Refactor prelude emit (#2236)

* #include an absolute path didn't work - because paths were taken to always be relative.

* Refactor how prelude output works in emit.

* Small improvement to emit output.

* Move around comment on target specific language directives based on review.

Co-authored-by: Theresa Foley <10618364+tangent-vector@users.noreply.github.com>

11 files changed, 157 insertions, 153 deletions

diff --git a/source/slang/slang-emit-c-like.cpp b/source/slang/slang-emit-c-like.cpp
index a6edc0a1f..895421783 100644
--- a/source/slang/slang-emit-c-like.cpp
+++ b/source/slang/slang-emit-c-like.cpp
@@ -106,6 +106,11 @@ SlangResult CLikeSourceEmitter::init()
     return SLANG_OK;
 }
 
+void CLikeSourceEmitter::emitFrontMatterImpl(TargetRequest* targetReq)
+{
+    SLANG_UNUSED(targetReq);
+}
+
 //
 // Types
 //
@@ -534,26 +539,6 @@ UInt CLikeSourceEmitter::getBindingSpace(EmitVarChain* chain, LayoutResourceKind
     return space;
 }
 
-void CLikeSourceEmitter::emitLayoutDirectives(TargetRequest* targetReq)
-{
-    // We are going to emit the target-language-specific directives
-    // needed to get the default matrix layout to match what was requested
-    // for the given target.
-    //
-    // Note: we do not rely on the defaults for the target language,
-    // because a user could take the HLSL/GLSL generated by Slang and pass
-    // it to another compiler with non-default options specified on
-    // the command line, leading to all kinds of trouble.
-    //
-    // TODO: We need an approach to "global" layout directives that will work
-    // in the presence of multiple modules. If modules A and B were each
-    // compiled with different assumptions about how layout is performed,
-    // then types/variables defined in those modules should be emitted in
-    // a way that is consistent with that layout...
-
-    emitLayoutDirectivesImpl(targetReq);
-}
-
 UInt CLikeSourceEmitter::allocateUniqueID()
 {
     return m_uniqueIDCounter++;
diff --git a/source/slang/slang-emit-c-like.h b/source/slang/slang-emit-c-like.h
index 51e54611e..ddda94e84 100644
--- a/source/slang/slang-emit-c-like.h
+++ b/source/slang/slang-emit-c-like.h
@@ -261,9 +261,6 @@ public:
     UInt getBindingOffset(EmitVarChain* chain, LayoutResourceKind kind);
     UInt getBindingSpace(EmitVarChain* chain, LayoutResourceKind kind);
 
-        /// Emit directives to control overall layout computation for the emitted code.
-    void emitLayoutDirectives(TargetRequest* targetReq);
-
         // Utility code for generating unique IDs as needed
         // during the emit process (e.g., for declarations
         // that didn't originally have names, but now need to).
@@ -398,17 +395,15 @@ public:
 
     void executeEmitActions(List<EmitAction> const& actions);
 
+        // Emits front matter, that occurs before the prelude
+        // Doesn't emit generated function/types that's handled by emitPreModule
+    void emitFrontMatter(TargetRequest* targetReq) { emitFrontMatterImpl(targetReq); }
+
+    void emitPreModule() { emitPreModuleImpl(); }
+
     void emitModule(IRModule* module, DiagnosticSink* sink)
         { m_irModule = module; emitModuleImpl(module, sink); }
 
-        /// Emit any preprocessor directives that should come *before* the prelude code
-        ///
-        /// These are directives that are intended to customize some aspect(s) of the
-        /// prelude's behavior.
-        ///
-    void emitPreludeDirectives() { emitPreludeDirectivesImpl(); }
-
-    void emitPreprocessorDirectives() { emitPreprocessorDirectivesImpl(); }
     void emitSimpleType(IRType* type);
 
     void emitVectorTypeName(IRType* elementType, IRIntegerValue elementCount) { emitVectorTypeNameImpl(elementType, elementCount); }
@@ -438,9 +433,14 @@ public:
 
