Add config option

Author: nikic

src/librustc_codegen_llvm/back/write.rs

@@ -339,8 +339,7 @@ pub(crate) unsafe fn optimize(
     }
 
     if let Some(opt_level) = config.opt_level {
-        let use_new_pm = true;
-        if use_new_pm {
+        if config.new_llvm_pass_manager {
             let unroll_loops =
                 opt_level != config::OptLevel::Size && opt_level != config::OptLevel::SizeMin;
             let prepare_for_thin_lto = cgcx.lto == Lto::Thin

src/librustc_codegen_ssa/back/write.rs

@@ -85,6 +85,7 @@ pub struct ModuleConfig {
     pub vectorize_slp: bool,
     pub merge_functions: bool,
     pub inline_threshold: Option<usize>,
+    pub new_llvm_pass_manager: bool,
     // Instead of creating an object file by doing LLVM codegen, just
     // make the object file bitcode. Provides easy compatibility with
     // emscripten's ecc compiler, when used as the linker.
@@ -129,6 +130,7 @@ impl ModuleConfig {
             vectorize_slp: false,
             merge_functions: false,
             inline_threshold: None,
+            new_llvm_pass_manager: false,
         }
     }
 
@@ -137,6 +139,7 @@ impl ModuleConfig {
         self.no_prepopulate_passes = sess.opts.cg.no_prepopulate_passes;
         self.no_builtins = no_builtins || sess.target.target.options.no_builtins;
         self.inline_threshold = sess.opts.cg.inline_threshold;
+        self.new_llvm_pass_manager = sess.opts.debugging_opts.new_llvm_pass_manager;
         self.obj_is_bitcode =
             sess.target.target.options.obj_is_bitcode || sess.opts.cg.linker_plugin_lto.enabled();
         let embed_bitcode =

src/librustc_session/options.rs

@@ -948,4 +948,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
          (such as entering an empty infinite loop) by inserting llvm.sideeffect"),
     deduplicate_diagnostics: Option<bool> = (None, parse_opt_bool, [UNTRACKED],
         "deduplicate identical diagnostics"),
+    new_llvm_pass_manager: bool = (true, parse_bool, [TRACKED],
+        "use new LLVM pass manager"),
 }