Serialize modules into ThinBuffer after initial optimization

Instead of keeping all modules in memory until thin LTO and only
serializing them then, serialize the module immediately after
it finishes optimizing.

4 files changed, 64 insertions, 49 deletions

diff --git a/src/librustc_codegen_llvm/back/lto.rs b/src/librustc_codegen_llvm/back/lto.rs
index 5f5d0c40fe3..bddb45da10b 100644
--- a/src/librustc_codegen_llvm/back/lto.rs
+++ b/src/librustc_codegen_llvm/back/lto.rs
@@ -159,7 +159,7 @@ pub(crate) fn run_fat(cgcx: &CodegenContext<LlvmCodegenBackend>,
 /// lists, one of the modules that need optimization and another for modules that
 /// can simply be copied over from the incr. comp. cache.
 pub(crate) fn run_thin(cgcx: &CodegenContext<LlvmCodegenBackend>,
-                       modules: Vec<ModuleCodegen<ModuleLlvm>>,
+                       modules: Vec<(String, ThinBuffer)>,
                        cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
                        timeline: &mut Timeline)
     -> Result<(Vec<LtoModuleCodegen<LlvmCodegenBackend>>, Vec<WorkProduct>), FatalError>
@@ -182,6 +182,31 @@ pub(crate) fn run_thin(cgcx: &CodegenContext<LlvmCodegenBackend>,
              timeline)
 }
 
+pub(crate) fn prepare_thin(
+    cgcx: &CodegenContext<LlvmCodegenBackend>,
+    module: ModuleCodegen<ModuleLlvm>
+) -> (String, ThinBuffer) {
+    let name = module.name.clone();
+    let buffer = ThinBuffer::new(module.module_llvm.llmod());
+
+    // We emit the module after having serialized it into a ThinBuffer
+    // because only then it will contain the ThinLTO module summary.
+    if let Some(ref incr_comp_session_dir) = cgcx.incr_comp_session_dir {
+        if cgcx.config(module.kind).emit_pre_thin_lto_bc {
+            let path = incr_comp_session_dir
+                .join(pre_lto_bitcode_filename(&name));
+
+            fs::write(&path, buffer.data()).unwrap_or_else(|e| {
+                panic!("Error writing pre-lto-bitcode file `{}`: {}",
+                       path.display(),
+                       e);
+            });
+        }
+    }
+
+    (name, buffer)
+}
+
 fn fat_lto(cgcx: &CodegenContext<LlvmCodegenBackend>,
            diag_handler: &Handler,
            mut modules: Vec<ModuleCodegen<ModuleLlvm>>,
@@ -341,7 +366,7 @@ impl Drop for Linker<'a> {
 /// they all go out of scope.
 fn thin_lto(cgcx: &CodegenContext<LlvmCodegenBackend>,
             diag_handler: &Handler,
-            modules: Vec<ModuleCodegen<ModuleLlvm>>,
+            modules: Vec<(String, ThinBuffer)>,
             serialized_modules: Vec<(SerializedModule<ModuleBuffer>, CString)>,
             cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
             symbol_white_list: &[*const libc::c_char],
@@ -361,41 +386,17 @@ fn thin_lto(cgcx: &CodegenContext<LlvmCodegenBackend>,
         let mut module_names = Vec::with_capacity(full_scope_len);
         let mut thin_modules = Vec::with_capacity(full_scope_len);
 
-        // FIXME: right now, like with fat LTO, we serialize all in-memory
-        //        modules before working with them and ThinLTO. We really
-        //        shouldn't do this, however, and instead figure out how to
-        //        extract a summary from an in-memory module and then merge that
-        //        into the global index. It turns out that this loop is by far
-        //        the most expensive portion of this small bit of global
-        //        analysis!
-        for (i, module) in modules.into_iter().enumerate() {
-            info!("local module: {} - {}", i, module.name);
-            let name = CString::new(module.name.clone()).unwrap();
-            let buffer = ThinBuffer::new(module.module_llvm.llmod());
-
-            // We emit the module after having serialized it into a ThinBuffer
-            // because only then it will contain the ThinLTO module summary.
-            if let Some(ref incr_comp_session_dir) = cgcx.incr_comp_session_dir {
-                if cgcx.config(module.kind).emit_pre_thin_lto_bc {
-                    let path = incr_comp_session_dir
-                        .join(pre_lto_bitcode_filename(&module.name));
-
-                    fs::write(&path, buffer.data()).unwrap_or_else(|e| {
-                        panic!("Error writing pre-lto-bitcode file `{}`: {}",
-                               path.display(),
-                               e);
-                    });
-                }
-            }
-
+        for (i, (name, buffer)) in modules.into_iter().enumerate() {
+            info!("local module: {} - {}", i, name);
+            let cname = CString::new(name.clone()).unwrap();
             thin_modules.push(llvm::ThinLTOModule {
-                identifier: name.as_ptr(),
+                identifier: cname.as_ptr(),
                 data: buffer.data().as_ptr(),
                 len: buffer.data().len(),
             });
             thin_buffers.push(buffer);
-            module_names.push(name);
-            timeline.record(&module.name);
+            module_names.push(cname);
+            timeline.record(&name);
         }
 
