Rollup merge of #47618 - mrhota:dw_at_noreturn, r=michaelwoerister

Teach rustc about DW_AT_noreturn and a few more DIFlags

We achieve two small things with this PR:
1. We provide definitions for a few additional llvm debuginfo flags
1. We _use_ one of these new flags, `FlagNoReturn`, and add it to debuginfo for functions with the never return type (`!`).

src/librustc_llvm/ffi.rs

@@ -498,6 +498,10 @@ pub mod debuginfo {
             const FlagStaticMember        = (1 << 12);
             const FlagLValueReference     = (1 << 13);
             const FlagRValueReference     = (1 << 14);
+            const FlagExternalTypeRef     = (1 << 15);
+            const FlagIntroducedVirtual   = (1 << 18);
+            const FlagBitField            = (1 << 19);
+            const FlagNoReturn            = (1 << 20);
             const FlagMainSubprogram      = (1 << 21);
         }
     }

src/librustc_trans/debuginfo/mod.rs

@@ -270,6 +270,9 @@ pub fn create_function_debug_context<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
         }
         None => {}
     };
+    if sig.output().is_never() {
+        flags = flags | DIFlags::FlagNoReturn;
+    }
 
     let fn_metadata = unsafe {
         llvm::LLVMRustDIBuilderCreateFunction(

src/rustllvm/RustWrapper.cpp

@@ -457,9 +457,13 @@ enum class LLVMRustDIFlags : uint32_t {
   FlagStaticMember = (1 << 12),
   FlagLValueReference = (1 << 13),
   FlagRValueReference = (1 << 14),
-  FlagMainSubprogram      = (1 << 21),
+  FlagExternalTypeRef = (1 << 15),
+  FlagIntroducedVirtual = (1 << 18),
+  FlagBitField = (1 << 19),
+  FlagNoReturn = (1 << 20),
+  FlagMainSubprogram = (1 << 21),
   // Do not add values that are not supported by the minimum LLVM
-  // version we support!
+  // version we support! see llvm/include/llvm/IR/DebugInfoFlags.def
 };
 
 inline LLVMRustDIFlags operator&(LLVMRustDIFlags A, LLVMRustDIFlags B) {
@@ -544,7 +548,19 @@ static unsigned fromRust(LLVMRustDIFlags Flags) {
   if (isSet(Flags & LLVMRustDIFlags::FlagRValueReference)) {
     Result |= DINode::DIFlags::FlagRValueReference;
   }
+  if (isSet(Flags & LLVMRustDIFlags::FlagExternalTypeRef)) {
+    Result |= DINode::DIFlags::FlagExternalTypeRef;
+  }
+  if (isSet(Flags & LLVMRustDIFlags::FlagIntroducedVirtual)) {
+    Result |= DINode::DIFlags::FlagIntroducedVirtual;
+  }
+  if (isSet(Flags & LLVMRustDIFlags::FlagBitField)) {
+    Result |= DINode::DIFlags::FlagBitField;
+  }
 #if LLVM_RUSTLLVM || LLVM_VERSION_GE(4, 0)
+  if (isSet(Flags & LLVMRustDIFlags::FlagNoReturn)) {
+    Result |= DINode::DIFlags::FlagNoReturn;
+  }
   if (isSet(Flags & LLVMRustDIFlags::FlagMainSubprogram)) {
     Result |= DINode::DIFlags::FlagMainSubprogram;
   }

src/test/codegen/noreturnflag.rs

@@ -0,0 +1,24 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-tidy-linelength
+// min-llvm-version 4.0
+
+// compile-flags: -g -C no-prepopulate-passes
+
+// CHECK: {{.*}}DISubprogram{{.*}}name: "foo"{{.*}}DIFlagNoReturn
+
+fn foo() -> ! {
+    loop {}
+}
+
+pub fn main() {
+    foo();
+}