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).

8 files changed, 111 insertions, 2 deletions

diff --git a/scripts/fuzz_opt.py b/scripts/fuzz_opt.py
index a66c599bb..a0b763aab 100644
--- a/scripts/fuzz_opt.py
+++ b/scripts/fuzz_opt.py
@@ -496,6 +496,7 @@ opt_choices = [
     ["--reorder-functions"],
     ["--reorder-locals"],
     ["--flatten", "--rereloop"],
+    ["--roundtrip"],
     ["--rse"],
     ["--simplify-locals"],
     ["--simplify-locals-nonesting"],
diff --git a/src/ir/module-utils.h b/src/ir/module-utils.h
index f2fda908c..e212ae8dc 100644
--- a/src/ir/module-utils.h
+++ b/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.
diff --git a/src/passes/CMakeLists.txt b/src/passes/CMakeLists.txt
index a3dd1c26a..7ec9054d7 100644
--- a/src/passes/CMakeLists.txt
+++ b/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
diff --git a/src/passes/RoundTrip.cpp b/src/passes/RoundTrip.cpp
new file mode 100644
index 000000000..626c469d5
--- /dev/null
+++ b/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
diff --git a/src/passes/pass.cpp b/src/passes/pass.cpp
index 4b3021764..5dd39a453 100644
--- a/src/passes/pass.cpp
+++ b/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);
diff --git a/src/passes/passes.h b/src/passes/passes.h
index 98c7d374d..33a0b26da 100644
--- a/src/passes/passes.h
+++ b/src/passes/passes.h
@@ -94,6 +94,7 @@ Pass* createReorderFunctionsPass();
 Pass* createReorderLocalsPass();
 Pass* createReReloopPass();
 Pass* createRedundantSetEliminationPass();
+Pass* createRoundTripPass();
 Pass* createSafeHeapPass();
 Pass* createSimplifyLocalsPass();
 Pass* createSimplifyGlobalsPass();
diff --git a/test/passes/roundtrip.txt b/test/passes/roundtrip.txt
new file mode 100644
index 000000000..ca74a299e
--- /dev/null
+++ b/test/passes/roundtrip.txt
@@ -0,0 +1,7 @@
+(module
+ (type $0 (func))
+ (export "foo" (func $0))
+ (func $0 (; 0 ;)
+  (unreachable)
+ )
+)
diff --git a/test/passes/roundtrip.wast b/test/passes/roundtrip.wast
new file mode 100644
index 000000000..f562ba779
--- /dev/null
+++ b/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)
+  )
+)