Backport of #49904

src/librustc/hir/mod.rs

@@ -2280,6 +2280,7 @@ bitflags! {
         const NAKED                     = 0b0001_0000;
         const NO_MANGLE                 = 0b0010_0000;
         const RUSTC_STD_INTERNAL_SYMBOL = 0b0100_0000;
+        const NO_DEBUG                  = 0b1000_0000;
     }
 }
 

src/librustc_driver/lib.rs

@@ -24,6 +24,7 @@
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(set_stdio)]
+#![feature(no_debug)]
 
 extern crate arena;
 extern crate getopts;
@@ -230,6 +231,9 @@ fn load_backend_from_dylib(path: &Path) -> fn() -> Box<TransCrate> {
 
 pub fn get_trans(sess: &Session) -> Box<TransCrate> {
     static INIT: Once = ONCE_INIT;
+
+    #[allow(deprecated)]
+    #[no_debug]
     static mut LOAD: fn() -> Box<TransCrate> = || unreachable!();
 
     INIT.call_once(|| {

src/librustc_trans/debuginfo/metadata.rs

@@ -23,6 +23,7 @@ use llvm::{self, ValueRef};
 use llvm::debuginfo::{DIType, DIFile, DIScope, DIDescriptor,
                       DICompositeType, DILexicalBlock, DIFlags};
 
+use rustc::hir::TransFnAttrFlags;
 use rustc::hir::def::CtorKind;
 use rustc::hir::def_id::{DefId, CrateNum, LOCAL_CRATE};
 use rustc::ty::fold::TypeVisitor;
@@ -41,7 +42,7 @@ use std::ffi::CString;
 use std::fmt::Write;
 use std::ptr;
 use std::path::{Path, PathBuf};
-use syntax::{ast, attr};
+use syntax::ast;
 use syntax::symbol::{Interner, InternedString, Symbol};
 use syntax_pos::{self, Span, FileName};
 
@@ -1644,11 +1645,17 @@ pub fn create_global_var_metadata(cx: &CodegenCx,
     }
 
     let tcx = cx.tcx;
-    let no_mangle = attr::contains_name(&tcx.get_attrs(def_id), "no_mangle");
+    let attrs = tcx.trans_fn_attrs(def_id);
+
+    if attrs.flags.contains(TransFnAttrFlags::NO_DEBUG) {
+        return;
+    }
+
+    let no_mangle = attrs.flags.contains(TransFnAttrFlags::NO_MANGLE);
     // We may want to remove the namespace scope if we're in an extern block, see:
     // https://github.com/rust-lang/rust/pull/46457#issuecomment-351750952
     let var_scope = get_namespace_for_item(cx, def_id);
-    let span = cx.tcx.def_span(def_id);
+    let span = tcx.def_span(def_id);
 
     let (file_metadata, line_number) = if span != syntax_pos::DUMMY_SP {
         let loc = span_start(cx, span);

src/librustc_trans/debuginfo/mod.rs

@@ -23,14 +23,15 @@ use self::source_loc::InternalDebugLocation::{self, UnknownLocation};
 use llvm;
 use llvm::{ModuleRef, ContextRef, ValueRef};
 use llvm::debuginfo::{DIFile, DIType, DIScope, DIBuilderRef, DISubprogram, DIArray, DIFlags};
+use rustc::hir::TransFnAttrFlags;
 use rustc::hir::def_id::{DefId, CrateNum};
 use rustc::ty::subst::Substs;
 
 use abi::Abi;
 use common::CodegenCx;
 use builder::Builder;
 use monomorphize::Instance;
-use rustc::ty::{self, ParamEnv, Ty};
+use rustc::ty::{self, ParamEnv, Ty, InstanceDef};
 use rustc::mir;
 use rustc::session::config::{self, FullDebugInfo, LimitedDebugInfo, NoDebugInfo};
 use rustc::util::nodemap::{DefIdMap, FxHashMap, FxHashSet};
@@ -210,13 +211,12 @@ pub fn create_function_debug_context<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
         return FunctionDebugContext::DebugInfoDisabled;
     }
 
-    for attr in instance.def.attrs(cx.tcx).iter() {
-        if attr.check_name("no_debug") {
+    if let InstanceDef::Item(def_id) = instance.def {
+        if cx.tcx.trans_fn_attrs(def_id).flags.contains(TransFnAttrFlags::NO_DEBUG) {
             return FunctionDebugContext::FunctionWithoutDebugInfo;
         }
     }
 
-    let containing_scope = get_containing_scope(cx, instance);
     let span = mir.span;
 
     // This can be the case for functions inlined from another crate
@@ -226,6 +226,7 @@ pub fn create_function_debug_context<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
     }
 
     let def_id = instance.def_id();
+    let containing_scope = get_containing_scope(cx, instance);
     let loc = span_start(cx, span);
     let file_metadata = file_metadata(cx, &loc.file.name, def_id.krate);
 

src/librustc_typeck/collect.rs

@@ -1785,6 +1785,8 @@ fn trans_fn_attrs<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, id: DefId) -> TransFnAt
             trans_fn_attrs.flags |= TransFnAttrFlags::NO_MANGLE;
         } else if attr.check_name("rustc_std_internal_symbol") {
             trans_fn_attrs.flags |= TransFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
+        } else if attr.check_name("no_debug") {
+            trans_fn_attrs.flags |= TransFnAttrFlags::NO_DEBUG;
         } else if attr.check_name("inline") {
             trans_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
                 if attr.path != "inline" {