     virtual void emitImageFormatModifierImpl(IRInst* varDecl, IRType* varType) { SLANG_UNUSED(varDecl); SLANG_UNUSED(varType); }
     virtual void emitLayoutQualifiersImpl(IRVarLayout* layout) { SLANG_UNUSED(layout); }
-    virtual void emitPreludeDirectivesImpl() {}
-    virtual void emitPreprocessorDirectivesImpl() {}
-    virtual void emitLayoutDirectivesImpl(TargetRequest* targetReq) { SLANG_UNUSED(targetReq); }
+
+        /// Emit front matter inserting prelude where appropriate
+    virtual void emitFrontMatterImpl(TargetRequest* targetReq);
+        /// Emit any declarations, and other material that is needed before the modules contents
+        /// For example on targets that don't have built in vector/matrix support, this is where
+        /// the appropriate generated declarations occur.
+    virtual void emitPreModuleImpl() {}
+
     virtual void emitRateQualifiersImpl(IRRate* rate) { SLANG_UNUSED(rate); }
     virtual void emitSemanticsImpl(IRInst* inst) { SLANG_UNUSED(inst);  }
     virtual void emitSimpleFuncParamImpl(IRParam* param);
diff --git a/source/slang/slang-emit-cpp.cpp b/source/slang/slang-emit-cpp.cpp
index 81d32c297..9887f1ba6 100644
--- a/source/slang/slang-emit-cpp.cpp
+++ b/source/slang/slang-emit-cpp.cpp
@@ -2459,15 +2459,13 @@ static Index _calcTypeOrder(IRType* a)
     }
 }
 
-void CPPSourceEmitter::emitPreprocessorDirectivesImpl()
+void CPPSourceEmitter::emitPreModuleImpl()
 {
-    SourceWriter* writer = getSourceWriter();
-
-    writer->emit("\n");
-
-    
     if (m_target == CodeGenTarget::CPPSource)
     {
+        // NOTE, that this opens an anonymous scope. 
+        // The scope is closed in `emitModuleImpl`
+
         // When generating kernel code in C++, put all into an anonymous namespace
         // This includes any generated types, and generated intrinsics.
         m_writer->emit("namespace { // anonymous \n\n");
@@ -2476,6 +2474,8 @@ void CPPSourceEmitter::emitPreprocessorDirectivesImpl()
         m_writer->emit("#endif\n\n");
     }
 
+    // Emit generated functions and types
+
     if (m_target == CodeGenTarget::CSource)
     {
         // For C output we need to emit type definitions.
@@ -2507,7 +2507,7 @@ void CPPSourceEmitter::emitPreprocessorDirectivesImpl()
         m_intrinsicSet.getIntrinsics(intrinsics);
 
         // Emit all the intrinsics that were used
-        for (auto intrinsic: intrinsics)
+        for (auto intrinsic : intrinsics)
         {
             _maybeEmitSpecializedOperationDefinition(intrinsic);
         }
@@ -2757,7 +2757,6 @@ void CPPSourceEmitter::emitModuleImpl(IRModule* module, DiagnosticSink* sink)
     
     _emitForwardDeclarations(actions);
 
-    
     {
         // Output all the thread locals 
         for (auto action : actions)
diff --git a/source/slang/slang-emit-cpp.h b/source/slang/slang-emit-cpp.h
index dc9f78df2..0d9327b9e 100644
--- a/source/slang/slang-emit-cpp.h
+++ b/source/slang/slang-emit-cpp.h
@@ -59,7 +59,7 @@ protected:
     virtual void _emitType(IRType* type, DeclaratorInfo* declarator) SLANG_OVERRIDE;
     virtual void emitVectorTypeNameImpl(IRType* elementType, IRIntegerValue elementCount) SLANG_OVERRIDE;
     virtual bool tryEmitInstExprImpl(IRInst* inst, const EmitOpInfo& inOuterPrec) SLANG_OVERRIDE;
-    virtual void emitPreprocessorDirectivesImpl() SLANG_OVERRIDE;
+    virtual void emitPreModuleImpl() SLANG_OVERRIDE;
     virtual void emitSimpleValueImpl(IRInst* value) SLANG_OVERRIDE;
     virtual void emitSimpleFuncParamImpl(IRParam* param) SLANG_OVERRIDE;
     virtual void emitModuleImpl(IRModule* module, DiagnosticSink* sink) SLANG_OVERRIDE;
diff --git a/source/slang/slang-emit-cuda.cpp b/source/slang/slang-emit-cuda.cpp
index f7850179d..eda30b956 100644
--- a/source/slang/slang-emit-cuda.cpp
+++ b/source/slang/slang-emit-cuda.cpp
@@ -840,11 +840,6 @@ void CUDASourceEmitter::handleRequiredCapabilitiesImpl(IRInst* inst)
     }
 }
 
