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, 30 insertions, 5 deletions

diff --git a/source/slang/slang-parameter-binding.cpp b/source/slang/slang-parameter-binding.cpp
index 01b7f6724..6725380f2 100644
--- a/source/slang/slang-parameter-binding.cpp
+++ b/source/slang/slang-parameter-binding.cpp
@@ -1072,14 +1072,35 @@ static void addExplicitParameterBindings_GLSL(
     semanticInfo.index = 0;
     semanticInfo.space = 0;
 
+    LayoutSemanticInfo subpassSemanticInfo;
+    bool foundBinding = false;
+    bool foundSubpass = false;
+
     if( (foundResInfo = typeLayout->FindResourceInfo(LayoutResourceKind::DescriptorTableSlot)) != nullptr )
     {
-        // Try to find `binding` and `set`
-        if (auto attr = varDecl.getDecl()->findModifier<GLSLBindingAttribute>())
+        for (auto dec : varDecl.getDecl()->modifiers)
         {
-            resInfo = foundResInfo;
-            semanticInfo.index = attr->binding;
-            semanticInfo.space = attr->set;
+            // Try to find `binding` and `set`
+            if (auto glslBindingAttr = as<GLSLBindingAttribute>(dec))
+            {
+                resInfo = foundResInfo;
+                semanticInfo.index = glslBindingAttr->binding;
+                semanticInfo.space = glslBindingAttr->set;
+                foundBinding = true;
+                if (foundSubpass) 
+                    break;
+            }
+            // Try to find `input_attachment_index`
+            else if (auto glslAttachmentIndexAttr = as<GLSLInputAttachmentIndexLayoutModifier>(dec))
+            {
+                // Subpass fills semantic info of a descriptor & subpass
+                subpassSemanticInfo.index = stringToInt(glslAttachmentIndexAttr->valToken.getContent());
+                subpassSemanticInfo.space = 0;
+                subpassSemanticInfo.kind = LayoutResourceKind::InputAttachmentIndex;
+                foundSubpass = true;
+                if (foundBinding) 
+                    break;
+            }
         }
     }
     else if( (foundResInfo = typeLayout->FindResourceInfo(LayoutResourceKind::SubElementRegisterSpace)) != nullptr )
@@ -1113,6 +1134,9 @@ static void addExplicitParameterBindings_GLSL(
         semanticInfo.kind = kind;
 
         addExplicitParameterBinding(context, parameterInfo, varDecl.getDecl(), semanticInfo, count);
+        if (foundSubpass)
+            addExplicitParameterBinding(context, parameterInfo, varDecl.getDecl(), subpassSemanticInfo, count);
+
         return;
     }
 
@@ -2066,6 +2090,7 @@ static RefPtr<TypeLayout> processEntryPointVaryingParameter(
         return arrayTypeLayout;
     }
     // Ignore a bunch of types that don't make sense here...
+    else if (const auto subpassType = as<SubpassInputType>(type)) { return nullptr;  }
     else if (const auto textureType = as<TextureType>(type)) { return nullptr;  }
     else if(const auto samplerStateType = as<SamplerStateType>(type)) { return nullptr;  }
     else if(const auto constantBufferType = as<ConstantBufferType>(type)) { return nullptr;  }