diff --git a/src/passes/CMakeLists.txt b/src/passes/CMakeLists.txt
index 2b8790a4fae..d915c0b3fdf 100644
--- a/src/passes/CMakeLists.txt
+++ b/src/passes/CMakeLists.txt
@@ -36,6 +36,7 @@ set(passes_SOURCES
   InstrumentMemory.cpp
   LegalizeJSInterface.cpp
   LimitSegments.cpp
+  LLVM.cpp
   LocalCSE.cpp
   LogExecution.cpp
   LoopInvariantCodeMotion.cpp
diff --git a/src/passes/LLVM.cpp b/src/passes/LLVM.cpp
new file mode 100644
index 00000000000..9d4af15d331
--- /dev/null
+++ b/src/passes/LLVM.cpp
@@ -0,0 +1,182 @@
+/*
+ * Copyright 2021 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.
+ */
+
+//
+// Run LLVM to optimize the wasm.
+//
+
+#include "ir/module-utils.h"
+#include "pass.h"
+#include "support/process.h"
+#include "support/string.h"
+#include "wasm-builder.h"
+#include "wasm-io.h"
+#include "wasm.h"
+
+namespace wasm {
+
+struct LLVMOpt : public Pass {
+  void run(PassRunner* runner, Module* module) override {
+    std::string base = runner->options.getArgument(
+      "llvm-opt",
+      "LLVMOpt usage:  wasm-opt --llvm-opt=BASENAME\n"
+      "  BASENAME will be used as the base name for the temporary files that\n"
+      "  we create (BASENAME.1.wasm, BASENAME.2.c, etc.");
+
+    std::cout << "[LLVMOpt] preprocessing...\n";
+
+    // Save features, which would not otherwise make it through a round trip if
+    // the target features section has been stripped.
+    auto features = module->features;
+
+    // Note the original exports, which are the only things we will want to have
+    // exported at the end.
+    std::set<Name> originalExports;
+    for (auto& e : module->exports) {
+      originalExports.insert(e->name);
+    }
+    // We will add additional exports, some of which we can forget about
+    // imediately, but others we need to keep around until almost the very end
+    // because we need to use them.
+    // For example, we add an export for the start function if there is one, and
+    // we find it in the output wasm and use it to find the start function. We
+    // can then remove the export
+    std::set<Name> usedExports;
+
+    // Add exports for more things that we need, either for the wasm2c runtime,
+    // or to make it easy for us to find what we need afterwards. (We will
+    // remove all non-original exports at the end anyhow.)
+    Builder builder(*module);
+
+    // Ensure there is a memory.
+    module->memory.exists = true;
+    // Ensure the memory is exported, as the wasm2c runtime uses it
+    if (!module->getExportOrNull("memory")) {
+      module->addExport(
+        builder.makeExport("memory", "0", ExternalKind::Memory));
+    }
+    // Ensure a _start is exported, which wasm2c expects.
+    if (!module->getExportOrNull("_start")) {
+      Name name("byn_llvm_runtime_start");
+      module->addFunction(builder.makeFunction(
+        name, {Type::none, Type::none}, {}, builder.makeNop()));
+      module->addExport(
+        builder.makeExport("_start", name, ExternalKind::Function));
+    }
+    // Export the wasm start function, if there is one.
+    Name wasmStartExport("byn_llvm_wasm_start");
+    if (module->start.is()) {
+      module->addExport(
+        builder.makeExport(wasmStartExport, module->start, ExternalKind::Function));
+      usedExports.insert(wasmStartExport);
+    }
+
+    // Write the module to a temp file.
+    std::cout << "[LLVMOpt] writing wasm...\n";
+    std::string tempWasmA = base + ".1.wasm";
+    ModuleWriter().writeBinary(*module, tempWasmA);
+    // Compile the wasm to C, which we do by "compiling" it to wasm + wasm2c. By
+    // running emcc with --post-link, the input wasm file is left as is, and we
+    // only do the wasm2c bit.
+    std::cout << "[LLVMOpt] wasm => C...\n";
+    std::string tempWasmB = base + ".2.wasm";
+    std::string tempC = tempWasmB + ".c";
+    ProgramResult wasm2c(
+      "emcc " + tempWasmA + " -o " + tempWasmB +
+      " -s WASM2C --post-link -s ASSERTIONS=0 -s ERROR_ON_UNDEFINED_SYMBOLS=0");
+    if (wasm2c.failed()) {
+      wasm2c.dump(std::cout);
+      Fatal() << "LLVMOpt: failed to convert to C";
+    }
+    // Modify the C.
