Various dxc/fxc compatibility fixes. (#2863)

* Various dxc/fxc compatibility fixes.

* Cleanup.

* Fix test cases.

* Fix comments.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

1 files changed, 47 insertions, 2 deletions

diff --git a/source/slang/slang-emit-hlsl.cpp b/source/slang/slang-emit-hlsl.cpp
index e07d9facc..434f0803e 100644
--- a/source/slang/slang-emit-hlsl.cpp
+++ b/source/slang/slang-emit-hlsl.cpp
@@ -208,10 +208,20 @@ void HLSLSourceEmitter::_emitHLSLParameterGroup(IRGlobalParam* varDecl, IRUnifor
 
     _emitHLSLRegisterSemantic(LayoutResourceKind::ConstantBuffer, &containerChain);
 
+    auto elementType = type->getElementType();
+    if (hasExplicitConstantBufferOffset(type))
+    {
+        // If the user has provided any explicit `packoffset` modifiers,
+        // we have to unwrap the struct and emit the fields directly.
+        emitStructDeclarationsBlock(as<IRStructType>(elementType), true);
+        m_writer->emit("\n");
+        return;
+    }
+    
+    
     m_writer->emit("\n{\n");
     m_writer->indent();
 
-    auto elementType = type->getElementType();
 
     emitType(elementType, getName(varDecl));
     m_writer->emit(";\n");
@@ -989,7 +999,7 @@ void HLSLSourceEmitter::emitRateQualifiersImpl(IRRate* rate)
     }
 }
 
-void HLSLSourceEmitter::emitSemanticsImpl(IRInst* inst)
+void HLSLSourceEmitter::emitSemanticsImpl(IRInst* inst, bool allowOffsets)
 {
     if (auto semanticDecoration = inst->findDecoration<IRSemanticDecoration>())
     {
@@ -997,6 +1007,33 @@ void HLSLSourceEmitter::emitSemanticsImpl(IRInst* inst)
         m_writer->emit(semanticDecoration->getSemanticName());
         return;
     }
+    else if (auto packOffsetDecoration = inst->findDecoration<IRPackOffsetDecoration>())
+    {
+        if (allowOffsets)
+        {
+            m_writer->emit(" : packoffset(c");
+            m_writer->emit(packOffsetDecoration->getRegisterOffset()->getValue());
+            if (packOffsetDecoration->getComponentOffset())
+            {
+                switch (packOffsetDecoration->getComponentOffset()->getValue())
+                {
+                case 0:
+                    break;
+                case 1:
+                    m_writer->emit(".y");
+                    break;
+                case 2:
+                    m_writer->emit(".z");
+                    break;
+                case 3:
+                    m_writer->emit(".w");
+                    break;
+                }
+            }
+            m_writer->emit(")");
+            return;
+        }
+    }
 
     if( auto readAccessSemantic = inst->findDecoration<IRStageReadAccessDecoration>())
         _emitStageAccessSemantic(readAccessSemantic, "read");
@@ -1114,6 +1151,14 @@ void HLSLSourceEmitter::emitInterpolationModifiersImpl(IRInst* varInst, IRType*
     }
 }
 
+void HLSLSourceEmitter::emitPackOffsetModifier(IRInst* varInst, IRType* valueType, IRPackOffsetDecoration* layout)
+{
+    SLANG_UNUSED(varInst);
+    SLANG_UNUSED(valueType);
+    SLANG_UNUSED(layout);
+    // We emit packoffset as a semantic in `emitSemantic`, so nothing to do here.
+}
+
 void HLSLSourceEmitter::emitMeshOutputModifiersImpl(IRInst* varInst)
 {
     if(auto modifier = varInst->findDecoration<IRMeshOutputDecoration>())