Use informational target machine for metadata

Since there is nothing to optimise there...

Author: nagisa

src/librustc_codegen_llvm/back/write.rs

@@ -13,10 +13,8 @@ use crate::common;
 use crate::LlvmCodegenBackend;
 use rustc_codegen_ssa::back::write::{CodegenContext, ModuleConfig, run_assembler};
 use rustc_codegen_ssa::traits::*;
-use rustc::hir::def_id::LOCAL_CRATE;
 use rustc::session::config::{self, OutputType, Passes, Lto};
 use rustc::session::Session;
-use rustc::ty::TyCtxt;
 use rustc_codegen_ssa::{ModuleCodegen, CompiledModule};
 use rustc::util::common::time_ext;
 use rustc_fs_util::{path_to_c_string, link_or_copy};
@@ -82,14 +80,6 @@ pub fn write_output_file(
     }
 }
 
-pub fn create_target_machine(
-    tcx: TyCtxt<'_, '_, '_>,
-    find_features: bool,
-) -> &'static mut llvm::TargetMachine {
-    target_machine_factory(tcx.sess, tcx.backend_optimization_level(LOCAL_CRATE), find_features)()
-        .unwrap_or_else(|err| llvm_err(tcx.sess.diagnostic(), &err).raise() )
-}
-
 pub fn create_informational_target_machine(
     sess: &Session,
     find_features: bool,

src/librustc_codegen_llvm/context.rs

@@ -154,7 +154,7 @@ pub unsafe fn create_module(
 
     // Ensure the data-layout values hardcoded remain the defaults.
     if sess.target.target.options.is_builtin {
-        let tm = crate::back::write::create_target_machine(tcx, false);
+        let tm = crate::back::write::create_informational_target_machine(&tcx.sess, false);
         llvm::LLVMRustSetDataLayoutFromTargetMachine(llmod, tm);
         llvm::LLVMRustDisposeTargetMachine(tm);
 

src/librustc_codegen_llvm/lib.rs

@@ -24,7 +24,7 @@
 #![deny(rust_2018_idioms)]
 #![allow(explicit_outlives_requirements)]
 
-use back::write::create_target_machine;
+use back::write::create_informational_target_machine;
 use syntax_pos::symbol::Symbol;
 
 extern crate flate2;
@@ -114,8 +114,9 @@ pub struct LlvmCodegenBackend(());
 
 impl ExtraBackendMethods for LlvmCodegenBackend {
     fn new_metadata(&self, tcx: TyCtxt<'_, '_, '_>, mod_name: &str) -> ModuleLlvm {
-        ModuleLlvm::new(tcx, mod_name)
+        ModuleLlvm::new_metadata(tcx, mod_name)
     }
+
     fn write_metadata<'b, 'gcx>(
         &self,
         tcx: TyCtxt<'b, 'gcx, 'gcx>,
@@ -366,15 +367,14 @@ unsafe impl Send for ModuleLlvm { }
 unsafe impl Sync for ModuleLlvm { }
 
 impl ModuleLlvm {
-    fn new(tcx: TyCtxt<'_, '_, '_>, mod_name: &str) -> Self {
+    fn new_metadata(tcx: TyCtxt<'_, '_, '_>, mod_name: &str) -> Self {
         unsafe {
             let llcx = llvm::LLVMRustContextCreate(tcx.sess.fewer_names());
             let llmod_raw = context::create_module(tcx, llcx, mod_name) as *const _;
-
             ModuleLlvm {
                 llmod_raw,
                 llcx,
-                tm: create_target_machine(tcx, false),
+                tm: create_informational_target_machine(&tcx.sess, false),
             }
         }
     }

src/librustc_codegen_ssa/back/write.rs

@@ -1022,7 +1022,13 @@ fn start_executing_work<B: ExtraBackendMethods>(
         None
     };
 
-    let ol = tcx.backend_optimization_level(LOCAL_CRATE);
+    let ol = if tcx.sess.opts.debugging_opts.no_codegen
+             || !tcx.sess.opts.output_types.should_codegen() {
+        // If we know that we won’t be doing codegen, create target machines without optimisation.
+        config::OptLevel::No
+    } else {
+        tcx.backend_optimization_level(LOCAL_CRATE)
+    };
     let cgcx = CodegenContext::<B> {
         backend: backend.clone(),
         crate_types: sess.crate_types.borrow().clone(),