Auto merge of #50304 - nox:uninhabited-output, r=eddyb

Mark functions returning uninhabited types as noreturn

Author: bors

src/librustc_trans/debuginfo/mod.rs

@@ -271,7 +271,7 @@ pub fn create_function_debug_context<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
         }
         None => {}
     };
-    if sig.output().is_never() {
+    if cx.layout_of(sig.output()).abi == ty::layout::Abi::Uninhabited {
         flags = flags | DIFlags::FlagNoReturn;
     }
 

src/librustc_trans/declare.rs

@@ -23,6 +23,7 @@
 use llvm::{self, ValueRef};
 use llvm::AttributePlace::Function;
 use rustc::ty::{self, Ty};
+use rustc::ty::layout::{self, LayoutOf};
 use rustc::session::config::Sanitizer;
 use rustc_target::spec::PanicStrategy;
 use abi::{Abi, FnType, FnTypeExt};
@@ -133,8 +134,7 @@ pub fn declare_fn<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, name: &str,
     let fty = FnType::new(cx, sig, &[]);
     let llfn = declare_raw_fn(cx, name, fty.llvm_cconv(), fty.llvm_type(cx));
 
-    // FIXME(canndrew): This is_never should really be an is_uninhabited
-    if sig.output().is_never() {
+    if cx.layout_of(sig.output()).abi == layout::Abi::Uninhabited {
         llvm::Attribute::NoReturn.apply_llfn(Function, llfn);
     }
 

src/test/codegen/noreturnflag.rs

@@ -8,17 +8,27 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// compile-flags: -g -C no-prepopulate-passes
 // ignore-tidy-linelength
 // min-llvm-version 4.0
 
-// compile-flags: -g -C no-prepopulate-passes
-
-// CHECK: {{.*}}DISubprogram{{.*}}name: "foo"{{.*}}DIFlagNoReturn
+#![crate_type = "lib"]
 
-fn foo() -> ! {
+#[no_mangle]
+pub fn foo() -> ! {
+// CHECK: @foo() unnamed_addr #0
     loop {}
 }
 
-pub fn main() {
-    foo();
+pub enum EmptyEnum {}
+
+#[no_mangle]
+pub fn bar() -> EmptyEnum {
+// CHECK: @bar() unnamed_addr #0
+    loop {}
 }
+
+// CHECK: attributes #0 = {{{.*}} noreturn {{.*}}}
+
+// CHECK: DISubprogram(name: "foo", {{.*}} DIFlagNoReturn
+// CHECK: DISubprogram(name: "bar", {{.*}} DIFlagNoReturn