add inline attribute and codegen test

Author: edwloef

library/core/src/slice/rotate.rs

@@ -10,6 +10,7 @@ type BufType = [usize; 32];
 /// # Safety
 ///
 /// The specified range must be valid for reading and writing.
+#[inline]
 pub(super) unsafe fn ptr_rotate<T>(left: usize, mid: *mut T, right: usize) {
     if T::IS_ZST {
         return;

tests/codegen/lib-optimizations/slice_rotate.rs

@@ -0,0 +1,74 @@
+//@ compile-flags: -O -Cllvm-args=--inline-threshold=346
+
+#![crate_type = "lib"]
+
+// Ensure that the simple case of rotating by a constant 1 optimizes to the obvious thing
+
+// CHECK-LABEL: @rotate_left_by_one
+#[no_mangle]
+pub fn rotate_left_by_one(slice: &mut [i32]) {
+    // CHECK-NOT: phi
+    // CHECK-NOT: call
+    // CHECK-NOT: load
+    // CHECK-NOT: store
+    // CHECK-NOT: getelementptr
+    // CHECK: %[[END:.+]].i = getelementptr inbounds i8, ptr %slice.0
+    // CHECK-NEXT: %dim.i.i.i = getelementptr inbounds i32, ptr %slice.0
+    // CHECK-NEXT: %[[LAST:.+]] = load i32, ptr %slice.0
+    // CHECK-NEXT: %[[FIRST:.+]] = shl i64 %k.i, 2
+    // CHECK-NEXT: call void @llvm.memmove
+    // CHECK-NEXT: store i32 %[[LAST]], ptr %dim.i.i
+    // CHECK-NOT: phi
+    // CHECK-NOT: call
+    // CHECK-NOT: load
+    // CHECK-NOT: store
+    // CHECK-NOT: getelementptr
+    // CHECK: ret void
+    if !slice.is_empty() {
+        slice.rotate_left(1);
+    }
+}
+
+// CHECK-LABEL: @rotate_right_by_one
+#[no_mangle]
+pub fn rotate_right_by_one(slice: &mut [i32]) {
+    // CHECK-NOT: phi
+    // CHECK-NOT: call
+    // CHECK-NOT: load
+    // CHECK-NOT: store
+    // CHECK-NOT: getelementptr
+    // CHECK: %[[END:.+]].i = getelementptr inbounds i32, ptr %slice.0
+    // CHECK-NOT: phi
+    // CHECK-NOT: call
+    // CHECK-NOT: load
+    // CHECK-NOT: store
+    // CHECK-NOT: getelementptr
+    // CHECK: %dim.i.i.i = getelementptr inbounds i8, ptr %slice.0
+    // CHECK-NOT: phi
+    // CHECK-NOT: call
+    // CHECK-NOT: load
+    // CHECK-NOT: store
+    // CHECK-NOT: getelementptr
+    // CHECK: %[[TWO_LAST:.+]] = load i32, ptr %slice.0
+    // CHECK-NEXT: %[[TWO_FIRST:.+]] = load i32, ptr %[[END]].i
+    // CHECK-NEXT: store i32 %[[TWO_FIRST]], ptr %slice.0
+    // CHECK-NEXT: store i32 %[[TWO_LAST]], ptr %dim.i.i
+    // CHECK-NOT: phi
+    // CHECK-NOT: call
+    // CHECK-NOT: load
+    // CHECK-NOT: store
+    // CHECK-NOT: getelementptr
+    // CHECK: %[[FIRST:.+]] = load i32, ptr %[[END]].i
+    // CHECK-NEXT: %[[LAST:.+]] = shl i64 %mid.i, 2
+    // CHECK-NEXT: call void @llvm.memmove
+    // CHECK-NEXT: store i32 %[[FIRST]], ptr %slice.0
+    // CHECK-NOT: phi
+    // CHECK-NOT: call
+    // CHECK-NOT: load
+    // CHECK-NOT: store
+    // CHECK-NOT: getelementptr
+    // CHECK: ret void
+    if !slice.is_empty() {
+        slice.rotate_right(1);
+    }
+}