-void CUDASourceEmitter::emitLayoutDirectivesImpl(TargetRequest* targetReq)
-{
-    SLANG_UNUSED(targetReq);
-}
-
 void CUDASourceEmitter::emitVectorTypeNameImpl(IRType* elementType, IRIntegerValue elementCount)
 {
     m_writer->emit(getVectorPrefix(elementType->getOp()));
@@ -933,10 +928,12 @@ void CUDASourceEmitter::emitMatrixLayoutModifiersImpl(IRVarLayout* layout)
     Super::emitMatrixLayoutModifiersImpl(layout);
 }
 
-void CUDASourceEmitter::emitPreprocessorDirectivesImpl()
+void CUDASourceEmitter::emitPreModuleImpl()
 {
     SourceWriter* writer = getSourceWriter();
 
+    // Emit generated types/functions
+
     writer->emit("\n");
 
     {
@@ -961,6 +958,7 @@ void CUDASourceEmitter::emitPreprocessorDirectivesImpl()
     }
 }
 
+
 bool CUDASourceEmitter::tryEmitGlobalParamImpl(IRGlobalParam* varDecl, IRType* varType)
 {
     // A global shader parameter in the IR for CUDA output will
diff --git a/source/slang/slang-emit-cuda.h b/source/slang/slang-emit-cuda.h
index 8bd2d33c4..ff947fe58 100644
--- a/source/slang/slang-emit-cuda.h
+++ b/source/slang/slang-emit-cuda.h
@@ -65,7 +65,9 @@ protected:
     virtual void emitLayoutSemanticsImpl(IRInst* inst, char const* uniformSemanticSpelling) SLANG_OVERRIDE;
     virtual void emitParameterGroupImpl(IRGlobalParam* varDecl, IRUniformParameterGroupType* type) SLANG_OVERRIDE;
     virtual void emitEntryPointAttributesImpl(IRFunc* irFunc, IREntryPointDecoration* entryPointDecor) SLANG_OVERRIDE;
-    virtual void emitLayoutDirectivesImpl(TargetRequest* targetReq) SLANG_OVERRIDE;
+    
+    virtual void emitPreModuleImpl() SLANG_OVERRIDE;
+
     virtual void emitRateQualifiersImpl(IRRate* rate) SLANG_OVERRIDE;
     virtual void emitSemanticsImpl(IRInst* inst) SLANG_OVERRIDE;
     virtual void emitSimpleFuncImpl(IRFunc* func) SLANG_OVERRIDE;
@@ -91,8 +93,7 @@ protected:
     virtual bool tryEmitGlobalParamImpl(IRGlobalParam* varDecl, IRType* varType) SLANG_OVERRIDE;
     virtual bool tryEmitInstExprImpl(IRInst* inst, const EmitOpInfo& inOuterPrec) SLANG_OVERRIDE;
 
-    virtual void emitPreprocessorDirectivesImpl() SLANG_OVERRIDE;
-
+    
     virtual void emitModuleImpl(IRModule* module, DiagnosticSink* sink) SLANG_OVERRIDE;
 
