tests/assembly-llvm/some-non-zero-from-atomic-optimization.rs: New test

tests/assembly-llvm/some-non-zero-from-atomic-optimization.rs

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+//! Regression test for <https://github.com/rust-lang/rust/issues/60044>.
+
+//@ assembly-output: emit-asm
+//@ only-x86_64
+
+// We want to check that the None case is optimized away
+//@ compile-flags: -O
+
+// Simplify the generated assembly
+//@ compile-flags: -Cforce-unwind-tables=no
+
+#![crate_type = "lib"]
+
+use std::num::NonZeroUsize;
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering::Relaxed;
+
+pub static X: AtomicUsize = AtomicUsize::new(1);
+
+/// This function function shall look like this:
+/// ```
+/// some_non_zero_from_atomic_get:
+///         movq    _RNvCs7C4TuIcXqwO_25some_non_zero_from_atomic1X@GOTPCREL(%rip), %rax
+///         movq    (%rax), %rax
+///         retq
+/// ```
+// CHECK-LABEL: some_non_zero_from_atomic_get:
+// CHECK-NEXT: movq    {{[_a-zA-Z0-9]+}}@GOTPCREL(%rip), %rax
+// CHECK-NEXT: movq    (%rax), %rax
+// CHECK-NEXT: retq
+#[no_mangle]
+pub unsafe fn some_non_zero_from_atomic_get() -> Option<NonZeroUsize> {
+    let x = X.load(Relaxed);
+    Some(NonZeroUsize::new_unchecked(x))
+}
+
+/// This function shall be identical to the above, which means:
+// CHECK-DAG: some_non_zero_from_atomic_get2 = some_non_zero_from_atomic_get
+#[no_mangle]
+pub unsafe fn some_non_zero_from_atomic_get2() -> usize {
+    match some_non_zero_from_atomic_get() {
+        Some(x) => x.get(),
+        None => unreachable!(), // shall be optimized out
+    }
+}