Add a test for #22892

src/test/ui/asm/invalid-inline-asm.rs

@@ -0,0 +1,9 @@
+#![feature(asm)]
+
+fn main() {
+    let byte = 0;
+    let port = 0x80;
+
+    unsafe { asm!("out %al, %dx" :: "a" (byte), "d" (port) :: "volatile"); }
+    //~^ ERROR couldn't allocate input reg for constraint 'a'
+}

src/test/ui/asm/invalid-inline-asm.stderr

@@ -0,0 +1,8 @@
+error: couldn't allocate input reg for constraint 'a'
+  --> $DIR/invalid-inline-asm.rs:7:14
+   |
+LL |     unsafe { asm!("out %al, %dx" :: "a" (byte), "d" (port) :: "volatile"); }
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+