     // CPPSourceEmitter overrides 
diff --git a/source/slang/slang-emit-glsl.cpp b/source/slang/slang-emit-glsl.cpp
index 7578a2dd5..d9c81f14b 100644
--- a/source/slang/slang-emit-glsl.cpp
+++ b/source/slang/slang-emit-glsl.cpp
@@ -12,6 +12,10 @@
 
 namespace Slang {
 
+void trackGLSLTargetCaps(
+    GLSLExtensionTracker* extensionTracker,
+    CapabilitySet const& caps);
+
 GLSLSourceEmitter::GLSLSourceEmitter(const Desc& desc) :
     Super(desc)
 {
@@ -1740,7 +1744,33 @@ void GLSLSourceEmitter::handleRequiredCapabilitiesImpl(IRInst* inst)
     }
 }
 
-void GLSLSourceEmitter::emitPreprocessorDirectivesImpl()
+static Index _getGLSLVersion(ProfileVersion profile)
+{
+    switch (profile)
+    {
+#define CASE(TAG, VALUE) case ProfileVersion::TAG: return VALUE; 
+        CASE(GLSL_110, 110);
+        CASE(GLSL_120, 120);
+        CASE(GLSL_130, 130);
+        CASE(GLSL_140, 140);
+        CASE(GLSL_150, 150);
+        CASE(GLSL_330, 330);
+        CASE(GLSL_400, 400);
+        CASE(GLSL_410, 410);
+        CASE(GLSL_420, 420);
+        CASE(GLSL_430, 430);
+        CASE(GLSL_440, 440);
+        CASE(GLSL_450, 450);
+        CASE(GLSL_460, 460);
+#undef CASE
+
+    default:
+        break;
+    }
+    return -1;
+}
+
+void GLSLSourceEmitter::emitFrontMatterImpl(TargetRequest* targetReq)
 {
     auto effectiveProfile = m_effectiveProfile;
     if (effectiveProfile.getFamily() == ProfileFamily::GLSL)
@@ -1759,44 +1789,34 @@ void GLSLSourceEmitter::emitPreprocessorDirectivesImpl()
     // the user to specify a version as part of the target.
     m_glslExtensionTracker->requireVersion(ProfileVersion::GLSL_450);
 
-    auto requiredProfileVersion = m_glslExtensionTracker->getRequiredProfileVersion();
-    switch (requiredProfileVersion)
+    Index glslVersion = _getGLSLVersion(m_glslExtensionTracker->getRequiredProfileVersion());
+    if (glslVersion < 0)
     {
-#define CASE(TAG, VALUE)    \
-case ProfileVersion::TAG: m_writer->emit("#version " #VALUE "\n"); return
-
-        CASE(GLSL_110, 110);
-        CASE(GLSL_120, 120);
-        CASE(GLSL_130, 130);
-        CASE(GLSL_140, 140);
-        CASE(GLSL_150, 150);
-        CASE(GLSL_330, 330);
-        CASE(GLSL_400, 400);
-        CASE(GLSL_410, 410);
-        CASE(GLSL_420, 420);
-        CASE(GLSL_430, 430);
-        CASE(GLSL_440, 440);
-        CASE(GLSL_450, 450);
-        CASE(GLSL_460, 460);
-#undef CASE
+        // No information is available for us to guess a profile,
+        // so it seems like we need to pick one out of thin air.
+        //
+        // Ideally we should infer a minimum required version based
+        // on the constructs we have seen used in the user's code
+        //
+        // For now we just fall back to a reasonably recent version.
 
-        default:
-            break;
+        glslVersion = 420;
     }
 
-    // No information is available for us to guess a profile,
-    // so it seems like we need to pick one out of thin air.
-    //
-    // Ideally we should infer a minimum required version based
-    // on the constructs we have seen used in the user's code
-    //
-    // For now we just fall back to a reasonably recent version.
+    m_writer->emit("#version ");
+    m_writer->emit(glslVersion);
+    m_writer->emit("\n");
 
-    m_writer->emit("#version 420\n");
-}
+    // Output the extensions
+    if (m_glslExtensionTracker)
+    {
+        trackGLSLTargetCaps(m_glslExtensionTracker, targetReq->getTargetCaps());
+
+        StringBuilder builder;
+        m_glslExtensionTracker->appendExtensionRequireLines(builder);
+        m_writer->emit(builder.getUnownedSlice());
+    }
 