+    std::cout << "[LLVMOpt] rewrite C...\n";
+    auto cCode(read_file<std::string>(tempC, Flags::Text));
+    // Remove "static" as we want direct access to the wasm exports actually.
+    String::replaceAll(cCode, "static ", "");
+    // Remove extra sandboxing: we are compiling back to wasm!
+    String::replaceAll(cCode, "FUNC_PROLOGUE;", "");
+    String::replaceAll(cCode, "FUNC_EPILOGUE;", "");
+    Output(tempC, Flags::Text).getStream() << cCode;
+    // Compile the C to wasm.
+    std::cout << "[LLVMOpt] C => LLVM optimizer => wasm...\n";
+    std::string tempWasmC = base + ".3.wasm";
+    std::string cmd =
+      "emcc " + tempC + " -o " + tempWasmC + " -O1 -s EXPORTED_FUNCTIONS=";
+    bool first = true;
+    auto addExports = [&](const std::set<Name>& names) {
+      for (auto e : names) {
+        if (first) {
+          first = false;
+        } else {
+          cmd += ',';
+        }
+        cmd += std::string("_w2c_") + e.str;
+      }
+    };
+    addExports(originalExports);
+    addExports(usedExports);
+    ProgramResult c2wasm(cmd);
+    if (c2wasm.failed()) {
+      c2wasm.dump(std::cout);
+      Fatal() << "LLVMOpt: failed to convert to wasm";
+    }
+    // Clear the module in preparation for reading, and read it.
+    ModuleUtils::clearModule(*module);
+    std::cout << "[LLVMOpt] reading wasm...\n";
+    ModuleReader().readBinary(tempWasmC, *module);
+    // Filter out any new exports, and rename the existing ones.
+    module->exports.erase(std::remove_if(module->exports.begin(),
+                                         module->exports.end(),
+                                         [&](const std::unique_ptr<Export>& e) {
+                                           // The exports we want to erase are
+                                           // all those that are not one of our
+                                           // original exports, whose name is
+                                           // now "w2c_${ORIGINAL_NAME}"
+                                           if (!e->name.startsWith("w2c_")) {
+                                             return true;
+                                           }
+                                           e->name = e->name.str + 4;
+                                           return false;
+                                         }),
+                          module->exports.end());
+    module->updateMaps();
+    // Find the important things we exported so that we could find them later.
+    if (auto* e = module->getExportOrNull(wasmStartExport)) {
+      module->start = e->value;
+    }
+    // Remove the table: the "native" table contains things the new sandboxing
+    // layer in C added and needs. We want to look into the wasm in that
+    // sandbox.
+    // TODO: find the sandboxed table items (export them first)
+    module->tables.clear();
+    module->elementSegments.clear();
+    module->updateMaps();
+    // Do a cleanup (we may optimize anyhow, though?)
+    {
+      std::cout << "[LLVMOpt] postprocessing...\n";
+      PassRunner postRunner(runner);
+      postRunner.add("remove-unused-module-elements");
+      postRunner.setIsNested(true);
+      postRunner.run();
+    }
+    // Reapply features
+    module->features = features;
+  }
+};
+
+Pass* createLLVMOptPass() { return new LLVMOpt(); }
+
+} // namespace wasm
diff --git a/src/passes/pass.cpp b/src/passes/pass.cpp
index 89b3672729b..d38ce3b0fb5 100644
--- a/src/passes/pass.cpp
+++ b/src/passes/pass.cpp
@@ -165,6 +165,7 @@ void PassRegistry::registerPasses() {
                "legalizes i64 types on the import/export boundary in a minimal "
                "manner, only on things only JS will call",
                createLegalizeJSInterfaceMinimallyPass);
+  registerPass("llvm-opt", "run the LLVM optimizer (!)", createLLVMOptPass);
   registerPass("local-cse",
                "common subexpression elimination inside basic blocks",
                createLocalCSEPass);
diff --git a/src/passes/passes.h b/src/passes/passes.h
index 4cc8040a4e0..db1d9a6057b 100644
--- a/src/passes/passes.h
+++ b/src/passes/passes.h
@@ -61,6 +61,7 @@ Pass* createLocalCSEPass();
 Pass* createLogExecutionPass();
 Pass* createInstrumentLocalsPass();
 Pass* createInstrumentMemoryPass();
+Pass* createLLVMOptPass();
 Pass* createLoopInvariantCodeMotionPass();
 Pass* createMemory64LoweringPass();
 Pass* createMemoryPackingPass();
diff --git a/src/support/process.h b/src/support/process.h
new file mode 100644
index 00000000000..029f0af9fbe
--- /dev/null
+++ b/src/support/process.h
@@ -0,0 +1,214 @@
+/*
+ * Copyright 2021 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.
