Use callback-based interface to load ThinLTO import data into rustc.

src/rustllvm/PassWrapper.cpp

@@ -798,11 +798,6 @@ LLVMRustPGOAvailable() {
 #endif
 }
 
-// We encode the ThinLTO module import map as a nested null-terminated list to
-// get it into Rust.
-typedef const char* LLVMRustThinLTOModuleName;
-typedef LLVMRustThinLTOModuleName* LLVMRustThinLTOModuleImports;
-
 #if LLVM_VERSION_GE(4, 0)
 
 // Here you'll find an implementation of ThinLTO as used by the Rust compiler
@@ -1104,50 +1099,28 @@ LLVMRustPrepareThinLTOImport(const LLVMRustThinLTOData *Data, LLVMModuleRef M) {
   return true;
 }
 
-/// Converts the LLVMRustThinLTOData::ImportLists map into a nested list. The
-/// first level is a null-terminated array with an entry for each module. Each
-/// entry is a pointer that points to a null-termined array of module names. The
-/// first entry is always the name of the *importing* module, the following
-/// entries are  the names of the modules it imports from. Each module name is
-/// a regular C string.
-extern "C" LLVMRustThinLTOModuleImports*
-LLVMRustGetThinLTOModuleImports(const LLVMRustThinLTOData *Data) {
-  // Allocate number of module +1. This is a null-terminated array.
-  LLVMRustThinLTOModuleImports* thinLTOModuleImports =
-    new LLVMRustThinLTOModuleImports[Data->ImportLists.size() + 1];
-  size_t module_index = 0;
+extern "C" typedef void (*LLVMRustModuleNameCallback)(void*, // payload
+                                                      const char*, // importing module name
+                                                      const char*); // imported module name
 
-  for (const auto & module : Data->ImportLists) {
-    StringRef module_id = module.getKey();
-    const auto& imports = module.getValue();
+// Calls `module_name_callback` for each module import done by ThinLTO.
+// The callback is provided with regular null-terminated C strings.
+extern "C" void
+LLVMRustGetThinLTOModuleImports(const LLVMRustThinLTOData *data,
+                                LLVMRustModuleNameCallback module_name_callback,
+                                void* callback_payload) {
+  for (const auto& importing_module : data->ImportLists) {
+    const std::string importing_module_id = importing_module.getKey().str();
 
-    // Allocate number of imported module + 2, one extra for the name of the
-    // importing module and another one for null-termination.
-    LLVMRustThinLTOModuleImports imports_array =
-      new LLVMRustThinLTOModuleName[imports.size() + 2];
+    const auto& imports = importing_module.getValue();
 
-    // The first value is always the name of the *importing* module.
-    imports_array[0] = strndup(module_id.data(), module_id.size());
-
-    size_t imports_array_index = 1;
-    for (const auto imported_module_id : imports.keys()) {
-      // The following values are the names of the imported modules.
-      imports_array[imports_array_index] = strndup(imported_module_id.data(),
-                                                   imported_module_id.size());
-      imports_array_index += 1;
+    for (const auto& imported_module : imports) {
+      const std::string imported_module_id = imported_module.getKey().str();
+      module_name_callback(callback_payload,
+                           importing_module_id.c_str(),
+                           imported_module_id.c_str());
     }
-
-    assert(imports_array_index == imports.size() + 1);
-    imports_array[imports_array_index] = nullptr;
-
-    thinLTOModuleImports[module_index] = imports_array;
-    module_index += 1;
   }
-
-  assert(module_index == Data->ImportLists.size());
-  thinLTOModuleImports[module_index] = nullptr;
-
-  return thinLTOModuleImports;
 }
 
 // This struct and various functions are sort of a hack right now, but the