1 files changed, 59 insertions, 0 deletions
diff --git a/js/src/jit-test/tests/jaeger/loops/multiply-by-int32min.js b/js/src/jit-test/tests/jaeger/loops/multiply-by-int32min.js
new file mode 100644
index 0000000000..bc692f1480
--- /dev/null
+++ b/js/src/jit-test/tests/jaeger/loops/multiply-by-int32min.js
@@ -0,0 +1,59 @@
+function foo()
+{
+  // Range analysis incorrectly computes a range for the multiplication.  Once
+  // that incorrect range is computed, the goal is to compute a new value whose
+  // range analysis *thinks* is in int32_t range, but which goes past it using
+  // JS semantics.
+  //
+  // On the final iteration, in JS semantics, the multiplication produces 0, and
+  // the next addition 0x7fffffff.  Adding any positive integer to that goes
+  // past int32_t range: here, (0x7fffffff + 5) or 2147483652.
+  //
+  // Range analysis instead thinks the multiplication produces a value in the
+  // range [INT32_MIN, INT32_MIN], and the next addition a value in the range
+  // [-1, -1].  Adding any positive value to that doesn't overflow int32_t range
+  // but *does* overflow the actual range in JS semantics.  Thus omitting
+  // overflow checks produces the value 0x80000004, which interpreting as signed
+  // is (INT32_MIN + 4) or -2147483644.
+  //
+  // For this test to trigger the bug it was supposed to trigger:
+  //
+  //   * 0x7fffffff must be the LHS, not RHS, of the addition in the loop, and
+  //   * i must not be incremented using ++
+  //
+  // The first is required because JM LoopState doesn't treat *both* V + mul and
+  // mul + V as not overflowing, when V is known to be int32_t -- only V + mul.
+  // (JM pessimally assumes V's type might change before it's evaluated.  This
+  // obviously can't happen if V is a constant, but JM's puny little mind
+  // doesn't detect this possibility now.)
+  //
+  // The second is required because JM LoopState only ignores integer overflow
+  // on multiplications if the enclosing loop is a "constrainedLoop" (the name
+  // of the relevant field).  Loops become unconstrained when unhandled ops are
+  // found in the loop.  Increment operators generate a DUP op, which is not
+  // presently a handled op, causing the loop to become unconstrained.
+  for (var i = 0; i < 15; i = i + 1) {
+    var y = (0x7fffffff + ((i & 1) * -2147483648)) + 5;
+  }
+  return y;
+}
+assertEq(foo(), (0x7fffffff + ((14 & 1) * -2147483648)) + 5);
+
+function bar()
+{
+  // Variation on the theme of the above test with -1 as the other half of the
+  // INT32_MIN multiplication, which *should* result in -INT32_MIN on multiply
+  // (exceeding int32_t range).
+  //
+  // Here, range analysis again thinks the range of the multiplication is
+  // INT32_MIN.  We'd overflow-check except that adding zero (on the LHS, see
+  // above) prevents overflow checking, so range analysis thinks the range is
+  // [INT32_MIN, INT32_MIN] when -INT32_MIN is actually possible.  This direct
+  // result of the multiplication is already out of int32_t range, so no need to
+  // add anything to bias it outside int32_t range to get a wrong result.
+  for (var i = 0; i < 17; i = i + 1) {
+    var y = (0 + ((-1 + (i & 1)) * -2147483648));
+  }
+  return y;
+}
+assertEq(bar(), (0 + ((-1 + (16 & 1)) * -2147483648)));