+ */
+
+//
+// Process helpers.
+//
+
+#ifndef wasm_support_process_h
+#define wasm_support_process_h
+
+#include <iostream>
+#include <string>
+
+#include "support/timing.h"
+
+#ifdef _WIN32
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif
+#include <windows.h>
+// Create a string with last error message
+std::string GetLastErrorStdStr() {
+  DWORD error = GetLastError();
+  if (error) {
+    LPVOID lpMsgBuf;
+    DWORD bufLen = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
+                                   FORMAT_MESSAGE_FROM_SYSTEM |
+                                   FORMAT_MESSAGE_IGNORE_INSERTS,
+                                 NULL,
+                                 error,
+                                 MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+                                 (LPTSTR)&lpMsgBuf,
+                                 0,
+                                 NULL);
+    if (bufLen) {
+      LPCSTR lpMsgStr = (LPCSTR)lpMsgBuf;
+      std::string result(lpMsgStr, lpMsgStr + bufLen);
+      LocalFree(lpMsgBuf);
+      return result;
+    }
+  }
+  return std::string();
+}
+#endif
+
+namespace wasm {
+
+struct ProgramResult {
+  size_t timeout;
+
+  std::string command;
+
+  int code;
+  std::string output;
+  double time;
+
+  ProgramResult(size_t timeout = -1) : timeout(timeout) {}
+  ProgramResult(std::string command, size_t timeout = -1) : timeout(timeout) {
+    getFromExecution(command);
+  }
+
+#ifdef _WIN32
+  void getFromExecution(std::string command_) {
+    command = command_;
+
+    Timer timer;
+    timer.start();
+    SECURITY_ATTRIBUTES saAttr;
+    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
+    saAttr.bInheritHandle = TRUE;
+    saAttr.lpSecurityDescriptor = NULL;
+
+    HANDLE hChildStd_OUT_Rd;
+    HANDLE hChildStd_OUT_Wr;
+
+    if (
+      // Create a pipe for the child process's STDOUT.
+      !CreatePipe(&hChildStd_OUT_Rd, &hChildStd_OUT_Wr, &saAttr, 0) ||
+      // Ensure the read handle to the pipe for STDOUT is not inherited.
+      !SetHandleInformation(hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0)) {
+      Fatal() << "CreatePipe \"" << command
+              << "\" failed: " << GetLastErrorStdStr() << ".\n";
+    }
+
+    STARTUPINFO si;
+    PROCESS_INFORMATION pi;
+
+    ZeroMemory(&si, sizeof(si));
+    si.cb = sizeof(si);
+    si.hStdError = hChildStd_OUT_Wr;
+    si.hStdOutput = hChildStd_OUT_Wr;
+    si.dwFlags |= STARTF_USESTDHANDLES;
+    ZeroMemory(&pi, sizeof(pi));
+
+    // Start the child process.
+    if (!CreateProcess(NULL, // No module name (use command line)
+                       (LPSTR)command.c_str(), // Command line
+                       NULL,                   // Process handle not inheritable
+                       NULL,                   // Thread handle not inheritable
+                       TRUE,                   // Set handle inheritance to TRUE
+                       0,                      // No creation flags
+                       NULL,                   // Use parent's environment block
+                       NULL, // Use parent's starting directory
+                       &si,  // Pointer to STARTUPINFO structure
+                       &pi)  // Pointer to PROCESS_INFORMATION structure
+    ) {
+      Fatal() << "CreateProcess \"" << command
+              << "\" failed: " << GetLastErrorStdStr() << ".\n";
+    }
+
+    // Wait until child process exits.
