Add a test for #28587

src/test/ui/asm/invalid-inline-asm-2.rs

@@ -0,0 +1,10 @@
+#![feature(asm)]
+
+fn main() {
+    let a: usize;
+
+    unsafe {
+        asm!("" : "=d"(a) : : : );
+        //~^ ERROR couldn't allocate output register for constraint 'd'
+    }
+}

src/test/ui/asm/invalid-inline-asm-2.stderr

@@ -0,0 +1,8 @@
+error: couldn't allocate output register for constraint 'd'
+  --> $DIR/invalid-inline-asm-2.rs:7:9
+   |
+LL |         asm!("" : "=d"(a) : : : );
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+