Add support for Vulkan raytraicng "shader record" (#735)

The syntax for this is a placeholder for now, since we will probably want to migrate to whatever gets decided on for dxc. To declare that some data should be part of the "shader record" use `layout(shaderRecordNV)` to mirror the GLSL raytracing extension:

```hlsl
layout(shaderRecordNV)
cbuffer MyShaderRecord
{
    float4 someColor;
    uint   someValue;
}
```

The intention (not enforced) is that an application would map `MyShaderRecord` to "root constants" in the "local root signature" when compiling for DXR, while the output code in GLSL will always map to the shader record in Vulkan raytracing:

```glsl
layout(shaderRecordNV)
buffer MyShaderRecord
{
    float4 someColor;
    uint   someValue;
};
```

This change does *not* support declaring a global value of `struct` type with `layout(shaderRecordNV)` (or a `ParameterBlock` with the modifiers, although that would be a nice-to-have feature) and it does *not* support having the contents of the shader record be mutable (even if GLSL/Vulkan allows it). Those can/should be added in future changes.

In terms of implementation, this closely mirrors the way that `layout(push_constant)` buffers were being handled, where the data inside the `ConstantBuffer<X>` (the value of type `X`) gets laid out using ordinary rules (and consuming ordinary `UNIFORM` storage, while the buffer itself is given a different layout resource to reflect that fact that it does not consume a VK `binding` any more, but a different conceptual resource.

Note: an alternative design here (that might actually be preferrable) would be to have both push-constant and shader-record buffers be handled as alternative aliases for `ConstantBuffer` (or maybe `ParameterBlock`) so that you have, e.g.:

```hlsl
PushConstantBuffer<X> myPushConstants;
ShaderRecord<Y> myShaderRecord;
```

This alternative design avoids API-specific decorations on the declarations, and reflects the intent of the programmer very directly, even when they are compiling for a target like D3D that doesn't reflect these choices at the IL level (it could still be exposed through the Slang reflection API).

6 files changed, 54 insertions, 4 deletions

diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index 187ef29bc..fb9968232 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -1753,14 +1753,14 @@ struct EmitVisitor
         emitHLSLParameterGroupFieldLayoutSemantics(&chain);
     }
 
-    void emitGLSLLayoutQualifier(
+    bool emitGLSLLayoutQualifier(
         LayoutResourceKind  kind,
         EmitVarChain*       chain)
     {
         if(!chain)
-            return;
+            return false;
         if(!chain->varLayout->FindResourceInfo(kind))
-            return;
+            return false;
 
         UInt index = getBindingOffset(chain, kind);
         UInt space = getBindingSpace(chain, kind);
@@ -1828,8 +1828,12 @@ struct EmitVisitor
         case LayoutResourceKind::PushConstantBuffer:
             Emit("layout(push_constant)\n");
             break;
+        case LayoutResourceKind::ShaderRecord:
+            Emit("layout(shaderRecordNV)\n");
+            break;
 
         }
+        return true;
     }
 
     void emitGLSLLayoutQualifiers(
@@ -5821,8 +5825,13 @@ struct EmitVisitor
 
         emitGLSLLayoutQualifier(LayoutResourceKind::DescriptorTableSlot, &containerChain);
         emitGLSLLayoutQualifier(LayoutResourceKind::PushConstantBuffer, &containerChain);
+        bool isShaderRecord = emitGLSLLayoutQualifier(LayoutResourceKind::ShaderRecord, &containerChain);
 
-        if(as<IRGLSLShaderStorageBufferType>(type))
+        if( isShaderRecord )
+        {
+            emit("buffer ");
+        }
+        else if(as<IRGLSLShaderStorageBufferType>(type))
         {
             emit("layout(std430) buffer ");
         }
diff --git a/source/slang/modifier-defs.h b/source/slang/modifier-defs.h
index e8b3f0774..2276f37f8 100644
--- a/source/slang/modifier-defs.h
+++ b/source/slang/modifier-defs.h
@@ -136,6 +136,8 @@ SIMPLE_SYNTAX_CLASS(GLSLLocalSizeXLayoutModifier,    GLSLLocalSizeLayoutModifier
 SIMPLE_SYNTAX_CLASS(GLSLLocalSizeYLayoutModifier,    GLSLLocalSizeLayoutModifier)
 SIMPLE_SYNTAX_CLASS(GLSLLocalSizeZLayoutModifier,    GLSLLocalSizeLayoutModifier)
 
+SIMPLE_SYNTAX_CLASS(ShaderRecordNVLayoutModifier, GLSLParsedLayoutModifier)
+
 // A catch-all for single-keyword modifiers
 SIMPLE_SYNTAX_CLASS(SimpleModifier, Modifier)
 
diff --git a/source/slang/parameter-binding.cpp b/source/slang/parameter-binding.cpp
index 58891a956..622474116 100644
--- a/source/slang/parameter-binding.cpp
+++ b/source/slang/parameter-binding.cpp
@@ -1184,6 +1184,13 @@ getTypeLayoutForGlobalShaderParameter_HLSL(
     auto rules = layoutContext.getRulesFamily();
     auto type = varDecl->getType();
 
+    if( varDecl->HasModifier<ShaderRecordNVLayoutModifier>() && type->As<ConstantBufferType>() )
+    {
+        return CreateTypeLayout(
+            layoutContext.with(rules->getShaderRecordConstantBufferRules()),
+            type);
+    }
+
     // We want to check for a constant-buffer type with a `push_constant` layout
     // qualifier before we move on to anything else.
     if (varDecl->HasModifier<PushConstantAttribute>() && type->As<ConstantBufferType>())
diff --git a/source/slang/parser.cpp b/source/slang/parser.cpp
index 9ccd7b962..2e0ca5df9 100644
--- a/source/slang/parser.cpp
+++ b/source/slang/parser.cpp
@@ -4562,6 +4562,7 @@ namespace Slang
                     CASE(local_size_x,  GLSLLocalSizeXLayoutModifier);
                     CASE(local_size_y,  GLSLLocalSizeYLayoutModifier);
                     CASE(local_size_z,  GLSLLocalSizeZLayoutModifier);
+                    CASE(shaderRecordNV,  ShaderRecordNVLayoutModifier);
 
