Forbid asm unwind to work with labels

compiler/rustc_builtin_macros/messages.ftl

@@ -19,6 +19,8 @@ builtin_macros_asm_expected_other = expected operand, {$is_global_asm ->
 
 builtin_macros_asm_explicit_register_name = explicit register arguments cannot have names
 
+builtin_macros_asm_mayunwind = asm labels are not allowed with the `may_unwind` option
+
 builtin_macros_asm_modifier_invalid = asm template modifier must be a single character
 
 builtin_macros_asm_mutually_exclusive = the `{$opt1}` and `{$opt2}` options are mutually exclusive

compiler/rustc_builtin_macros/src/asm.rs

@@ -245,6 +245,7 @@ pub fn parse_asm_args<'a>(
     let mut have_real_output = false;
     let mut outputs_sp = vec![];
     let mut regclass_outputs = vec![];
+    let mut labels_sp = vec![];
     for (op, op_sp) in &args.operands {
         match op {
             ast::InlineAsmOperand::Out { reg, expr, .. }
@@ -262,6 +263,9 @@ pub fn parse_asm_args<'a>(
                     regclass_outputs.push(*op_sp);
                 }
             }
+            ast::InlineAsmOperand::Label { .. } => {
+                labels_sp.push(*op_sp);
+            }
             _ => {}
         }
     }
@@ -273,6 +277,9 @@ pub fn parse_asm_args<'a>(
         // Bail out now since this is likely to confuse MIR
         return Err(err);
     }
+    if args.options.contains(ast::InlineAsmOptions::MAY_UNWIND) && !labels_sp.is_empty() {
+        dcx.emit_err(errors::AsmMayUnwind { labels_sp });
+    }
 
     if args.clobber_abis.len() > 0 {
         if is_global_asm {

compiler/rustc_builtin_macros/src/errors.rs

@@ -787,6 +787,13 @@ pub(crate) struct AsmNoReturn {
     pub(crate) outputs_sp: Vec<Span>,
 }
 
+#[derive(Diagnostic)]
+#[diag(builtin_macros_asm_mayunwind)]
+pub(crate) struct AsmMayUnwind {
+    #[primary_span]
+    pub(crate) labels_sp: Vec<Span>,
+}
+
 #[derive(Diagnostic)]
 #[diag(builtin_macros_global_asm_clobber_abi)]
 pub(crate) struct GlobalAsmClobberAbi {