Require integer views to stay below 2^53 exactly, and fix corpus 1420

packages/compiler/src/backend/llvm/integer-values.ts

@@ -65,6 +65,22 @@ function magnitude(range: IntegerRange): number {
   return Math.max(Math.abs(range.min), Math.abs(range.max));
 }
 
+/** The bounds of a sum and a product of two magnitude bounds, as doubles.
+ * Below 2^53 the double result is the integer; above it the result is past
+ * every exactness limit either way, and rounding moves it far less than the
+ * margin from WIDE_BOUND to the i64 range. A result of exactly 2^53 may
+ * stand for 2^53 + 1 (2^53 - 1 + 2 rounds to 2^53), so it moves to the next
+ * double up unless the sum is exactly 2^53. */
+function sumBound(a: number, b: number): number {
+  const sum = a + b;
+  return sum === EXACT_DOUBLES && EXACT_DOUBLES - a !== b ? sum + 2 : sum;
+}
+
+function productBound(a: number, b: number): number {
+  const product = a * b;
+  return product === EXACT_DOUBLES ? product + 2 : product;
+}
+
 /** The wide view of `l op r` for `+`, `-` and `*` when the exact operands
  * have no proven result range (their product or sum may pass 2^53).
  *
@@ -98,14 +114,14 @@ export function wideArithmetic(
   if (op === "*") {
     if (lv.below !== Infinity || rv.below !== Infinity) return null;
     below = EXACT_DOUBLES;
-    bound = lv.bound * rv.bound;
+    bound = productBound(lv.bound, rv.bound);
   } else if (lv.below === Infinity && rv.below === Infinity) {
     below = EXACT_DOUBLES;
-    bound = lv.bound + rv.bound;
+    bound = sumBound(lv.bound, rv.bound);
   } else if (lv.below === Infinity || rv.below === Infinity) {
     const [exact, wide] = lv.below === Infinity ? [lv, rv] : [rv, lv];
     below = Math.min(wide.below - exact.bound, EXACT_DOUBLES);
-    bound = exact.bound + wide.bound;
+    bound = sumBound(exact.bound, wide.bound);
   } else return null;
   if (!(bound <= WIDE_BOUND) || below < INDEX_LIMIT) return null;
   const operand = (value: LlValue, integer: LlInteger | null): string =>

tests/corpus/7982-integer-view-compares.ts

@@ -60,6 +60,20 @@ function nearLimit(start: number): string {
   return seen.join(" ");
 }
 
+function atLimit(start: number, end: number): string {
+  // A counter of integer locals only, up to 2^53 - 1: `i + 2` may be
+  // 2^53 + 1, whose double is 2^53, so `i + 1 === i + 2` holds at the end.
+  let same = 0;
+  let above = 0;
+  let mixed = 0;
+  for (let i = start; i <= end; i++) {
+    if (i + 1 === i + 2) same++;
+    if (i + 2 > 9007199254740992) above++;
+    mixed += (i * 2) % 3;
+  }
+  return `${same} ${above} ${mixed}`;
+}
+
 console.log(heapSort(new Int32Array([5, -3, 9, 0, 9, 2147483647, -2147483648, 7, 1])));
 console.log(heapSort(new Int32Array([])), heapSort(new Int32Array([4])));
 console.log(neighbors(new Float64Array([1, 2, 3, 4])));
@@ -67,3 +81,5 @@ const sorted = new Int32Array([-5, -1, 0, 0, 3, 8, 8, 13]);
 console.log([-6, -1, 0, 1, 8, 13, 14].map((v) => lowerBound(sorted, v)).join());
 console.log(nearLimit(9007199254740988));
 console.log(nearLimit(-9007199254740991));
+console.log(atLimit(9007199254740988, 9007199254740991));
+console.log(atLimit(-9007199254740991, -9007199254740988));