various fixes for naked_asm! implementation

- fix for divergence
- fix error message
- fix another cranelift test
- fix some cranelift things
- don't set the NORETURN option for naked asm
- fix use of naked_asm! in doc comment
- fix use of naked_asm! in run-make test
- use `span_bug` in unreachable branch

example/mini_core.rs

@@ -726,6 +726,12 @@ fn index(&self, index: usize) -> &Self::Output {
     /* compiler built-in */
 }
 
+#[rustc_builtin_macro]
+#[rustc_macro_transparency = "semitransparent"]
+pub macro naked_asm() {
+    /* compiler built-in */
+}
+
 pub static A_STATIC: u8 = 42;
 
 #[lang = "panic_location"]

example/mini_core_hello_world.rs

@@ -390,7 +390,7 @@ fn stack_val_align() {
 #[naked]
 extern "C" fn naked_test() {
     unsafe {
-        asm!("ret", options(noreturn));
+        naked_asm!("ret");
     }
 }
 

src/base.rs

@@ -8,6 +8,7 @@
 use rustc_codegen_ssa::base::is_call_from_compiler_builtins_to_upstream_monomorphization;
 use rustc_index::IndexVec;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
+use rustc_middle::mir::InlineAsmMacro;
 use rustc_middle::ty::TypeVisitableExt;
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::layout::FnAbiOf;
@@ -57,6 +58,7 @@ pub(crate) fn codegen_fn<'tcx>(
 
         match &mir.basic_blocks[START_BLOCK].terminator().kind {
             TerminatorKind::InlineAsm {
+                asm_macro: InlineAsmMacro::NakedAsm,
                 template,
                 operands,
                 options,
@@ -498,6 +500,7 @@ fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
                 "tail calls are not yet supported in `rustc_codegen_cranelift` backend"
             ),
             TerminatorKind::InlineAsm {
+                asm_macro: _,
                 template,
                 operands,
                 options,