+    DWORD retVal = WaitForSingleObject(pi.hProcess, timeout * 1000);
+    if (retVal == WAIT_TIMEOUT) {
+      printf("Command timeout: %s", command.c_str());
+      TerminateProcess(pi.hProcess, -1);
+    }
+    DWORD dwordExitCode;
+    if (!GetExitCodeProcess(pi.hProcess, &dwordExitCode)) {
+      Fatal() << "GetExitCodeProcess failed: " << GetLastErrorStdStr() << ".\n";
+    }
+    code = (int)dwordExitCode;
+
+    // Close process and thread handles.
+    CloseHandle(pi.hProcess);
+    CloseHandle(pi.hThread);
+
+    // Read output from the child process's pipe for STDOUT
+    // Stop when there is no more data.
+    {
+      const int BUFSIZE = 4096;
+      DWORD dwRead, dwTotal, dwTotalRead = 0;
+      CHAR chBuf[BUFSIZE];
+      BOOL bSuccess = FALSE;
+
+      PeekNamedPipe(hChildStd_OUT_Rd, NULL, 0, NULL, &dwTotal, NULL);
+      while (dwTotalRead < dwTotal) {
+        bSuccess =
+          ReadFile(hChildStd_OUT_Rd, chBuf, BUFSIZE - 1, &dwRead, NULL);
+        if (!bSuccess || dwRead == 0)
+          break;
+        chBuf[dwRead] = 0;
+        dwTotalRead += dwRead;
+        output.append(chBuf);
+      }
+    }
+    timer.stop();
+    time = timer.getTotal();
+  }
+#else  // POSIX
+  // runs the command and notes the output
+  // TODO: also stderr, not just stdout?
+  void getFromExecution(std::string command_) {
+    command = command_;
+
+    Timer timer;
+    timer.start();
+    // do this using just core stdio.h and stdlib.h, for portability
+    // sadly this requires two invokes
+    code = system(("timeout " + std::to_string(timeout) + "s " + command +
+                   " > /dev/null 2> /dev/null")
+                    .c_str());
+    const int MAX_BUFFER = 1024;
+    char buffer[MAX_BUFFER];
+    FILE* stream = popen(
+      ("timeout " + std::to_string(timeout) + "s " + command + " 2> /dev/null")
+        .c_str(),
+      "r");
+    while (fgets(buffer, MAX_BUFFER, stream) != NULL) {
+      output.append(buffer);
+    }
+    pclose(stream);
+    timer.stop();
+    time = timer.getTotal() / 2;
+  }
+#endif // _WIN32
+
+  bool operator==(ProgramResult& other) {
+    return code == other.code && output == other.output;
+  }
+  bool operator!=(ProgramResult& other) { return !(*this == other); }
+
+  bool failed() { return code != 0; }
+
+  void dump(std::ostream& o) {
+    o << "[ProgramResult " << command << "]\ncode: " << code << ", stdout: \n"
+      << output << "[====]\nin " << time << " seconds\n[/ProgramResult]\n";
+  }
+};
+
+} // namespace wasm
+
+namespace std {
+
+inline std::ostream& operator<<(std::ostream& o, wasm::ProgramResult& result) {
+  result.dump(o);
+  return o;
+}
+
+} // namespace std
+
+#endif // wasm_support_process_h
diff --git a/src/support/string.h b/src/support/string.h
index 120835b80d3..bee8b0b7aa0 100644
--- a/src/support/string.h
+++ b/src/support/string.h
@@ -120,6 +120,15 @@ inline bool isNumber(const std::string& str) {
   return !str.empty() && std::all_of(str.begin(), str.end(), ::isdigit);
 }
 
+inline void
+replaceAll(std::string& str, const std::string& from, const std::string& to) {
+  size_t start = 0;
+  while ((start = str.find(from, start)) != std::string::npos) {
+    str.replace(start, from.length(), to);
+    start += to.length();
+  }
+}
+
 } // namespace String
 
 } // namespace wasm
diff --git a/src/tools/wasm-reduce.cpp b/src/tools/wasm-reduce.cpp
index 48435fac0d3..e9bc3d29f20 100644
--- a/src/tools/wasm-reduce.cpp
+++ b/src/tools/wasm-reduce.cpp
@@ -36,39 +36,12 @@
 #include "support/command-line.h"
 #include "support/file.h"
 #include "support/path.h"
+#include "support/process.h"
 #include "support/timing.h"
 #include "wasm-builder.h"
 #include "wasm-io.h"
 #include "wasm-validator.h"
-#ifdef _WIN32
-#ifndef NOMINMAX
-#define NOMINMAX
-#endif
-#include <windows.h>
-// Create a string with last error message
-std::string GetLastErrorStdStr() {
-  DWORD error = GetLastError();
-  if (error) {
-    LPVOID lpMsgBuf;
-    DWORD bufLen = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
-                                   FORMAT_MESSAGE_FROM_SYSTEM |
-                                   FORMAT_MESSAGE_IGNORE_INSERTS,
-                                 NULL,
-                                 error,
-                                 MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
-                                 (LPTSTR)&lpMsgBuf,
-                                 0,
-                                 NULL);
-    if (bufLen) {
-      LPCSTR lpMsgStr = (LPCSTR)lpMsgBuf;
-      std::string result(lpMsgStr, lpMsgStr + bufLen);
-      LocalFree(lpMsgBuf);
-      return result;
-    }
-  }
-  return std::string();
-}
-#endif
+
 using namespace wasm;
 
 // A timeout on every execution of the command.
