From 8aed72eb0c06839d400d7a54d3c71fef04199fc4 Mon Sep 17 00:00:00 2001
From: Thomas Lively <tlively@google.com>
Date: Fri, 12 Sep 2025 17:17:23 -0700
Subject: [PATCH] [Experimental] Print descriptors as vtable fields

Also print exact references as inexact references. This prints modules
using custom descriptors as if they were not using custom descriptors,
making it easier to identify optimization regressions by diffing modules
before and after enabling custom descriptors.
---
 src/wasm/wasm-type.cpp | 68 +++++++++++++++++++++++-------------------
 1 file changed, 37 insertions(+), 31 deletions(-)

diff --git a/src/wasm/wasm-type.cpp b/src/wasm/wasm-type.cpp
index 34d37da50d4..b54116258e8 100644
--- a/src/wasm/wasm-type.cpp
+++ b/src/wasm/wasm-type.cpp
@@ -126,7 +126,7 @@ struct TypePrinter {
   std::ostream& print(const Field& field);
   std::ostream& print(const Signature& sig);
   std::ostream& print(const Continuation& cont);
-  std::ostream& print(const Struct& struct_,
+  std::ostream& print(HeapType type,
                       const std::unordered_map<Index, Name>& fieldNames);
   std::ostream& print(const Array& array);
 };
@@ -1656,9 +1656,9 @@ std::ostream& TypePrinter::print(Type type) {
   } else if (type.isRef()) {
     auto heapType = type.getHeapType();
     if (type.isNullable() && heapType.isBasic() && !heapType.isShared()) {
-      if (type.isExact()) {
-        os << "(exact ";
-      }
+      // if (type.isExact()) {
+      //   os << "(exact ";
+      // }
       // Print shorthands for certain basic heap types.
       switch (heapType.getBasic(Unshared)) {
         case HeapType::ext:
@@ -1707,22 +1707,22 @@ std::ostream& TypePrinter::print(Type type) {
           os << "nullexnref";
           break;
       }
-      if (type.isExact()) {
-        os << ')';
-      }
+      // if (type.isExact()) {
+      //   os << ')';
+      // }
       return os;
     }
     os << "(ref ";
     if (type.isNullable()) {
       os << "null ";
     }
-    if (type.isExact()) {
-      os << "(exact ";
-    }
+    // if (type.isExact()) {
+    //   os << "(exact ";
+    // }
     printHeapTypeName(heapType);
-    if (type.isExact()) {
-      os << ')';
-    }
+    // if (type.isExact()) {
+    //   os << ')';
+    // }
     os << ')';
   } else {
     WASM_UNREACHABLE("unexpected type");
@@ -1813,22 +1813,22 @@ std::ostream& TypePrinter::print(HeapType type) {
   if (type.isShared()) {
     os << "(shared ";
   }
-  if (auto desc = type.getDescribedType()) {
-    os << "(describes ";
-    printHeapTypeName(*desc);
-    os << ' ';
-  }
-  if (auto desc = type.getDescriptorType()) {
-    os << "(descriptor ";
-    printHeapTypeName(*desc);
-    os << ' ';
-  }
+  // if (auto desc = type.getDescribedType()) {
+  //   os << "(describes ";
+  //   printHeapTypeName(*desc);
+  //   os << ' ';
+  // }
+  // if (auto desc = type.getDescriptorType()) {
+  //   os << "(descriptor ";
+  //   printHeapTypeName(*desc);
+  //   os << ' ';
+  // }
   switch (type.getKind()) {
     case HeapTypeKind::Func:
       print(type.getSignature());
       break;
     case HeapTypeKind::Struct:
-      print(type.getStruct(), names.fieldNames);
+      print(type, names.fieldNames);
       break;
     case HeapTypeKind::Array:
       print(type.getArray());
@@ -1839,12 +1839,12 @@ std::ostream& TypePrinter::print(HeapType type) {
     case HeapTypeKind::Basic:
       WASM_UNREACHABLE("unexpected kind");
   }
-  if (type.getDescriptorType()) {
-    os << ')';
-  }
-  if (type.getDescribedType()) {
-    os << ')';
-  }
+  // if (type.getDescriptorType()) {
+  //   os << ')';
+  // }
+  // if (type.getDescribedType()) {
+  //   os << ')';
+  // }
   if (type.isShared()) {
     os << ')';
   }
@@ -1914,9 +1914,15 @@ std::ostream& TypePrinter::print(const Continuation& continuation) {
 }
 
 std::ostream&
-TypePrinter::print(const Struct& struct_,
+TypePrinter::print(HeapType type,
                    const std::unordered_map<Index, Name>& fieldNames) {
+  const auto& struct_ = type.getStruct();
   os << "(struct";
+  if (auto desc = type.getDescriptorType()) {
+    os << " (field $vtable ";
+    print(Type(*desc, NonNullable));
+    os << ')';
+  }
   for (Index i = 0; i < struct_.fields.size(); ++i) {
     // TODO: move this to the function for printing fields.
     os << " (field ";