error[E0661]: output operand constraint lacks '=' or '+'
  --> $DIR/E0661.rs:8:23
   |
LL |     llvm_asm!("nop" : "r"(a));
   |                       ^^^

error[E0282]: type annotations needed
  --> $DIR/E0661.rs:7:9
   |
LL |     let a;
   |         ^ consider giving `a` a type

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0282, E0661.
For more information about an error, try `rustc --explain E0282`.