5 files changed, 33 insertions, 6 deletions
diff --git a/src/tools/wasm-emscripten-finalize.cpp b/src/tools/wasm-emscripten-finalize.cpp
index 8e37d60f4..eb475a73b 100644
--- a/src/tools/wasm-emscripten-finalize.cpp
+++ b/src/tools/wasm-emscripten-finalize.cpp
@@ -210,7 +210,12 @@ int main(int argc, const char* argv[]) {
 
   Module wasm;
   ModuleReader reader;
-  reader.setDWARF(DWARF);
+  // If we are not writing output then we definitely don't need to read debug
+  // info, as it does not affect the metadata we will emit. (However, if we
+  // emit output then definitely load the names section so that we roundtrip
+  // names properly.)
+  reader.setDebugInfo(writeOutput);
+  reader.setDWARF(DWARF && writeOutput);
   if (!writeOutput) {
     // If we are not writing the output then all we are doing is simple parsing
     // of metadata from global parts of the wasm such as imports and exports. In
diff --git a/src/wasm-binary.h b/src/wasm-binary.h
index 453bcb9af..1cf8186f8 100644
--- a/src/wasm-binary.h
+++ b/src/wasm-binary.h
@@ -1306,6 +1306,7 @@ class WasmBinaryBuilder {
   const std::vector<char>& input;
   std::istream* sourceMap;
   std::pair<uint32_t, Function::DebugLocation> nextDebugLocation;
+  bool debugInfo = true;
   bool DWARF = false;
   bool skipFunctionBodies = false;
 
@@ -1324,6 +1325,7 @@ public:
     : wasm(wasm), allocator(wasm.allocator), input(input), sourceMap(nullptr),
       nextDebugLocation(0, {0, 0, 0}), debugLocation() {}
 
+  void setDebugInfo(bool value) { debugInfo = value; }
   void setDWARF(bool value) { DWARF = value; }
   void setSkipFunctionBodies(bool skipFunctionBodies_) {
     skipFunctionBodies = skipFunctionBodies_;
diff --git a/src/wasm-io.h b/src/wasm-io.h
index 04fe90b51..036dc9c8c 100644
--- a/src/wasm-io.h
+++ b/src/wasm-io.h
@@ -27,8 +27,21 @@
 
 namespace wasm {
 
-class ModuleReader {
+class ModuleIOBase {
+protected:
+  bool debugInfo;
+
+public:
+  // Whether we support debug info (the names section).
+  void setDebugInfo(bool debugInfo_) { debugInfo = debugInfo_; }
+};
+
+class ModuleReader : public ModuleIOBase {
 public:
+  // Reading defaults to loading the names section. Name section info is used in
+  // various internal ways that we do not opt-in to currently.
+  ModuleReader() { setDebugInfo(true); }
+
   // If DWARF support is enabled, we track the locations of all IR nodes in
   // the binary, so that we can update DWARF sections later when writing.
   void setDWARF(bool DWARF_) { DWARF = DWARF_; }
@@ -67,16 +80,18 @@ private:
                       std::string sourceMapFilename);
 };
 
-class ModuleWriter {
+class ModuleWriter : public ModuleIOBase {
   bool binary = true;
-  bool debugInfo = false;
   std::string symbolMap;
   std::string sourceMapFilename;
   std::string sourceMapUrl;
 
 public:
+  // Writing defaults to not storing the names section. Storing it is a user-
+  // observable fact that must be opted into.
+  ModuleWriter() { setDebugInfo(false); }
+
   void setBinary(bool binary_) { binary = binary_; }
-  void setDebugInfo(bool debugInfo_) { debugInfo = debugInfo_; }
   void setSymbolMap(std::string symbolMap_) { symbolMap = symbolMap_; }
   void setSourceMapFilename(std::string sourceMapFilename_) {
     sourceMapFilename = sourceMapFilename_;
diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index 52aa4a6e0..c8568e469 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -1424,7 +1424,11 @@ void WasmBinaryBuilder::readUserSection(size_t payloadLen) {
   }
   payloadLen -= read;
   if (sectionName.equals(BinaryConsts::UserSections::Name)) {
-    readNames(payloadLen);
+    if (debugInfo) {
+      readNames(payloadLen);
+    } else {
+      pos += payloadLen;
+    }
   } else if (sectionName.equals(BinaryConsts::UserSections::TargetFeatures)) {
     readFeatures(payloadLen);
   } else if (sectionName.equals(BinaryConsts::UserSections::Dylink)) {
diff --git a/src/wasm/wasm-io.cpp b/src/wasm/wasm-io.cpp
index f2c5af6db..42eb9ab46 100644
--- a/src/wasm/wasm-io.cpp
+++ b/src/wasm/wasm-io.cpp
@@ -50,6 +50,7 @@ void ModuleReader::readBinaryData(std::vector<char>& input,
                                   std::string sourceMapFilename) {
   std::unique_ptr<std::ifstream> sourceMapStream;
   WasmBinaryBuilder parser(wasm, input);
+  parser.setDebugInfo(debugInfo);
   parser.setDWARF(DWARF);
   parser.setSkipFunctionBodies(skipFunctionBodies);
   if (sourceMapFilename.size()) {