Defer entry-point processing so that all potential uses of builtin's …

…are found before culling the unused ones

naga/src/front/spv/function.rs

@@ -292,13 +292,13 @@ impl<I: Iterator<Item = u32>> super::Frontend<I> {
         );
 
         if let Some(ep) = self.lookup_entry_point.remove(&fun_id) {
-            self.process_entry_point(module, ep, fun_id)?;
+            self.deferred_entry_points.push((ep, fun_id));
         }
 
         Ok(())
     }
 
-    fn process_entry_point(
+    pub(super) fn process_entry_point(
         &mut self,
         module: &mut crate::Module,
         ep: super::EntryPoint,

naga/src/front/spv/mod.rs

@@ -577,6 +577,9 @@ pub struct Frontend<I> {
     lookup_function_type: FastHashMap<spirv::Word, LookupFunctionType>,
     lookup_function: FastHashMap<spirv::Word, LookupFunction>,
     lookup_entry_point: FastHashMap<spirv::Word, EntryPoint>,
+    // When parsing functions, each entry point function gets an entry here so that additional
+    // processing for them can be performed after all function parsing.
+    deferred_entry_points: Vec<(EntryPoint, spirv::Word)>,
     //Note: each `OpFunctionCall` gets a single entry here, indexed by the
     // dummy `Handle<crate::Function>` of the call site.
     deferred_function_calls: Vec<spirv::Word>,
@@ -628,6 +631,7 @@ impl<I: Iterator<Item = u32>> Frontend<I> {
             lookup_function_type: FastHashMap::default(),
             lookup_function: FastHashMap::default(),
             lookup_entry_point: FastHashMap::default(),
+            deferred_entry_points: Vec::default(),
             deferred_function_calls: Vec::default(),
             dummy_functions: Arena::new(),
             function_call_graph: GraphMap::new(),
@@ -3954,7 +3958,11 @@ impl<I: Iterator<Item = u32>> Frontend<I> {
             }?;
         }
 
-        // TODO: clear unused builtin's here?
+        // Do entry point specific processing after all functions are parsed so that we can
+        // cull unused problematic builtins of gl_PerVertex.
+        for (ep, fun_id) in core::mem::take(&mut self.deferred_entry_points) {
+            self.process_entry_point(&mut module, ep, fun_id)?;
+        }
 
         log::info!("Patching...");
         {