1 files changed, 92 insertions, 0 deletions
diff --git a/js/src/jit-test/tests/warp/string-substring-startswith-constant-string.js b/js/src/jit-test/tests/warp/string-substring-startswith-constant-string.js
new file mode 100644
index 0000000000..74ecef570d
--- /dev/null
+++ b/js/src/jit-test/tests/warp/string-substring-startswith-constant-string.js
@@ -0,0 +1,92 @@
+// Test case to cover String.prototype.substring as startsWith with a constant search string.
+//
+// String.prototype.substring comparison with a short (≤32 characters) constant string is
+// optimised during lowering.
+
+function* characters(...ranges) {
+  for (let [start, end] of ranges) {
+    for (let i = start; i <= end; ++i) {
+      yield i;
+    }
+  }
+}
+
+const ascii = [...characters(
+  [0x41, 0x5A], // A..Z
+  [0x61, 0x7A], // a..z
+  [0x30, 0x39], // 0..9
+)];
+
+const latin1 = [...characters(
+  [0xC0, 0xFF], // À..ÿ
+)];
+
+const twoByte = [...characters(
+  [0x100, 0x17E], // Ā..ž
+)];
+
+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 atomize(s) {
+  return Object.keys({[s]: 0})[0];
+}
+
+const operators = [
+  "==", "===", "!=", "!==",
+];
+
+for (let i = 1; i <= 32; ++i) {
+  let strings = [ascii, latin1, twoByte].flatMap(codePoints => [
+    // Same string as the input.
+    String.fromCodePoint(...codePoints.slice(0, i)),
+
+    // Same length as the input, but a different string.
+    String.fromCodePoint(...codePoints.slice(1, i + 1)),
+
+    // Shorter string than the input.
+    String.fromCodePoint(...codePoints.slice(0, i - 1)),
+
+    // Longer string than the input.
+    String.fromCodePoint(...codePoints.slice(0, i + 1)),
+  ]).flatMap(x => [
+    x,
+    toRope(x),
+    newString(x, {twoByte: true}),
+    atomize(x),
+  ]);
+
+  for (let codePoints of [ascii, latin1, twoByte]) {
+    let str = String.fromCodePoint(...codePoints.slice(0, i));
+
+    for (let op of operators) {
+      let fn = Function("strings", `
+        const expected = strings.map(x => {
+          // Prevent Warp compilation when computing the expected results.
+          with ({}) ;
+          return x.substring(0, ${str.length}) ${op} "${str}";
+        });
+
+        for (let i = 0; i < 250; ++i) {
+          let idx = i % strings.length;
+          let str = strings[idx];
+
+          let lhs = str.substring(0, ${str.length}) ${op} "${str}";
+          if (lhs !== expected[idx]) throw new Error();
+
+          let rhs = "${str}" ${op} str.substring(0, ${str.length});
+          if (rhs !== expected[idx]) throw new Error();
+        }
+      `);
+      fn(strings);
+    }
+  }
+}