From 147ceb1991454b7a5ba6f3ec0c149dd40360a31d Mon Sep 17 00:00:00 2001
From: Sai Praveen Bangaru <31557731+saipraveenb25@users.noreply.github.com>
Date: Thu, 14 Nov 2024 12:06:17 -0500
Subject: [PATCH] Fix issue with raw default constructors in SPIRV emit (#5556)

---
 source/slang/slang-emit.cpp                   | 14 ++++++
 source/slang/slang-ir-insts.h                 |  7 +++
 .../slang-ir-strip-default-construct.cpp      | 45 +++++++++++++++++++
 .../slang/slang-ir-strip-default-construct.h  | 11 +++++
 4 files changed, 77 insertions(+)
 create mode 100644 source/slang/slang-ir-strip-default-construct.cpp
 create mode 100644 source/slang/slang-ir-strip-default-construct.h

diff --git a/source/slang/slang-emit.cpp b/source/slang/slang-emit.cpp
index 05bb12ecc7..010b4bc921 100644
--- a/source/slang/slang-emit.cpp
+++ b/source/slang/slang-emit.cpp
@@ -89,6 +89,7 @@
 #include "slang-ir-ssa.h"
 #include "slang-ir-string-hash.h"
 #include "slang-ir-strip-cached-dict.h"
+#include "slang-ir-strip-default-construct.h"
 #include "slang-ir-strip-witness-tables.h"
 #include "slang-ir-strip.h"
 #include "slang-ir-synthesize-active-mask.h"
@@ -1419,6 +1420,19 @@ Result linkAndOptimizeIR(
     // we will need to disable this pass.
     stripWitnessTables(irModule);
 
+    switch (target)
+    {
+    // On targets that don't support default initialization, remove 'raw' default construct
+    // insts because our code-gen will not have any way to emit them.
+    //
+    case CodeGenTarget::SPIRV:
+        if (targetProgram->shouldEmitSPIRVDirectly())
+            removeRawDefaultConstructors(irModule);
+        break;
+    default:
+        break;
+    }
+
 #if 0
     dumpIRIfEnabled(codeGenContext, irModule, "AFTER STRIP WITNESS TABLES");
 #endif
diff --git a/source/slang/slang-ir-insts.h b/source/slang/slang-ir-insts.h
index 4baa786e3a..9ccfce51cd 100644
--- a/source/slang/slang-ir-insts.h
+++ b/source/slang/slang-ir-insts.h
@@ -2894,6 +2894,13 @@ struct IRUndefined : IRInst
 {
 };
 
+// Special inst for targets that support default initialization,
+// like the braces '= {}' in C/HLSL
+struct IRDefaultConstruct : IRInst
+{
+    IR_LEAF_ISA(DefaultConstruct)
+};
+
 // A global-scope generic parameter (a type parameter, a
 // constraint parameter, etc.)
 struct IRGlobalGenericParam : IRInst
diff --git a/source/slang/slang-ir-strip-default-construct.cpp b/source/slang/slang-ir-strip-default-construct.cpp
new file mode 100644
index 0000000000..ea141d2fd0
--- /dev/null
+++ b/source/slang/slang-ir-strip-default-construct.cpp
@@ -0,0 +1,45 @@
+// slang-ir-strip-default-construct.cpp
+#include "slang-ir-strip-default-construct.h"
+
+#include "slang-ir-inst-pass-base.h"
+#include "slang-ir-insts.h"
+#include "slang-ir.h"
+
+namespace Slang
+{
+
+struct RemoveDefaultConstructInsts : InstPassBase
+{
+    RemoveDefaultConstructInsts(IRModule* module)
+        : InstPassBase(module)
+    {
+    }
+    void processModule()
+    {
+        processInstsOfType<IRDefaultConstruct>(
+            kIROp_DefaultConstruct,
+            [&](IRDefaultConstruct* defaultConstruct)
+            {
+                List<IRInst*> instsToRemove;
+                for (auto use = defaultConstruct->firstUse; use; use = use->nextUse)
+                {
+                    if (as<IRStore>(use->getUser()))
+                        instsToRemove.add(use->getUser());
+                    else
+                        return; // Ignore this inst if there are non-store uses.
+                }
+
+                for (auto inst : instsToRemove)
+                    inst->removeAndDeallocate();
+
+                defaultConstruct->removeAndDeallocate();
+            });
+    }
+};
+
+void removeRawDefaultConstructors(IRModule* module)
+{
+    RemoveDefaultConstructInsts(module).processModule();
+}
+
+} // namespace Slang
diff --git a/source/slang/slang-ir-strip-default-construct.h b/source/slang/slang-ir-strip-default-construct.h
new file mode 100644
index 0000000000..ea3984d8bb
--- /dev/null
+++ b/source/slang/slang-ir-strip-default-construct.h
@@ -0,0 +1,11 @@
+// slang-ir-strip-default-construct.h
+#pragma once
+
+namespace Slang
+{
+struct IRModule;
+
+/// Strip the contents of all witness table instructions from the given IR `module`
+void removeRawDefaultConstructors(IRModule* module);
+
+} // namespace Slang