Fix issue with raw default constructors in SPIRV emit (shader-slang#5556)

Author: saipraveenb25

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

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

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

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