compiler: compare and hash ExternAbi like its string

Directly map each ExternAbi variant to its string and back again.
This has a few advantages:
- By making the ABIs compare equal to their strings, we can easily
  lexicographically sort them and use that sorted slice at runtime.
- We no longer need a workaround to make sure the hashes remain stable,
  as they already naturally are (by being the hashes of unique strings).
- The compiler can carry around less &str wide pointers

1 files changed, 8 insertions, 0 deletions

diff --git a/compiler/rustc_abi/src/extern_abi/tests.rs b/compiler/rustc_abi/src/extern_abi/tests.rs
index 72c0f183d50..44ea58d47c2 100644
--- a/compiler/rustc_abi/src/extern_abi/tests.rs
+++ b/compiler/rustc_abi/src/extern_abi/tests.rs
@@ -27,3 +27,11 @@ fn indices_are_correct() {
         assert_eq!(i, abi_data.abi.index());
     }
 }
+
+#[test]
+fn guarantee_lexicographic_ordering() {
+    let abis = ExternAbi::ALL_VARIANTS;
+    let mut sorted_abis = abis.to_vec();
+    sorted_abis.sort_unstable();
+    assert_eq!(abis, sorted_abis);
+}