When legalizing, optionally export the original function too with orig$X (#2427)

The original is necessary if we want to pass it to wasm, where it will be called
directly, without JS legalization. For example the JS dynamic loader in
emscripten needs this, emscripten-core/emscripten#9562

Author: kripken

src/passes/LegalizeJSInterface.cpp

@@ -50,17 +50,42 @@ struct LegalizeJSInterface : public Pass {
   LegalizeJSInterface(bool full) : full(full) {}
 
   void run(PassRunner* runner, Module* module) override {
+    auto exportOriginals =
+      !runner->options
+         .getArgumentOrDefault("legalize-js-interface-export-originals", "")
+         .empty();
     // for each illegal export, we must export a legalized stub instead
+    std::vector<Export*> newExports;
     for (auto& ex : module->exports) {
       if (ex->kind == ExternalKind::Function) {
         // if it's an import, ignore it
         auto* func = module->getFunction(ex->value);
         if (isIllegal(func) && shouldBeLegalized(ex.get(), func)) {
+          // Provide a legal function for the export.
           auto legalName = makeLegalStub(func, module);
           ex->value = legalName;
+          if (exportOriginals) {
+            // Also export the original function, before legalization. This is
+            // not normally useful for JS, except in cases like dynamic linking
+            // where the JS loader code must copy exported wasm functions into
+            // the table, and they must not be legalized as other wasm code will
+            // do an indirect call to them. However, don't do this for imported
+            // functions, as those would be legalized in their actual module
+            // anyhow. It also makes no sense to do this for dynCalls, as they
+            // are only called from JS.
+            if (!func->imported() && !isDynCall(ex->name)) {
+              Builder builder(*module);
+              Name newName = std::string("orig$") + ex->name.str;
+              newExports.push_back(builder.makeExport(
+                newName, func->name, ExternalKind::Function));
+            }
+          }
         }
       }
     }
+    for (auto* ex : newExports) {
+      module->addExport(ex);
+    }
     // Avoid iterator invalidation later.
     std::vector<Function*> originalFunctions;
     for (auto& func : module->functions) {
@@ -136,13 +161,15 @@ struct LegalizeJSInterface : public Pass {
     return t->result == i64;
   }
 
+  bool isDynCall(Name name) { return name.startsWith("dynCall_"); }
+
   // Check if an export should be legalized.
   bool shouldBeLegalized(Export* ex, Function* func) {
     if (full) {
       return true;
     }
     // We are doing minimal legalization - just what JS needs.
-    return ex->name.startsWith("dynCall_");
+    return isDynCall(ex->name);
   }
 
   // Check if an import should be legalized.

test/passes/legalize-js-interface_pass-arg=legalize-js-interface-export-originals.txt

@@ -0,0 +1,27 @@
+(module
+ (type $FUNCSIG$j (func (result i64)))
+ (type $FUNCSIG$vi (func (param i32)))
+ (import "env" "setTempRet0" (func $setTempRet0 (param i32)))
+ (export "func" (func $legalstub$func))
+ (export "orig$func" (func $func))
+ (func $func (; 1 ;) (type $FUNCSIG$j) (result i64)
+  (unreachable)
+ )
+ (func $legalstub$func (; 2 ;) (result i32)
+  (local $0 i64)
+  (local.set $0
+   (call $func)
+  )
+  (call $setTempRet0
+   (i32.wrap_i64
+    (i64.shr_u
+     (local.get $0)
+     (i64.const 32)
+    )
+   )
+  )
+  (i32.wrap_i64
+   (local.get $0)
+  )
+ )
+)

test/passes/legalize-js-interface_pass-arg=legalize-js-interface-export-originals.wast

@@ -0,0 +1,7 @@
+(module
+  (export "func" (func $func))
+  (func $func (result i64)
+    (unreachable)
+  )
+)
+