         // FIXME: All upstream crates are deserialized internally in the
diff --git a/src/librustc_codegen_llvm/lib.rs b/src/librustc_codegen_llvm/lib.rs
index 4eb1fc1b1dc..ff06d3759bd 100644
--- a/src/librustc_codegen_llvm/lib.rs
+++ b/src/librustc_codegen_llvm/lib.rs
@@ -185,7 +185,7 @@ impl WriteBackendMethods for LlvmCodegenBackend {
     }
     fn run_thin_lto(
         cgcx: &CodegenContext<Self>,
-        modules: Vec<ModuleCodegen<Self::Module>>,
+        modules: Vec<(String, Self::ThinBuffer)>,
         cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
         timeline: &mut Timeline
     ) -> Result<(Vec<LtoModuleCodegen<Self>>, Vec<WorkProduct>), FatalError> {
@@ -216,6 +216,12 @@ impl WriteBackendMethods for LlvmCodegenBackend {
     ) -> Result<CompiledModule, FatalError> {
         back::write::codegen(cgcx, diag_handler, module, config, timeline)
     }
+    fn prepare_thin(
+        cgcx: &CodegenContext<Self>,
+        module: ModuleCodegen<Self::Module>
+    ) -> (String, Self::ThinBuffer) {
+        back::lto::prepare_thin(cgcx, module)
+    }
     fn run_lto_pass_manager(
         cgcx: &CodegenContext<Self>,
         module: &ModuleCodegen<Self::Module>,
diff --git a/src/librustc_codegen_ssa/back/write.rs b/src/librustc_codegen_ssa/back/write.rs
index fe40cb18483..59955ce77cd 100644
--- a/src/librustc_codegen_ssa/back/write.rs
+++ b/src/librustc_codegen_ssa/back/write.rs
@@ -253,7 +253,7 @@ impl<B: WriteBackendMethods> CodegenContext<B> {
 fn generate_lto_work<B: ExtraBackendMethods>(
     cgcx: &CodegenContext<B>,
     needs_fat_lto: Vec<ModuleCodegen<B::Module>>,
-    needs_thin_lto: Vec<ModuleCodegen<B::Module>>,
+    needs_thin_lto: Vec<(String, B::ThinBuffer)>,
     import_only_modules: Vec<(SerializedModule<B::ModuleBuffer>, WorkProduct)>
 ) -> Vec<(WorkItem<B>, u64)> {
     let mut timeline = cgcx.time_graph.as_ref().map(|tg| {
@@ -678,17 +678,17 @@ impl<B: WriteBackendMethods> WorkItem<B> {
     }
 }
 
-enum WorkItemResult<M> {
+enum WorkItemResult<B: WriteBackendMethods> {
     Compiled(CompiledModule),
-    NeedsFatLTO(ModuleCodegen<M>),
-    NeedsThinLTO(ModuleCodegen<M>),
+    NeedsFatLTO(ModuleCodegen<B::Module>),
+    NeedsThinLTO(String, B::ThinBuffer),
 }
 
 fn execute_work_item<B: ExtraBackendMethods>(
     cgcx: &CodegenContext<B>,
     work_item: WorkItem<B>,
     timeline: &mut Timeline
-) -> Result<WorkItemResult<B::Module>, FatalError> {
+) -> Result<WorkItemResult<B>, FatalError> {
     let module_config = cgcx.config(work_item.module_kind());
 
     match work_item {
@@ -716,7 +716,7 @@ fn execute_optimize_work_item<B: ExtraBackendMethods>(
     module: ModuleCodegen<B::Module>,
     module_config: &ModuleConfig,
     timeline: &mut Timeline
-) -> Result<WorkItemResult<B::Module>, FatalError> {
+) -> Result<WorkItemResult<B>, FatalError> {
     let diag_handler = cgcx.create_diag_handler();
 