@@ -78,148 +51,8 @@ static size_t timeout = 2;
 // default of enabling all features should work in most cases.
 static std::string extraFlags = "-all";
 
-struct ProgramResult {
-  int code;
-  std::string output;
-  double time;
-
-  ProgramResult() = default;
-  ProgramResult(std::string command) { getFromExecution(command); }
-
-#ifdef _WIN32
-  void getFromExecution(std::string command) {
-    Timer timer;
-    timer.start();
-    SECURITY_ATTRIBUTES saAttr;
-    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
-    saAttr.bInheritHandle = TRUE;
-    saAttr.lpSecurityDescriptor = NULL;
-
-    HANDLE hChildStd_OUT_Rd;
-    HANDLE hChildStd_OUT_Wr;
-
-    if (
-      // Create a pipe for the child process's STDOUT.
-      !CreatePipe(&hChildStd_OUT_Rd, &hChildStd_OUT_Wr, &saAttr, 0) ||
-      // Ensure the read handle to the pipe for STDOUT is not inherited.
-      !SetHandleInformation(hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0)) {
-      Fatal() << "CreatePipe \"" << command
-              << "\" failed: " << GetLastErrorStdStr() << ".\n";
-    }
-
-    STARTUPINFO si;
-    PROCESS_INFORMATION pi;
-
-    ZeroMemory(&si, sizeof(si));
-    si.cb = sizeof(si);
-    si.hStdError = hChildStd_OUT_Wr;
-    si.hStdOutput = hChildStd_OUT_Wr;
-    si.dwFlags |= STARTF_USESTDHANDLES;
-    ZeroMemory(&pi, sizeof(pi));
-
-    // Start the child process.
-    if (!CreateProcess(NULL, // No module name (use command line)
-                       (LPSTR)command.c_str(), // Command line
-                       NULL,                   // Process handle not inheritable
-                       NULL,                   // Thread handle not inheritable
-                       TRUE,                   // Set handle inheritance to TRUE
-                       0,                      // No creation flags
-                       NULL,                   // Use parent's environment block
-                       NULL, // Use parent's starting directory
-                       &si,  // Pointer to STARTUPINFO structure
-                       &pi)  // Pointer to PROCESS_INFORMATION structure
-    ) {
-      Fatal() << "CreateProcess \"" << command
-              << "\" failed: " << GetLastErrorStdStr() << ".\n";
-    }
-
-    // Wait until child process exits.
-    DWORD retVal = WaitForSingleObject(pi.hProcess, timeout * 1000);
-    if (retVal == WAIT_TIMEOUT) {
-      printf("Command timeout: %s", command.c_str());
-      TerminateProcess(pi.hProcess, -1);
-    }
-    DWORD dwordExitCode;
-    if (!GetExitCodeProcess(pi.hProcess, &dwordExitCode)) {
-      Fatal() << "GetExitCodeProcess failed: " << GetLastErrorStdStr() << ".\n";
-    }
-    code = (int)dwordExitCode;
-
-    // Close process and thread handles.
-    CloseHandle(pi.hProcess);
-    CloseHandle(pi.hThread);
-
-    // Read output from the child process's pipe for STDOUT
-    // Stop when there is no more data.
