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, 26 insertions, 0 deletions

diff --git a/source/slang/slang-emit-glsl.cpp b/source/slang/slang-emit-glsl.cpp
index bbd869eda..2347d086b 100644
--- a/source/slang/slang-emit-glsl.cpp
+++ b/source/slang/slang-emit-glsl.cpp
@@ -769,6 +769,16 @@ void GLSLSourceEmitter::_emitGLSLLayoutQualifiers(IRVarLayout* layout, EmitVarCh
     }
 }
 
+void GLSLSourceEmitter::_emitGLSLSubpassInputType(IRSubpassInputType* type)
+{
+    _emitGLSLTypePrefix(type->getElementType(), true);
+    m_writer->emit("subpassInput");
+    if (type->isMultisample())
+    {
+        m_writer->emit("MS");
+    }
+}
+
 void GLSLSourceEmitter::_emitGLSLTextureOrTextureSamplerType(IRTextureTypeBase*  type, char const* baseName)
 {
     if (type->getElementType()->getOp() == kIROp_HalfType)
@@ -2487,6 +2497,11 @@ void GLSLSourceEmitter::emitSimpleTypeImpl(IRType* type)
         _emitGLSLTextureOrTextureSamplerType(imageType, "image");
         return;
     }
+    else if (auto subpassType = as<IRSubpassInputType>(type))
+    {
+        _emitGLSLSubpassInputType(subpassType);
+        return;
+    }
     else if (const auto structuredBufferType = as<IRHLSLStructuredBufferTypeBase>(type))
     {
         // TODO: We desugar global variables with structured-buffer type into GLSL
@@ -2724,6 +2739,17 @@ void GLSLSourceEmitter::emitVarDecorationsImpl(IRInst* varDecl)
         break;
     }
 
+    // non raytracing decorations
+    for (auto decoration : varDecl->getDecorations())
+    {        
+        if (auto glslInputAttachment = as<IRGLSLInputAttachmentIndexDecoration>(decoration))
+        {
+            m_writer->emit(toSlice("layout(input_attachment_index = "));
+            m_writer->emit(glslInputAttachment->getIndex()->getValue());
+            m_writer->emit(toSlice(")\n"));
+        }
+    }
+
     if (varDecl->findDecoration<IRGloballyCoherentDecoration>())
     {
         m_writer->emit("coherent\n");