     unsafe {
@@ -772,7 +772,10 @@ fn execute_optimize_work_item<B: ExtraBackendMethods>(
             };
             WorkItemResult::Compiled(module)
         }
-        ComputedLtoType::Thin => WorkItemResult::NeedsThinLTO(module),
+        ComputedLtoType::Thin => {
+            let (name, thin_buffer) = B::prepare_thin(cgcx, module);
+            WorkItemResult::NeedsThinLTO(name, thin_buffer)
+        }
         ComputedLtoType::Fat => WorkItemResult::NeedsFatLTO(module),
     })
 }
@@ -782,7 +785,7 @@ fn execute_copy_from_cache_work_item<B: ExtraBackendMethods>(
     module: CachedModuleCodegen,
     module_config: &ModuleConfig,
     _: &mut Timeline
-) -> Result<WorkItemResult<B::Module>, FatalError> {
+) -> Result<WorkItemResult<B>, FatalError> {
     let incr_comp_session_dir = cgcx.incr_comp_session_dir
                                     .as_ref()
                                     .unwrap();
@@ -844,7 +847,7 @@ fn execute_lto_work_item<B: ExtraBackendMethods>(
     mut module: lto::LtoModuleCodegen<B>,
     module_config: &ModuleConfig,
     timeline: &mut Timeline
-) -> Result<WorkItemResult<B::Module>, FatalError> {
+) -> Result<WorkItemResult<B>, FatalError> {
     let diag_handler = cgcx.create_diag_handler();
 
     unsafe {
@@ -861,7 +864,8 @@ pub enum Message<B: WriteBackendMethods> {
         worker_id: usize,
     },
     NeedsThinLTO {
-        result: ModuleCodegen<B::Module>,
+        name: String,
+        thin_buffer: B::ThinBuffer,
         worker_id: usize,
     },
     Done {
@@ -1423,10 +1427,10 @@ fn start_executing_work<B: ExtraBackendMethods>(
                     free_worker(worker_id);
                     needs_fat_lto.push(result);
                 }
-                Message::NeedsThinLTO { result, worker_id } => {
+                Message::NeedsThinLTO { name, thin_buffer, worker_id } => {
                     assert!(!started_lto);
                     free_worker(worker_id);
-                    needs_thin_lto.push(result);
+                    needs_thin_lto.push((name, thin_buffer));
                 }
                 Message::AddImportOnlyModule { module_data, work_product } => {
                     assert!(!started_lto);
@@ -1514,7 +1518,7 @@ fn spawn_work<B: ExtraBackendMethods>(
         // we exit.
         struct Bomb<B: ExtraBackendMethods> {
             coordinator_send: Sender<Box<dyn Any + Send>>,
-            result: Option<WorkItemResult<B::Module>>,
+            result: Option<WorkItemResult<B>>,
             worker_id: usize,
         }
         impl<B: ExtraBackendMethods> Drop for Bomb<B> {
@@ -1527,8 +1531,8 @@ fn spawn_work<B: ExtraBackendMethods>(
                     Some(WorkItemResult::NeedsFatLTO(m)) => {
                         Message::NeedsFatLTO::<B> { result: m, worker_id }
                     }
-                    Some(WorkItemResult::NeedsThinLTO(m)) => {
-                        Message::NeedsThinLTO::<B> { result: m, worker_id }
+                    Some(WorkItemResult::NeedsThinLTO(name, thin_buffer)) => {
+                        Message::NeedsThinLTO::<B> { name, thin_buffer, worker_id }
                     }
                     None => Message::Done::<B> { result: Err(()), worker_id }
                 };
diff --git a/src/librustc_codegen_ssa/traits/write.rs b/src/librustc_codegen_ssa/traits/write.rs
index 7b8f9395f85..edc5c2717bc 100644
--- a/src/librustc_codegen_ssa/traits/write.rs
+++ b/src/librustc_codegen_ssa/traits/write.rs
@@ -36,7 +36,7 @@ pub trait WriteBackendMethods: 'static + Sized + Clone {
     /// can simply be copied over from the incr. comp. cache.
     fn run_thin_lto(
         cgcx: &CodegenContext<Self>,
-        modules: Vec<ModuleCodegen<Self::Module>>,
+        modules: Vec<(String, Self::ThinBuffer)>,
         cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
         timeline: &mut Timeline,
     ) -> Result<(Vec<LtoModuleCodegen<Self>>, Vec<WorkProduct>), FatalError>;
@@ -60,6 +60,10 @@ pub trait WriteBackendMethods: 'static + Sized + Clone {
         config: &ModuleConfig,
         timeline: &mut Timeline,
     ) -> Result<CompiledModule, FatalError>;
+    fn prepare_thin(
+        cgcx: &CodegenContext<Self>,
+        module: ModuleCodegen<Self::Module>
+    ) -> (String, Self::ThinBuffer);
     fn run_lto_pass_manager(
         cgcx: &CodegenContext<Self>,
         llmod: &ModuleCodegen<Self::Module>,