Fix resource specialization with -embed-dxil (#4990)

* Fix resource specialization with `-embed-dxil`

fixes: #4989

Changes:
1. Before handing off to DCE an `oldFunc` which should be removed, clean up any leftover `IRKeepAliveDecoration` (else DCE won't remove our `oldFunc`s)

source/slang/slang-ir-specialize-resources.cpp

@@ -248,7 +248,11 @@ struct ResourceOutputSpecializationPass
  newFunc->removeAndDeallocate();
  // Check if `oldFunc` is the reason for failing,
  // Otherwise don't add to 'unspecializableFuncs'
- if(result == SpecializeFuncResult::ThisFuncFailed)
+ //
+ // Ensure oldFunc has uses, else, there is nothing to specialize here.
+ // If oldFunc has IRKeepAlive, this code should be assumed to have a 
+ // "dynamic" resource value.
+ if(result == SpecializeFuncResult::ThisFuncFailed && oldFunc->hasUses())
  unspecializableFuncs->add(oldFunc);
  return false;
  }
@@ -315,6 +319,11 @@ struct ResourceOutputSpecializationPass
  specializeCallSite(oldCall, newFunc, funcInfo);
  }
  specializedFuncs.add(oldFunc);
+
+ // Since we can no longer fail and we are replacing all `Func` uses, 'KeepAlive'
+ // can be removed from the oldFunc so DCE can it clean-up.
+ if(auto keepAliveDecoration = oldFunc->findDecoration<IRKeepAliveDecoration>())
+ keepAliveDecoration->removeAndDeallocate();
  return true;
  }
 

tests/library/precompiled-module-library-resource.slang

@@ -9,6 +9,11 @@ module "precompiled-module-library-resource";
 
 public struct ResourceStruct {
  public StructuredBuffer<int> buffer;
+
+ __init(StructuredBuffer<int> bufferIn)
+ {
+ buffer = bufferIn;
+ }
 };
 
 public int resource_in_parameter(StructuredBuffer<int> buffer)