-    {
-      const int BUFSIZE = 4096;
-      DWORD dwRead, dwTotal, dwTotalRead = 0;
-      CHAR chBuf[BUFSIZE];
-      BOOL bSuccess = FALSE;
-
-      PeekNamedPipe(hChildStd_OUT_Rd, NULL, 0, NULL, &dwTotal, NULL);
-      while (dwTotalRead < dwTotal) {
-        bSuccess =
-          ReadFile(hChildStd_OUT_Rd, chBuf, BUFSIZE - 1, &dwRead, NULL);
-        if (!bSuccess || dwRead == 0)
-          break;
-        chBuf[dwRead] = 0;
-        dwTotalRead += dwRead;
-        output.append(chBuf);
-      }
-    }
-    timer.stop();
-    time = timer.getTotal();
-  }
-#else  // POSIX
-  // runs the command and notes the output
-  // TODO: also stderr, not just stdout?
-  void getFromExecution(std::string command) {
-    Timer timer;
-    timer.start();
-    // do this using just core stdio.h and stdlib.h, for portability
-    // sadly this requires two invokes
-    code = system(("timeout " + std::to_string(timeout) + "s " + command +
-                   " > /dev/null 2> /dev/null")
-                    .c_str());
-    const int MAX_BUFFER = 1024;
-    char buffer[MAX_BUFFER];
-    FILE* stream = popen(
-      ("timeout " + std::to_string(timeout) + "s " + command + " 2> /dev/null")
-        .c_str(),
-      "r");
-    while (fgets(buffer, MAX_BUFFER, stream) != NULL) {
-      output.append(buffer);
-    }
-    pclose(stream);
-    timer.stop();
-    time = timer.getTotal() / 2;
-  }
-#endif // _WIN32
-
-  bool operator==(ProgramResult& other) {
-    return code == other.code && output == other.output;
-  }
-  bool operator!=(ProgramResult& other) { return !(*this == other); }
-
-  bool failed() { return code != 0; }
-
-  void dump(std::ostream& o) {
-    o << "[ProgramResult] code: " << code << " stdout: \n"
-      << output << "[====]\nin " << time << " seconds\n[/ProgramResult]\n";
-  }
-};
-
-namespace std {
-
-inline std::ostream& operator<<(std::ostream& o, ProgramResult& result) {
-  result.dump(o);
-  return o;
-}
-
-} // namespace std
-
-ProgramResult expected;
+// The expected outcome.
+static ProgramResult expected;
 
 // Removing functions is extremely beneficial and efficient. We aggressively
 // try to remove functions, unless we've seen they can't be removed, in which
@@ -296,12 +129,12 @@ struct Reducer
         if (verbose) {
           std::cerr << "|    trying pass command: " << currCommand << "\n";
         }
-        if (!ProgramResult(currCommand).failed()) {
+        if (!ProgramResult(currCommand, timeout).failed()) {
           auto newSize = file_size(test);
           if (newSize < oldSize) {
             // the pass didn't fail, and the size looks smaller, so promising
             // see if it is still has the property we are preserving
-            if (ProgramResult(command) == expected) {
+            if (ProgramResult(command, timeout) == expected) {
               std::cerr << "|    command \"" << currCommand
                         << "\" succeeded, reduced size to " << newSize << '\n';
               copy_file(test, working);
@@ -1273,14 +1106,14 @@ int main(int argc, const char* argv[]) {
       std::ofstream dst(test, std::ios::binary);
       dst << "waka waka\n";
     }
-    ProgramResult resultOnInvalid(command);
+    ProgramResult resultOnInvalid(command, timeout);
     if (resultOnInvalid == expected) {
       // Try it on a valid input.
       Module emptyModule;
       ModuleWriter writer;
       writer.setBinary(true);
       writer.write(emptyModule, test);
-      ProgramResult resultOnValid(command);
+      ProgramResult resultOnValid(command, timeout);
       if (resultOnValid == expected) {
         Fatal()
           << "running the command on the given input gives the same result as "
@@ -1300,11 +1133,11 @@ int main(int argc, const char* argv[]) {
     if (!binary) {
       cmd += " -S ";
     }
-    ProgramResult readWrite(cmd);
+    ProgramResult readWrite(cmd, timeout);
     if (readWrite.failed()) {
       stopIfNotForced("failed to read and write the binary", readWrite);
     } else {
-      ProgramResult result(command);
+      ProgramResult result(command, timeout);
       if (result != expected) {
         stopIfNotForced("running command on the canonicalized module should "
                         "give the same results",
diff --git a/test/passes/llvm.passes b/test/passes/llvm.passes
new file mode 100644
index 00000000000..1b301176f47
--- /dev/null
+++ b/test/passes/llvm.passes
@@ -0,0 +1 @@
+llvm-opt=foo
diff --git a/test/passes/llvm.txt b/test/passes/llvm.txt
new file mode 100644
index 00000000000..f5dc878b407
--- /dev/null
+++ b/test/passes/llvm.txt
@@ -0,0 +1,26 @@
+[LLVMOpt] preprocessing...
