Reflection: allow querying of semantics on varying input/output (#224)

This is functionality required to support a Falcor bug fix.

Most of the code to compute the right semantic name/index for a parameter was already present.
This change adds:

- Storage for semantic name/index on every `VarLayout`
  - Note: this is wasteful and should be optimized later

- A public API to query the semantic name/index
  - The contract is that this API returns `NULL` if the parameter had no semantic

- A bit of work in `parameter-binding.cpp` to attach semantics to varying input/output when traversing varying parameters.
  - Note: this is intentionally set up so that it associates semantics even with non-leaf parameters, so that an API user can query the semantic of a `struct` parameter and know that its members will be assigned sequential semantic indices from its starting value.

- Support for dumping this information in reflection tests

One notable thing that I did *not* change here is that the reflection test fixture doesn't report information on the output of an entry point, even though it really should. That should be fixed in a separate change, though, because it would affect many of the expected outputs.

1 files changed, 8 insertions, 0 deletions

diff --git a/source/slang/type-layout.h b/source/slang/type-layout.h
index 971088aac..d078d9554 100644
--- a/source/slang/type-layout.h
+++ b/source/slang/type-layout.h
@@ -218,6 +218,7 @@ typedef unsigned int VarLayoutFlags;
 enum VarLayoutFlag : VarLayoutFlags
 {
     IsRedeclaration = 1 << 0, ///< This is a redeclaration of some shader parameter
+    HasSemantic = 1 << 1,
 };
 
 // A reified layout for a particular variable, field, etc.
@@ -241,6 +242,13 @@ public:
     String  systemValueSemantic;
     int     systemValueSemanticIndex;
 
+    // General cse semantic name and index
+    // TODO: this and the system-value field are redundant
+    // TODO: the `VarLayout` type is getting bloated; we need to not store this
+    // information unless actually required.
+    String  semanticName;
+    int     semanticIndex;
+
     // The start register(s) for any resources
     struct ResourceInfo
     {