transpile: switch __builtin_arm_yield to the more direct, unstable equivalent of __yield

Author: kkysen

c2rust-transpile/src/translator/builtins.rs

@@ -380,14 +380,9 @@ impl<'c> Translation<'c> {
                 })
             }
 
-            "__builtin_ia32_pause" | "__builtin_arm_yield" => {
+            "__builtin_ia32_pause" => {
                 // `spin_loop()` is implemented as `_mm_pause()` (the `pause` instruction) on `x86`/`x86_64`,
                 // but it's the safe and cross-platform version of it, so prefer it.
-                // On `arm`, it's implemented as `yield`, although on `aarch64`,
-                // it's implemented as `isb` instead as this is more efficient.
-                // See <https://github.com/rust-lang/rust/commit/c064b6560b7ce0adeb9bbf5d7dcf12b1acb0c807>.
-                // `core::arch::aarch64::__yield()` could be used instead,
-                // but it's unstable (`#![feature(stdarch_arm_hints)]`), so it's not ideal.
                 let spin_loop = mk().abs_path_expr(vec!["core", "hint", "spin_loop"]);
                 let call = mk().call_expr(spin_loop, vec![]);
                 self.convert_side_effects_expr(
@@ -397,6 +392,18 @@ impl<'c> Translation<'c> {
                 )
             }
 
+            "__builtin_arm_yield" => {
+                let fn_name = "__yield";
+                self.import_simd_function(fn_name)?;
+                let ident = mk().ident_expr(fn_name);
+                let call = mk().call_expr(ident, vec![]);
+                self.convert_side_effects_expr(
+                    ctx,
+                    WithStmts::new_val(call),
+                    "Builtin is not supposed to be used",
+                )
+            }
+
             // SIMD builtins:
             "__builtin_ia32_aeskeygenassist128" => {
                 self.convert_simd_builtin(ctx, "_mm_aeskeygenassist_si128", args)