Add a RoundTrip pass (#2516)

This pass writes and reads the module. This shows the effects
of converting to and back from the binary format, and will be
useful in testing dwarf debug support (where we'll need to see
that writing and reading a module preserves debug info properly).

Author: kripken

scripts/fuzz_opt.py

@@ -496,6 +496,7 @@ def write_commands(commands, filename):
     ["--reorder-functions"],
     ["--reorder-locals"],
     ["--flatten", "--rereloop"],
+    ["--roundtrip"],
     ["--rse"],
     ["--simplify-locals"],
     ["--simplify-locals-nonesting"],

src/ir/module-utils.h

@@ -105,8 +105,8 @@ inline Event* copyEvent(Event* event, Module& out) {
   return ret;
 }
 
-inline void copyModule(Module& in, Module& out) {
-  // we use names throughout, not raw points, so simple copying is fine
+inline void copyModule(const Module& in, Module& out) {
+  // we use names throughout, not raw pointers, so simple copying is fine
   // for everything *but* expressions
   for (auto& curr : in.functionTypes) {
     out.addFunctionType(make_unique<FunctionType>(*curr));
@@ -136,6 +136,20 @@ inline void copyModule(Module& in, Module& out) {
   out.debugInfoFileNames = in.debugInfoFileNames;
 }
 
+inline void clearModule(Module& wasm) {
+  wasm.functionTypes.clear();
+  wasm.exports.clear();
+  wasm.functions.clear();
+  wasm.globals.clear();
+  wasm.events.clear();
+  wasm.table.segments.clear();
+  wasm.memory.segments.clear();
+  wasm.start = Name();
+  wasm.userSections.clear();
+  wasm.debugInfoFileNames.clear();
+  wasm.updateMaps();
+}
+
 // Renaming
 
 // Rename functions along with all their uses.

src/passes/CMakeLists.txt

@@ -47,6 +47,7 @@ set(passes_SOURCES
   PrintCallGraph.cpp
   PrintFeatures.cpp
   PrintFunctionMap.cpp
+  RoundTrip.cpp
   StackIR.cpp
   Strip.cpp
   StripTargetFeatures.cpp

src/passes/RoundTrip.cpp

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2019 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+//
+// Write the module to binary, and load it from there. This is useful in
+// testing to check for the effects of roundtripping in a single wasm-opt
+// parameter.
+//
+
+#ifdef _WIN32
+#include <io.h>
+#endif
+
+#include <cstdlib>
+#include <vector>
+
+#include "ir/module-utils.h"
+#include "pass.h"
+#include "support/file.h"
+#include "wasm-io.h"
+#include "wasm.h"
+
+using namespace std;
+
+namespace wasm {
+
+struct RoundTrip : public Pass {
+  void run(PassRunner* runner, Module* module) override {
+    std::string templateName = "byn_round_trip_XXXXXX";
+    std::vector<char> buffer(templateName.begin(), templateName.end());
+    buffer.push_back(0);
+#ifndef _WIN32
+    auto fd = mkstemp(buffer.data());
+    WASM_UNUSED(fd);
+    std::string tempName(buffer.begin(), buffer.end());
+#else
+    std::string tempName = _mktemp(buffer.data());
+#endif
+    // Write
+    ModuleWriter writer;
+    writer.setBinary(true);
+    writer.setDebugInfo(runner->options.debugInfo);
+    writer.write(*module, tempName);
+    // Read
+    Module newModule;
+    ModuleReader reader;
+    reader.read(tempName, newModule);
+    // Clean up
+    std::remove(tempName.c_str());
+    // Swap in
+    ModuleUtils::clearModule(*module);
+    ModuleUtils::copyModule(newModule, *module);
+  }
+};
+
+Pass* createRoundTripPass() { return new RoundTrip(); }
+
+} // namespace wasm

src/passes/pass.cpp

@@ -276,6 +276,9 @@ void PassRegistry::registerPasses() {
                createReReloopPass);
   registerPass(
     "rse", "remove redundant local.sets", createRedundantSetEliminationPass);
+  registerPass("roundtrip",
+               "write the module to binary, then read it",
+               createRoundTripPass);
   registerPass("safe-heap",
                "instrument loads and stores to check for invalid behavior",
                createSafeHeapPass);

src/passes/passes.h

@@ -94,6 +94,7 @@ Pass* createReorderFunctionsPass();
 Pass* createReorderLocalsPass();
 Pass* createReReloopPass();
 Pass* createRedundantSetEliminationPass();
+Pass* createRoundTripPass();
 Pass* createSafeHeapPass();
 Pass* createSimplifyLocalsPass();
 Pass* createSimplifyGlobalsPass();

test/passes/roundtrip.txt

@@ -0,0 +1,7 @@
+(module
+ (type $0 (func))
+ (export "foo" (func $0))
+ (func $0 (; 0 ;)
+  (unreachable)
+ )
+)

test/passes/roundtrip.wast

@@ -0,0 +1,11 @@
+(module
+  (func "foo"
+    ;; binaryen skips unreachable code while reading the binary format
+    (unreachable)
+    (nop)
+    (nop)
+    (nop)
+    (nop)
+    (nop)
+  )
+)