Only keep legacy struct types from resources (#3624)

When compiling a library without 16-bit support, certain struct types
containing either min precision types or matrices must be saved in
reflection data for conversion after linking. However, this is only
necessary when the types are used by a resource.

Instead of evaluating all matrix types and saving those that meet this
criteria, only the types used by resources are evaluated and possibly
preserved. This significantly shrinks the reflection size in this case.

lib/DXIL/DxilModule.cpp

@@ -1765,20 +1765,29 @@ bool DxilModule::StripReflection() {
     // since they have not yet been converted for legacy layout.
     // Keep all structs contained in any we must keep.
     SmallStructSetVector structsToKeep;
-    SmallStructSetVector structsToRemove;
-    for (auto &item : m_pTypeSystem->GetStructAnnotationMap()) {
       SmallStructSetVector containedStructs;
-      if (!ResourceTypeRequiresTranslation(item.first, containedStructs))
-        structsToRemove.insert(item.first);
-      else
-        structsToKeep.insert(containedStructs.begin(), containedStructs.end());
+    for (auto &CBuf : GetCBuffers())
+      if (StructType *ST = dyn_cast<StructType>(CBuf->GetHLSLType()))
+        if (ResourceTypeRequiresTranslation(ST, containedStructs))
+          structsToKeep.insert(containedStructs.begin(), containedStructs.end());
+
+    for (auto &UAV : GetUAVs()) {
+      if (DXIL::IsStructuredBuffer(UAV->GetKind()))
+        if (StructType *ST = dyn_cast<StructType>(UAV->GetHLSLType()))
+          if (ResourceTypeRequiresTranslation(ST, containedStructs))
+            structsToKeep.insert(containedStructs.begin(), containedStructs.end());
     }
 
-    for (auto Ty : structsToKeep)
-      structsToRemove.remove(Ty);
-    for (auto Ty : structsToRemove) {
-      m_pTypeSystem->GetStructAnnotationMap().erase(Ty);
+    for (auto &SRV : GetSRVs()) {
+      if (SRV->IsStructuredBuffer() || SRV->IsTBuffer())
+        if (StructType *ST = dyn_cast<StructType>(SRV->GetHLSLType()))
+          if (ResourceTypeRequiresTranslation(ST, containedStructs))
+            structsToKeep.insert(containedStructs.begin(), containedStructs.end());
     }
+
+    m_pTypeSystem->GetStructAnnotationMap().remove_if([structsToKeep](
+      const std::pair<const StructType *, std::unique_ptr<DxilStructAnnotation>>
+          &I) { return !structsToKeep.count(I.first); });
   } else {
     // Remove struct annotations.
     if (!m_pTypeSystem->GetStructAnnotationMap().empty()) {