+[LLVMOpt] writing wasm...
+[LLVMOpt] wasm => C...
+[LLVMOpt] rewrite C...
+[LLVMOpt] C => LLVM optimizer => wasm...
+[LLVMOpt] reading wasm...
+[LLVMOpt] postprocessing...
+(module
+ (type $none_=>_i32 (func (result i32)))
+ (type $none_=>_none (func))
+ (memory $0 256 256)
+ (data (i32.const 1024) "-+   0X0x\00(null)\00[wasm trap %d, halting]\n\00\00\00\00\00\00\00\11\00\n\00\11\11\11\00\00\00\00\05\00\00\00\00\00\00\t\00\00\00\00\0b\00\00\00\00\00\00\00\00\11\00\0f\n\11\11\11\03\n\07\00\01\00\t\0b\0b\00\00\t\06\0b\00\00\0b\00\06\11\00\00\00\11\11\11\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\0b\00\00\00\00\00\00\00\00\11\00\n\n\11\11\11\00\n\00\00\02\00\t\0b\00\00\00\t\00\0b\00\00\0b\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\0c\00\00\00\00\00\00\00\00\00\00\00\0c\00\00\00\00\0c\00\00\00\00\t\0c\00\00\00\00\00\0c\00\00\0c\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\0e\00\00\00\00\00\00\00\00\00\00\00\0d\00\00\00\04\0d\00\00\00\00\t\0e\00\00\00\00\00\0e\00\00\0e\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\10\00\00\00\00\00\00\00\00\00\00\00\0f\00\00\00\00\0f\00\00\00\00\t\10\00\00\00\00\00\10\00\00\10\00\00\12\00\00\00\12\12\12\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\12\00\00\00\12\12\12\00\00\00\00\00\00\t\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\0b\00\00\00\00\00\00\00\00\00\00\00\n\00\00\00\00\n\00\00\00\00\t\0b\00\00\00\00\00\0b\00\00\0b\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\0c\00\00\00\00\00\00\00\00\00\00\00\0c\00\00\00\00\0c\00\00\00\00\t\0c\00\00\00\00\00\0c\00\00\0c\00\000123456789ABCDEF\18\06\00\00")
+ (data (i32.const 1560) "\05\00\00\00\00\00\00\00\00\00\00\00\08\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\t\00\00\00\n\00\00\00\98\18\00\00\00\04\00\00\00\00\00\00\00\00\00\00\01\00\00\00\00\00\00\00\00\00\00\00\00\00\00\n\ff\ff\ff\ff\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\18\06\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\c0\1c\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\f0\1eP\00")
+ (export "foo" (func $2))
+ (export "byn_llvm_wasm_start" (func $3))
+ (start $3)
+ (func $2 (result i32)
+  (i32.const 42)
+ )
+ (func $3
+  (i32.store offset=1960
+   (i32.const 0)
+   (i32.const 2)
+  )
+ )
+)
diff --git a/test/passes/llvm.wast b/test/passes/llvm.wast
new file mode 100644
index 00000000000..6f57a01db23
--- /dev/null
+++ b/test/passes/llvm.wast
@@ -0,0 +1,23 @@
+(module
+ (import "env" "importedf" (func $imported-func))
+ (global $global (mut i32) (i32.const 1))
+ (start $startey)
+ (export "foo" (func $foobar))
+ (export "ex_of_im" (func $wrapped_imported_func))
+ (func $foobar (result i32)
+  (i32.add
+   (i32.const 41)
+   (i32.const 1)
+  )
+ )
+ (func $startey
+  ;; TODO: otpimize globals
+  (global.set $global
+   (i32.const 2)
+  )
+  (call $imported-func)
+ )
+ (func $wrapped_imported_func
+  (call $imported-func)
+ )
+)