32_t len = m_SPIRV[i] >> WordCountShift;
 
diff --git a/renderdoc/driver/shaders/spirv/spirv_editor.h b/renderdoc/driver/shaders/spirv/spirv_editor.h
index 2aec15d0b..fa1dc4988 100644
--- a/renderdoc/driver/shaders/spirv/spirv_editor.h
+++ b/renderdoc/driver/shaders/spirv/spirv_editor.h
@@ -122,6 +122,7 @@ public:
   ~Editor();
 
   void Prepare();
+  void CreateEmpty(uint32_t major, uint32_t minor);
 
   Id MakeId();
 
diff --git a/renderdoc/driver/shaders/spirv/spirv_processor.cpp b/renderdoc/driver/shaders/spirv/spirv_processor.cpp
index 428b44c10..b9f16e001 100644
--- a/renderdoc/driver/shaders/spirv/spirv_processor.cpp
+++ b/renderdoc/driver/shaders/spirv/spirv_processor.cpp
@@ -422,6 +422,10 @@ void Processor::Parse(const rdcarray<uint32_t> &spirvWords)
   // ensure we got everything right. First section should start at the beginning
   RDCASSERTEQUAL(m_Sections[Section::First].startOffset, FirstRealWord);
 
+  // if the last section is empty, set its start ofset. This will cascade below
+  if(m_Sections[Section::Count - 1].startOffset == 0)
+    m_Sections[Section::Count - 1].startOffset = m_Sections[Section::Count - 1].endOffset;
+
   // we now set the endOffset of each section to the start of the next. Any empty sections
   // temporarily have startOffset set to endOffset, we'll pad them with a nop below.
   for(int s = Section::Count - 1; s > 0; s--)