dart2wasm compiles same code multiple times

[osa1]

While working on #55231 and having trouble with functions getting defined multiple times and getting defined accidentally (when calling unrelated functions) and not being compiled, I noticed that we actually compile many things multiple times. When I add debug prints to print when a function with the same name is defined again, I see thousands of duplicate definitions in the test suite. Some examples:

Initializers:

• toStringVisiting initializer
• GrowableList._emptyData initializer
• BoxedDouble._cache initializer
• BoxedDouble._cacheEvictIndex initializer

Type test functions:

• <obj> as _PendingEvents<T0>
• <obj> is num
• <obj> as double

Closures:

• generator1 closure at ...
• foo closure at ...
• createErrorStream closure at ...

Closure wrappers:

• closure wrapper at file://... trampoline
• closure wrapper at file://... trampoline
• closure wrapper at file://... trampoline
• closure wrapper at file://... trampoline

This is not an exhaustive list, there may be other kind of things that we compile multiple times.

The diff that I used to generate this output:

diff --git a/pkg/wasm_builder/lib/src/builder/functions.dart b/pkg/wasm_builder/lib/src/builder/functions.dart
index 2969a5f815f..5aa987e26f0 100644
--- a/pkg/wasm_builder/lib/src/builder/functions.dart
+++ b/pkg/wasm_builder/lib/src/builder/functions.dart
@@ -46,6 +46,15 @@ class FunctionsBuilder with Builder<ir.Functions> {
   FunctionBuilder define(ir.FunctionType type, [String? name]) {
     final function =
         FunctionBuilder(_module, ir.FinalizableIndex(), type, name);
+
+    if (name != null) {
+      for (final builder in _functionBuilders) {
+        if (builder.functionName == name) {
+          print("Generating duplicate name: $name");
+        }
+      }
+    }
+
     _functionBuilders.add(function);
     _addName(name, function);
     return function;

[osa1]

I checked a few of these. It looks like we give same names to different functions. I've checked a few closures, type checker functions, and initializer. Probably the rest are the same.