-void GLSLSourceEmitter::emitLayoutDirectivesImpl(TargetRequest* targetReq)
-{
     // Reminder: the meaning of row/column major layout
     // in our semantics is the *opposite* of what GLSL
     // calls them, because what they call "columns"
@@ -1804,16 +1824,16 @@ void GLSLSourceEmitter::emitLayoutDirectivesImpl(TargetRequest* targetReq)
     //
     switch (targetReq->getDefaultMatrixLayoutMode())
     {
-        case kMatrixLayoutMode_RowMajor:
-        default:
-            m_writer->emit("layout(column_major) uniform;\n");
-            m_writer->emit("layout(column_major) buffer;\n");
-            break;
+    case kMatrixLayoutMode_RowMajor:
+    default:
+        m_writer->emit("layout(column_major) uniform;\n");
+        m_writer->emit("layout(column_major) buffer;\n");
+        break;
 
-        case kMatrixLayoutMode_ColumnMajor:
-            m_writer->emit("layout(row_major) uniform;\n");
-            m_writer->emit("layout(row_major) buffer;\n");
-            break;
+    case kMatrixLayoutMode_ColumnMajor:
+        m_writer->emit("layout(row_major) uniform;\n");
+        m_writer->emit("layout(row_major) buffer;\n");
+        break;
     }
 }
 
diff --git a/source/slang/slang-emit-glsl.h b/source/slang/slang-emit-glsl.h
index 481efed63..3edf7bec7 100644
--- a/source/slang/slang-emit-glsl.h
+++ b/source/slang/slang-emit-glsl.h
@@ -29,8 +29,8 @@ protected:
     
     virtual void emitTextureOrTextureSamplerTypeImpl(IRTextureTypeBase*  type, char const* baseName) SLANG_OVERRIDE { _emitGLSLTextureOrTextureSamplerType(type, baseName); }
 
-    virtual void emitPreprocessorDirectivesImpl() SLANG_OVERRIDE;
-    virtual void emitLayoutDirectivesImpl(TargetRequest* targetReq) SLANG_OVERRIDE;
+    virtual void emitFrontMatterImpl(TargetRequest* targetReq) SLANG_OVERRIDE;
+
     virtual void emitRateQualifiersImpl(IRRate* rate) SLANG_OVERRIDE;
     virtual void emitInterpolationModifiersImpl(IRInst* varInst, IRType* valueType, IRVarLayout* layout) SLANG_OVERRIDE;
     virtual void emitSimpleTypeImpl(IRType* type) SLANG_OVERRIDE;
diff --git a/source/slang/slang-emit-hlsl.cpp b/source/slang/slang-emit-hlsl.cpp
index c319f2738..2d42aef83 100644
--- a/source/slang/slang-emit-hlsl.cpp
+++ b/source/slang/slang-emit-hlsl.cpp
@@ -665,20 +665,6 @@ bool HLSLSourceEmitter::tryEmitInstExprImpl(IRInst* inst, const EmitOpInfo& inOu
     return false;
 }
 
-void HLSLSourceEmitter::emitLayoutDirectivesImpl(TargetRequest* targetReq)
-{
-    switch (targetReq->getDefaultMatrixLayoutMode())
-    {
-        case kMatrixLayoutMode_RowMajor:
-        default:
-            m_writer->emit("#pragma pack_matrix(row_major)\n");
-            break;
-        case kMatrixLayoutMode_ColumnMajor:
-            m_writer->emit("#pragma pack_matrix(column_major)\n");
-            break;
-    }
-}
-
 void HLSLSourceEmitter::emitVectorTypeNameImpl(IRType* elementType, IRIntegerValue elementCount)
 {
     // In some cases we *need* to use the built-in syntax sugar for vector types,
@@ -1133,9 +1119,9 @@ void HLSLSourceEmitter::handleRequiredCapabilitiesImpl(IRInst* inst)
     }
 }
 
