Implement 8.14-8.19 of OpenGL-GLSL specification

The following PR implements 8.14-8.19 of the [OpenGL-GLSL specification](https://registry.khronos.org/OpenGL/specs/gl/GLSLangSpec.4.60.pdf).

Fully implements all functions and built-in type's, resolves https://github.com/shader-slang/slang/issues/3692 for GLSL & SPRI-V targets.

_Notes:_
Testing Tools:
* Fragment shaders cannot test computational results. Only OpCodes are checked for proper emitting.

Implementation Notes:
* SubpassInput requires an unknown image format.
* SubpassInput is disjoint from TextureType: __SubpassImpl (.slang) & SubpassInputType (Compiler) to reduce code generation required.
* SubpassInput required an additional input layout modifier, input_attachment_index, this was added as a new parameter binding attribute. Since the following qualifiers can overlap with different resources (`layout(input_attachment_index = 0, binding = 0, set = 0)`) input_attachment_index is checked for overlapping resource bindings separately from other qualifiers with `LayoutResourceKind::InputAttachmentIndex`.
* `GLSLInputAttachmentIndexLayoutModifier` was added to enforce function parameters only accepting `in` decorated variables.
* `in` decorated variables needed to have emitting modified to allow directly emitting the variable into function calls if used as a parameter, normally Slang has a "global variable" shadow as a "global parameter" through a copy. This does not work and is solved using `GlobalVariableShadowingGlobalParameterDecoration` to build a relationship of "global variable" to "global parameter", we then resolve this relationship and replace "global variable" uses later in compile.
* `AtomicCounterMemory` memory-constraint requires `OpCapability AtomicStorage`, `AtomicStorage` is invalid for Vulkan targets. glslang outputs for `barrier`, `memoryBarrier`, and `groupMemoryBarrier` `AtomicCounterMemory` as a memory constraint. This compiles as valid SPIR-V for Vulkan since `OpCapability AtomicStorage` is not declared. This behavior of glslang is undefined as per [3.31.Capability of the SPIR-V specification](https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#_capability). We will omit `AtomicCounterMemory` from our barrier calls.

1 files changed, 31 insertions, 2 deletions

diff --git a/source/slang/slang-emit-hlsl.cpp b/source/slang/slang-emit-hlsl.cpp
index 37411c93e..120e37f09 100644
--- a/source/slang/slang-emit-hlsl.cpp
+++ b/source/slang/slang-emit-hlsl.cpp
@@ -92,6 +92,7 @@ void HLSLSourceEmitter::_emitHLSLRegisterSemantic(LayoutResourceKind kind, EmitV
         }
         break;
 
+        case LayoutResourceKind::InputAttachmentIndex:
         case LayoutResourceKind::RegisterSpace:
         case LayoutResourceKind::GenericResource:
         case LayoutResourceKind::ExistentialTypeParam:
@@ -304,6 +305,18 @@ void HLSLSourceEmitter::_emitHLSLTextureType(IRTextureTypeBase* texType)
     m_writer->emit(" >");
 }
 
+void HLSLSourceEmitter::_emitHLSLSubpassInputType(IRSubpassInputType* subpassType)
+{
+    m_writer->emit("SubpassInput");
+    if (subpassType->isMultisample())
+    {
+        m_writer->emit("MS");
+    }
+    m_writer->emit("<");
+    emitType(subpassType->getElementType());
+    m_writer->emit(">");
+}
+
 void HLSLSourceEmitter::emitLayoutSemanticsImpl(IRInst* inst, char const* uniformSemanticSpelling)
 {
     auto layout = getVarLayout(inst); 
@@ -981,6 +994,11 @@ void HLSLSourceEmitter::emitSimpleTypeImpl(IRType* type)
         _emitHLSLTextureType(imageType);
         return;
     }
+    else if (auto subpassType = as<IRSubpassInputType>(type))
+    {
+        _emitHLSLSubpassInputType(subpassType);
+        return;
+    }
     else if (auto structuredBufferType = as<IRHLSLStructuredBufferTypeBase>(type))
     {
         switch (structuredBufferType->getOp())
@@ -1246,9 +1264,20 @@ void HLSLSourceEmitter::emitMeshShaderModifiersImpl(IRInst* varInst)
 
 void HLSLSourceEmitter::emitVarDecorationsImpl(IRInst* varDecl)
 {
-    if (varDecl->findDecoration<IRGloballyCoherentDecoration>())
+    for(auto decoration : varDecl->getDecorations())
     {
-        m_writer->emit("globallycoherent\n");
+        if (as<IRGloballyCoherentDecoration>(decoration))
+        {
+            m_writer->emit("globallycoherent\n");
+            continue;
+        }
+        else if(auto glslInputAttachmentIndex = as<IRGLSLInputAttachmentIndexDecoration>(decoration))
+        {
+            m_writer->emit("[[vk::input_attachment_index(");
+            m_writer->emit(glslInputAttachmentIndex->getIndex()->getValue());
+            m_writer->emit(")]]\n");
+            continue;
+        }
     }
 }