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, 50 insertions, 5 deletions

diff --git a/source/slang/hlsl.meta.slang b/source/slang/hlsl.meta.slang
index 27ac6c415..972702170 100644
--- a/source/slang/hlsl.meta.slang
+++ b/source/slang/hlsl.meta.slang
@@ -11404,19 +11404,64 @@ ${{{{
 }
 
 //
-// Vulkan/SPIR-V specific features
+// SubpassInput
 //
 
-struct VkSubpassInput<T>
+__magic_type(SubpassInputType)
+__intrinsic_type($(kIROp_SubpassInputType))
+struct __SubpassImpl<T, let isMS:int>
 {
-    T SubpassLoad();
 }
 
-struct VkSubpassInputMS<T>
+__generic<T, let isMS:int=0>
+typealias SubpassInput = __SubpassImpl<T, isMS>;
+
+__generic<T>
+extension __SubpassImpl<T, 0>
 {
-    T SubpassLoad(int sampleIndex);
+    [ForceInline]
+    T SubpassLoad()
+    {
+        __target_switch
+        {
+        case hlsl: __intrinsic_asm "$0.SubpassLoad()";
+        case spirv:
+        {
+            let zeroVec = int2(0);
+            return spirv_asm
+            {
+                OpCapability StorageImageReadWithoutFormat;
+                result:$$T = OpImageRead $this $zeroVec
+            };
+        }
+        }
+    }
 }
 
+__generic<T, let isMS:int=1>
+typealias SubpassInputMS = __SubpassImpl<T, isMS>;
+
+__generic<T>
+extension __SubpassImpl<T, 1>
+{
+    [ForceInline]
+    T SubpassLoad(int sample)
+    {
+        __target_switch
+        {
+        case hlsl: __intrinsic_asm "$0.SubpassLoad($1)";
+        case spirv:
+        {
+            let zeroVec = int2(0);
+            return spirv_asm
+            {
+                OpCapability StorageImageReadWithoutFormat;
+                result:$$T = OpImageRead $this $zeroVec Sample $sample
+            };
+        }
+        }
+    }
+}
 
 ///
 /// Shader Execution Reordering (SER)