-void HLSLSourceEmitter::emitPreludeDirectivesImpl()
+void HLSLSourceEmitter::emitFrontMatterImpl(TargetRequest* targetReq) 
 {
-    if( m_extensionTracker->m_requiresNVAPI )
+    if (m_extensionTracker->m_requiresNVAPI)
     {
         // If the generated code includes implicit NVAPI use,
         // then we need to ensure that NVAPI support is included
@@ -1159,7 +1145,7 @@ void HLSLSourceEmitter::emitPreludeDirectivesImpl()
         // they could pass in these `#define`s using command-line
         // or API options.
         //
-        if( auto decor = m_irModule->getModuleInst()->findDecoration<IRNVAPISlotDecoration>() )
+        if (auto decor = m_irModule->getModuleInst()->findDecoration<IRNVAPISlotDecoration>())
         {
             m_writer->emit("#define NV_SHADER_EXTN_SLOT ");
             m_writer->emit(decor->getRegisterName());
@@ -1171,7 +1157,7 @@ void HLSLSourceEmitter::emitPreludeDirectivesImpl()
             // understanding of `space`s).
             //
             auto spaceName = decor->getSpaceName();
-            if( spaceName != "space0" )
+            if (spaceName != "space0")
             {
                 m_writer->emit("#define NV_SHADER_EXTN_REGISTER_SPACE ");
                 m_writer->emit(spaceName);
@@ -1179,6 +1165,19 @@ void HLSLSourceEmitter::emitPreludeDirectivesImpl()
             }
         }
     }
+
+    // Emit any layout declarations
+
+    switch (targetReq->getDefaultMatrixLayoutMode())
+    {
+    case kMatrixLayoutMode_RowMajor:
+    default:
+        m_writer->emit("#pragma pack_matrix(row_major)\n");
+        break;
+    case kMatrixLayoutMode_ColumnMajor:
+        m_writer->emit("#pragma pack_matrix(column_major)\n");
+        break;
+    }
 }
 
 void HLSLSourceEmitter::emitGlobalInstImpl(IRInst* inst)
diff --git a/source/slang/slang-emit-hlsl.h b/source/slang/slang-emit-hlsl.h
index bbd8ad15e..763b63277 100644
--- a/source/slang/slang-emit-hlsl.h
+++ b/source/slang/slang-emit-hlsl.h
@@ -32,7 +32,9 @@ protected:
     virtual void emitLayoutSemanticsImpl(IRInst* inst, char const* uniformSemanticSpelling) SLANG_OVERRIDE;
     virtual void emitParameterGroupImpl(IRGlobalParam* varDecl, IRUniformParameterGroupType* type) SLANG_OVERRIDE;
     virtual void emitEntryPointAttributesImpl(IRFunc* irFunc, IREntryPointDecoration* entryPointDecor) SLANG_OVERRIDE;
-    virtual void emitLayoutDirectivesImpl(TargetRequest* targetReq) SLANG_OVERRIDE;
+    
+    virtual void emitFrontMatterImpl(TargetRequest* targetReq) SLANG_OVERRIDE;
+
     virtual void emitRateQualifiersImpl(IRRate* rate) SLANG_OVERRIDE;
     virtual void emitSemanticsImpl(IRInst* inst) SLANG_OVERRIDE;
     virtual void emitSimpleFuncParamImpl(IRParam* param) SLANG_OVERRIDE;
@@ -49,8 +51,7 @@ protected:
     virtual void emitFuncDecorationsImpl(IRFunc* func) SLANG_OVERRIDE;
 
     virtual void handleRequiredCapabilitiesImpl(IRInst* inst) SLANG_OVERRIDE;
-    virtual void emitPreludeDirectivesImpl() SLANG_OVERRIDE;
-
+    
     virtual void emitGlobalInstImpl(IRInst* inst) SLANG_OVERRIDE;
 
     virtual void emitPostKeywordTypeAttributesImpl(IRInst* inst) SLANG_OVERRIDE;
diff --git a/source/slang/slang-emit.cpp b/source/slang/slang-emit.cpp
index baf0949bb..d231acf14 100644
--- a/source/slang/slang-emit.cpp
+++ b/source/slang/slang-emit.cpp
@@ -821,16 +821,11 @@ Result linkAndOptimizeIR(
     return SLANG_OK;
 }
 
