Add tests for issues #82833 and #82859

Author: nikic

src/test/ui/issues/issue-82833-slice-miscompile.rs

@@ -0,0 +1,17 @@
+// run-pass
+// compile-flags: -Ccodegen-units=1 -Cinline-threshold=0 -Clink-dead-code -Copt-level=0 -Cdebuginfo=2
+// ignore-tidy-linelength
+
+// Make sure LLVM does not miscompile this.
+
+fn make_string(ch: char) -> String {
+    let mut bytes = [0u8; 4];
+    ch.encode_utf8(&mut bytes).into()
+}
+
+fn main() {
+    let ch = '😃';
+    dbg!(ch);
+    let string = make_string(ch);
+    dbg!(string);
+}

src/test/ui/issues/issue-82859-slice-miscompile.rs

@@ -0,0 +1,19 @@
+// run-pass
+// compile-flags: -Copt-level=0 -Cdebuginfo=2
+
+// Make sure LLVM does not miscompile this.
+
+fn indirect_get_slice() -> &'static [usize] {
+    &[]
+}
+
+#[inline(always)]
+fn get_slice() -> &'static [usize] {
+    let ret = indirect_get_slice();
+    ret
+}
+
+fn main() {
+    let output = get_slice().len();
+    assert_eq!(output, 0);
+}