1 files changed, 115 insertions, 0 deletions
diff --git a/js/src/jit-test/tests/cacheir/string-at.js b/js/src/jit-test/tests/cacheir/string-at.js
new file mode 100644
index 0000000000..8dfb2f779e
--- /dev/null
+++ b/js/src/jit-test/tests/cacheir/string-at.js
@@ -0,0 +1,115 @@
+// Test String.prototype.at with negative and non-negative indices.
+
+function* characters(...ranges) {
+  for (let [start, end] of ranges) {
+    for (let i = start; i <= end; ++i) {
+      yield i;
+    }
+  }
+}
+
+const empty = [];
+
+const ascii = [...characters(
+  [0x41, 0x5A], // A..Z
+  [0x61, 0x7A], // a..z
+)];
+
+const latin1 = [...characters(
+  [0xC0, 0xFF], // À..ÿ
+)];
+
+const twoByte = [...characters(
+  [0x100, 0x17E], // Ā..ž
+)];
+
+function atomize(s) {
+  return Object.keys({[s]: 0})[0];
+}
+
+function codePoints() {
+  return [empty, ascii, latin1, twoByte];
+}
+
+function toRope(s) {
+  // Ropes have at least two characters.
+  if (s.length < 2) {
+    return s;
+  }
+  if (s.length === 2) {
+    return newRope(s[0], s[1]);
+  }
+  return newRope(s[0], s.substring(1));
+}
+
+function makeStrings() {
+  let strings = codePoints()
+  .map(codePoints => String.fromCodePoint(...codePoints))
+  .flatMap(x => [
+    x,
+    toRope(x),
+    newString(x, {twoByte: true}),
+    atomize(x),
+  ]);
+  return strings;
+}
+
+function testNonNegativeIndexConstant() {
+  let strings = makeStrings();
+  for (let i = 0; i < 200; ++i) {
+    let str = strings[i % strings.length];
+    let index = 0;
+    let ch = str.at(index);
+    let expected = str.charAt(index);
+    if (expected === "") expected = undefined;
+    assertEq(ch, expected);
+  }
+}
+for (let i = 0; i < 2; ++i) {
+  testNonNegativeIndexConstant();
+}
+
+function testNonNegativeIndex() {
+  let strings = makeStrings();
+  for (let i = 0; i < 200; ++i) {
+    let str = strings[i % strings.length];
+    let index = i & 3;
+    let ch = str.at(index);
+    let expected = str.charAt(index);
+    if (expected === "") expected = undefined;
+    assertEq(ch, expected);
+  }
+}
+for (let i = 0; i < 2; ++i) {
+  testNonNegativeIndex();
+}
+
+function testNegativeIndexConstant() {
+  let strings = makeStrings();
+  for (let i = 0; i < 200; ++i) {
+    let str = strings[i % strings.length];
+    let index = -1;
+    let ch = str.at(index);
+    let expected = str.charAt(str.length + index);
+    if (expected === "") expected = undefined;
+    assertEq(ch, expected);
+  }
+}
+for (let i = 0; i < 2; ++i) {
+  testNegativeIndexConstant();
+}
+
+function testNegativeIndex() {
+  let strings = makeStrings();
+  for (let i = 0; i < 200; ++i) {
+    let str = strings[i % strings.length];
+    let index = -(i & 3) - 1;
+    let ch = str.at(index);
+    let expected = str.charAt(str.length + index);
+    if (expected === "") expected = undefined;
+    assertEq(ch, expected);
+  }
+}
+for (let i = 0; i < 2; ++i) {
+  testNegativeIndex();
+}