Tune the `is_ascii` implementation used for short slices

1 files changed, 35 insertions, 0 deletions

diff --git a/tests/assembly/slice-is_ascii.rs b/tests/assembly/slice-is_ascii.rs
new file mode 100644
index 00000000000..b3e1fee15a7
--- /dev/null
+++ b/tests/assembly/slice-is_ascii.rs
@@ -0,0 +1,35 @@
+// revisions: WIN LIN
+// [WIN] only-windows
+// [LIN] only-linux
+// assembly-output: emit-asm
+// compile-flags: --crate-type=lib -O -C llvm-args=-x86-asm-syntax=intel
+// min-llvm-version: 14
+// only-x86_64
+// ignore-sgx
+// ignore-debug
+
+#![feature(str_internals)]
+
+// CHECK-LABEL: is_ascii_simple_demo:
+#[no_mangle]
+pub fn is_ascii_simple_demo(bytes: &[u8]) -> bool {
+    // Linux (System V): pointer is rdi; length is rsi
+    // Windows: pointer is rcx; length is rdx.
+
+    // CHECK-NOT: mov
+    // CHECK-NOT: test
+    // CHECK-NOT: cmp
+
+    // CHECK: .[[LOOPHEAD:.+]]:
+    // CHECK-NEXT: mov [[TEMP:.+]], [[LEN:rsi|rdx]]
+    // CHECK-NEXT: sub [[LEN]], 1
+    // CHECK-NEXT: jb .[[LOOPEXIT:.+]]
+    // CHECK-NEXT: cmp byte ptr [{{rdi|rcx}} + [[TEMP]] - 1], 0
+    // CHECK-NEXT: jns .[[LOOPHEAD]]
+
+    // CHECK-NEXT: .[[LOOPEXIT]]:
+    // CHECK-NEXT: test [[TEMP]], [[TEMP]]
+    // CHECK-NEXT: sete al
+    // CHECK-NEXT: ret
+    core::slice::is_ascii_simple(bytes)
+}