-void trackGLSLTargetCaps(
-    GLSLExtensionTracker*   extensionTracker,
-    CapabilitySet const&    caps);
-
 SlangResult CodeGenContext::emitEntryPointsSourceFromIR(
     String&                 outSource)
 {
     outSource = String();
 
-    auto extensionTracker = getExtensionTracker();
     auto session = getSession();
     auto sink = getSink();
     auto sourceManager = getSourceManager();
@@ -950,51 +945,57 @@ SlangResult CodeGenContext::emitEntryPointsSourceFromIR(
     // Now that we've emitted the code for all the declarations in the file,
     // it is time to stitch together the final output.
 
-    sourceEmitter->emitPreludeDirectives();
-
-    if (isHeterogeneousTarget(target))
-    {
-        sourceWriter.emit(get_slang_cpp_host_prelude());
-    }
-    else
-    {
-        // If there is a prelude emit it
-        const auto& prelude = session->getPreludeForLanguage(sourceLanguage);
-        if (prelude.getLength() > 0)
-        {
-            sourceWriter.emit(prelude.getUnownedSlice());
-        }
-    }
-
     // There may be global-scope modifiers that we should emit now
     // Supress emitting line directives when emitting preprocessor directives since
     // these preprocessor directives may be required to appear in the first line
     // of the output. An example is that the "#version" line in a GLSL source must
     // appear before anything else.
     sourceWriter.supressLineDirective();
-    sourceEmitter->emitPreprocessorDirectives();
-    sourceWriter.resumeLineDirective();
+    
+    // When emitting front matter we can emit the target-language-specific directives
+    // needed to get the default matrix layout to match what was requested
+    // for the given target.
+    //
+    // Note: we do not rely on the defaults for the target language,
+    // because a user could take the HLSL/GLSL generated by Slang and pass
+    // it to another compiler with non-default options specified on
+    // the command line, leading to all kinds of trouble.
+    //
+    // TODO: We need an approach to "global" layout directives that will work
+    // in the presence of multiple modules. If modules A and B were each
+    // compiled with different assumptions about how layout is performed,
+    // then types/variables defined in those modules should be emitted in
+    // a way that is consistent with that layout...
 
-    if (auto glslExtensionTracker = as<GLSLExtensionTracker>(extensionTracker))
-    {
-        trackGLSLTargetCaps(glslExtensionTracker, targetRequest->getTargetCaps());
+    // Emit any front matter
+    sourceEmitter->emitFrontMatter(targetRequest);
 
-        StringBuilder builder;
-        glslExtensionTracker->appendExtensionRequireLines(builder);
-        sourceWriter.emit(builder.getUnownedSlice());
+    // If heterogeneous we output the prelude before everything else 
+    if (isHeterogeneousTarget(target))
+    {
+        sourceWriter.emit(get_slang_cpp_host_prelude());
+    }
+    else
+    {
+        // Get the prelude
+        String prelude = session->getPreludeForLanguage(sourceLanguage);
+        sourceWriter.emit(prelude);
     }
 
-    sourceEmitter->emitLayoutDirectives(targetRequest);
+    // Emit anything that goes before the contents of the code generated for the module
+    sourceEmitter->emitPreModule();
 
-    String prefix = sourceWriter.getContent();
-    
-    StringBuilder finalResultBuilder;
-    finalResultBuilder << prefix;
+    sourceWriter.resumeLineDirective();
+
+    // Get the content built so far from the front matter/prelude/preModule
+    // By getting in this way, the content is no longer referenced by the sourceWriter.
+    String finalResult = sourceWriter.getContentAndClear();
 
-    finalResultBuilder << code;
+    // Append the modules output code
+    finalResult.append(code);
 
     // Write out the result
-    outSource = finalResultBuilder.ProduceString();
+    outSource = finalResult;
     return SLANG_OK;
 }