src/test/mir-opt/dest-prop/copy_propagation_arg.rs

   1 // Check that DestinationPropagation does not propagate an assignment to a function argument
   2 // (doing so can break usages of the original argument value)
   3 // compile-flags: -Zunsound-mir-opts
   4 fn dummy(x: u8) -> u8 {
   5     x
   6 }
   7
   8 // EMIT_MIR copy_propagation_arg.foo.DestinationPropagation.diff
   9 fn foo(mut x: u8) {
  10     // calling `dummy` to make an use of `x` that copyprop cannot eliminate
  11     x = dummy(x); // this will assign a local to `x`
  12 }
  13
  14 // EMIT_MIR copy_propagation_arg.bar.DestinationPropagation.diff
  15 fn bar(mut x: u8) {
  16     dummy(x);
  17     x = 5;
  18 }
  19
  20 // EMIT_MIR copy_propagation_arg.baz.DestinationPropagation.diff
  21 fn baz(mut x: i32) {
  22     // self-assignment to a function argument should be eliminated
  23     x = x;
  24 }
  25
  26 // EMIT_MIR copy_propagation_arg.arg_src.DestinationPropagation.diff
  27 fn arg_src(mut x: i32) -> i32 {
  28     let y = x;
  29     x = 123; // Don't propagate this assignment to `y`
  30     y
  31 }
  32
  33 fn main() {
  34     // Make sure the function actually gets instantiated.
  35     foo(0);
  36     bar(0);
  37     baz(0);
  38     arg_src(0);
  39 }