                 #undef CASE
                     else
diff --git a/source/slang/type-layout.cpp b/source/slang/type-layout.cpp
index 4e9a05b53..8fc48fe4f 100644
--- a/source/slang/type-layout.cpp
+++ b/source/slang/type-layout.cpp
@@ -350,6 +350,17 @@ struct GLSLPushConstantBufferObjectLayoutRulesImpl : GLSLObjectLayoutRulesImpl
 };
 GLSLPushConstantBufferObjectLayoutRulesImpl kGLSLPushConstantBufferObjectLayoutRulesImpl_;
 
+struct GLSLShaderRecordConstantBufferObjectLayoutRulesImpl : GLSLObjectLayoutRulesImpl
+{
+    virtual SimpleLayoutInfo GetObjectLayout(ShaderParameterKind /*kind*/) override
+    {
+        // Special-case the layout for a constant-buffer, because we don't
+        // want it to allocate a descriptor-table slot
+        return SimpleLayoutInfo(LayoutResourceKind::ShaderRecord, 1);
+    }
+};
+GLSLShaderRecordConstantBufferObjectLayoutRulesImpl kGLSLShaderRecordConstantBufferObjectLayoutRulesImpl_;
+
 struct HLSLObjectLayoutRulesImpl : ObjectLayoutRulesImpl
 {
     virtual SimpleLayoutInfo GetObjectLayout(ShaderParameterKind kind) override
@@ -439,6 +450,8 @@ struct GLSLLayoutRulesFamilyImpl : LayoutRulesFamilyImpl
     LayoutRulesImpl* getRayPayloadParameterRules()      override;
     LayoutRulesImpl* getCallablePayloadParameterRules() override;
     LayoutRulesImpl* getHitAttributesParameterRules()   override;
+
+    LayoutRulesImpl* getShaderRecordConstantBufferRules() override;
 };
 
 struct HLSLLayoutRulesFamilyImpl : LayoutRulesFamilyImpl
@@ -455,6 +468,8 @@ struct HLSLLayoutRulesFamilyImpl : LayoutRulesFamilyImpl
     LayoutRulesImpl* getRayPayloadParameterRules()      override;
     LayoutRulesImpl* getCallablePayloadParameterRules() override;
     LayoutRulesImpl* getHitAttributesParameterRules()   override;
+
+    LayoutRulesImpl* getShaderRecordConstantBufferRules() override;
 };
 
 GLSLLayoutRulesFamilyImpl kGLSLLayoutRulesFamilyImpl;
@@ -475,6 +490,10 @@ LayoutRulesImpl kGLSLPushConstantLayoutRulesImpl_ = {
     &kGLSLLayoutRulesFamilyImpl, &kStd430LayoutRulesImpl, &kGLSLPushConstantBufferObjectLayoutRulesImpl_,
 };
 
+LayoutRulesImpl kGLSLShaderRecordLayoutRulesImpl_ = {
+    &kGLSLLayoutRulesFamilyImpl, &kStd430LayoutRulesImpl, &kGLSLShaderRecordConstantBufferObjectLayoutRulesImpl_,
+};
+
 LayoutRulesImpl kGLSLVaryingInputLayoutRulesImpl_ = {
     &kGLSLLayoutRulesFamilyImpl, &kGLSLVaryingInputLayoutRulesImpl, &kGLSLObjectLayoutRulesImpl,
 };
@@ -547,6 +566,11 @@ LayoutRulesImpl* GLSLLayoutRulesFamilyImpl::getPushConstantBufferRules()
     return &kGLSLPushConstantLayoutRulesImpl_;
 }
 
+LayoutRulesImpl* GLSLLayoutRulesFamilyImpl::getShaderRecordConstantBufferRules()
+{
+    return &kGLSLShaderRecordLayoutRulesImpl_;
+}
+
 LayoutRulesImpl* GLSLLayoutRulesFamilyImpl::getTextureBufferRules()
 {
     return nullptr;
@@ -606,6 +630,11 @@ LayoutRulesImpl* HLSLLayoutRulesFamilyImpl::getPushConstantBufferRules()
     return &kHLSLConstantBufferLayoutRulesImpl_;
 }
 
+LayoutRulesImpl* HLSLLayoutRulesFamilyImpl::getShaderRecordConstantBufferRules()
+{
+    return &kHLSLConstantBufferLayoutRulesImpl_;
+}
+
 LayoutRulesImpl* HLSLLayoutRulesFamilyImpl::getTextureBufferRules()
 {
     return nullptr;
diff --git a/source/slang/type-layout.h b/source/slang/type-layout.h
index 32ee41784..fa874cb80 100644
--- a/source/slang/type-layout.h
+++ b/source/slang/type-layout.h
@@ -738,6 +738,8 @@ struct LayoutRulesFamilyImpl
     virtual LayoutRulesImpl* getRayPayloadParameterRules()  = 0;
     virtual LayoutRulesImpl* getCallablePayloadParameterRules()  = 0;
     virtual LayoutRulesImpl* getHitAttributesParameterRules()= 0;
+
+    virtual LayoutRulesImpl* getShaderRecordConstantBufferRules() = 0;
 };
 
 struct TypeLayoutContext