Revert "Use callback-based interface to load ThinLTO import data into…

… rustc."

This reverts commit e045a6c.

src/librustc_codegen_llvm/back/lto.rs

@@ -805,54 +805,66 @@ pub struct ThinLTOImports {
 
 impl ThinLTOImports {
 
-    pub fn new() -> ThinLTOImports {
+    pub fn new_empty() -> ThinLTOImports {
         ThinLTOImports {
             imports: FxHashMap(),
         }
     }
 
     /// Load the ThinLTO import map from ThinLTOData.
     unsafe fn from_thin_lto_data(data: *const llvm::ThinLTOData) -> ThinLTOImports {
+        let raw_data: *const llvm::ThinLTOModuleImports =
+            llvm::LLVMRustGetThinLTOModuleImports(data);
 
-        fn module_name_to_str(c_str: &CStr) -> &str {
-            match c_str.to_str() {
-                Ok(s) => s,
-                Err(e) => {
-                    bug!("Encountered non-utf8 LLVM module name `{}`: {}",
-                        c_str.to_string_lossy(),
-                        e)
-                }
+        assert!(!raw_data.is_null());
+
+        let mut imports = FxHashMap();
+        let mut module_ptr = raw_data;
+        let mut module_index = 0;
+
+        loop {
+            let mut entry_ptr: *const llvm::ThinLTOModuleName = *module_ptr;
+
+            if entry_ptr.is_null() {
+                break;
             }
-        }
 
-        unsafe extern "C" fn imported_module_callback(payload: *mut libc::c_void,
-                                                      importing_module_name: *const libc::c_char,
-                                                      imported_module_name: *const libc::c_char) {
-            let map = &mut* (payload as *mut ThinLTOImports);
+            let importing_module_name = CStr::from_ptr(*entry_ptr)
+                .to_str()
+                .expect("Non-utf8 LLVM module name encountered")
+                .to_owned();
+
+            entry_ptr = entry_ptr.offset(1);
 
-            let importing_module_name = CStr::from_ptr(importing_module_name);
-            let importing_module_name = module_name_to_str(&importing_module_name);
-            let imported_module_name = CStr::from_ptr(imported_module_name);
-            let imported_module_name = module_name_to_str(&imported_module_name);
+            let mut imported_modules = vec![];
 
-            if !map.imports.contains_key(importing_module_name) {
-                map.imports.insert(importing_module_name.to_owned(), vec![]);
+            loop {
+                let imported_module_name = *entry_ptr;
+
+                if imported_module_name.is_null() {
+                    break
+                }
+
+                let imported_module_name = CStr::from_ptr(imported_module_name)
+                    .to_str()
+                    .expect("Non-utf8 LLVM module name encountered")
+                    .to_owned();
+
+                imported_modules.push(imported_module_name);
+                entry_ptr = entry_ptr.offset(1);
             }
 
-            map.imports
-               .get_mut(importing_module_name)
-               .unwrap()
-               .push(imported_module_name.to_owned());
+            imports.insert(importing_module_name, imported_modules);
+
+            module_ptr = module_ptr.offset(1);
+            module_index += 1;
         }
 
-        let mut map = ThinLTOImports {
-            imports: FxHashMap(),
-        };
+        assert_eq!(module_index, imports.len());
 
-        llvm::LLVMRustGetThinLTOModuleImports(data,
-                                              imported_module_callback,
-                                              &mut map as *mut _ as *mut libc::c_void);
-        map
+        ThinLTOImports {
+            imports
+        }
     }
 
     pub fn save_to_file(&self, path: &Path) -> io::Result<()> {

src/librustc_codegen_llvm/base.rs

@@ -1360,7 +1360,7 @@ fn load_thin_lto_imports(sess: &Session) -> lto::ThinLTOImports {
     );
 
     if !path.exists() {
-        return lto::ThinLTOImports::new();
+        return lto::ThinLTOImports::new_empty();
     }
 
     match lto::ThinLTOImports::load_from_file(&path) {

src/librustc_llvm/ffi.rs

@@ -351,9 +351,10 @@ pub enum ThinLTOData {}
 /// LLVMRustThinLTOBuffer
 pub enum ThinLTOBuffer {}
 
-// LLVMRustModuleNameCallback
-pub type ThinLTOModuleNameCallback =
-    unsafe extern "C" fn(*mut c_void, *const c_char, *const c_char);
+/// LLVMRustThinLTOModuleName
+pub type ThinLTOModuleName = *const c_char;
+/// LLVMRustThinLTOModuleImports
+pub type ThinLTOModuleImports = *const ThinLTOModuleName;
 
 /// LLVMRustThinLTOModule
 #[repr(C)]
@@ -1785,9 +1786,7 @@ extern "C" {
     ) -> bool;
     pub fn LLVMRustGetThinLTOModuleImports(
         Data: *const ThinLTOData,
-        ModuleNameCallback: ThinLTOModuleNameCallback,
-        CallbackPayload: *mut c_void,
-    );
+    ) -> *const ThinLTOModuleImports;
     pub fn LLVMRustFreeThinLTOData(Data: *mut ThinLTOData);
     pub fn LLVMRustParseBitcodeForThinLTO(
         Context: ContextRef,

src/rustllvm/PassWrapper.cpp

@@ -798,6 +798,11 @@ 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
@@ -1099,28 +1104,50 @@ LLVMRustPrepareThinLTOImport(const LLVMRustThinLTOData *Data, LLVMModuleRef M) {
   return true;
 }
 
-extern "C" typedef void (*LLVMRustModuleNameCallback)(void*, // payload
-                                                      const char*, // importing module name
-                                                      const char*); // imported module name
-
-// 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();
-
-    const auto& imports = importing_module.getValue();
-
-    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());
+/// 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;
+
+  for (const auto & module : Data->ImportLists) {
+    StringRef module_id = module.getKey();
+    const auto& imports = module.getValue();
+
+    // 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];
+
+    // 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;
     }
+
+    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