Improve NameTypes to keep reasonable names (#3977)

We only set a name now if there was no name, or the existing name
was really really long.

2 files changed, 23 insertions, 7 deletions

diff --git a/src/passes/NameTypes.cpp b/src/passes/NameTypes.cpp
index 2939f9ad5..a2c5016bc 100644
--- a/src/passes/NameTypes.cpp
+++ b/src/passes/NameTypes.cpp
@@ -21,14 +21,14 @@
 //
 // Ensures each type has a name. This can be useful for debugging.
 //
-// TODO: keep existing useful (short-enough) names, and just replace ones that
-//       are bothersome
-//
 
 using namespace std;
 
 namespace wasm {
 
+// An arbitrary limit, above which we rename types.
+static const size_t NameLenLimit = 20;
+
 struct NameTypes : public Pass {
   void run(PassRunner* runner, Module* module) override {
     // Find all the types.
@@ -36,10 +36,14 @@ struct NameTypes : public Pass {
     std::unordered_map<HeapType, Index> typeIndices;
     ModuleUtils::collectHeapTypes(*module, types, typeIndices);
 
-    // Ensure simple names.
+    // Ensure simple names. If a name already exists, and is short enough, keep
+    // it.
     size_t i = 0;
     for (auto& type : types) {
-      module->typeNames[type].name = "type$" + std::to_string(i++);
+      if (module->typeNames.count(type) == 0 ||
+          module->typeNames[type].name.size() >= NameLenLimit) {
+        module->typeNames[type].name = "type$" + std::to_string(i++);
+      }
     }
   }
 };
diff --git a/test/lit/passes/name-types.wast b/test/lit/passes/name-types.wast
index 03b775f20..197a55226 100644
--- a/test/lit/passes/name-types.wast
+++ b/test/lit/passes/name-types.wast
@@ -1,12 +1,24 @@
-;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
 ;; RUN: wasm-opt %s -all --name-types -S -o - | filecheck %s
 
 (module
+ ;; An obnoxious name that will be renamed.
  (type $obnoxious-super-long-type-name_____________________________1 (struct))
- ;; CHECK:      (func $foo (param $x (ref $type$1))
+
+ ;; A reasonable name that will be kept.
+ ;; CHECK:      (type $type$0 (func (param (ref $type$1) (ref $reasonable-name))))
+
+ ;; CHECK:      (type $type$1 (struct ))
+
+ ;; CHECK:      (type $reasonable-name (struct (field i32)))
+ (type $reasonable-name (struct (field i32)))
+
+ ;; CHECK:      (func $foo (param $x (ref $type$1)) (param $y (ref $reasonable-name))
  ;; CHECK-NEXT:  (nop)
  ;; CHECK-NEXT: )
  (func $foo
+  ;; Use the types to keep them alive.
   (param $x (ref $obnoxious-super-long-type-name_____________________________1))
+  (param $y (ref $reasonable-name))
  )
 )