[MLIR][Presburger] SlowMPInt::gcd: fix crash when sizes differ

[Groverkss]

LGTM.

mlir/lib/Analysis/Presburger/SlowMPInt.cpp

 /// is always non-negative.
 SlowMPInt detail::mod(const SlowMPInt &lhs, const SlowMPInt &rhs) {
   assert(rhs >= 1 && "mod is only supported for positive divisors!");
   return lhs % rhs < 0 ? lhs % rhs + rhs : lhs % rhs;
 }
 
 SlowMPInt detail::gcd(const SlowMPInt &a, const SlowMPInt &b) {
   assert(a >= 0 && b >= 0 && "operands must be non-negative!");
-  return SlowMPInt(llvm::APIntOps::GreatestCommonDivisor(a.val, b.val));
+  unsigned width = getMaxWidth(a.val, b.val);
+  return SlowMPInt(llvm::APIntOps::GreatestCommonDivisor(a.val.sext(width),
+                                                         b.val.sext(width)));
 }
 
 /// Returns the least common multiple of 'a' and 'b'.
 SlowMPInt detail::lcm(const SlowMPInt &a, const SlowMPInt &b) {
   SlowMPInt x = abs(a);
   SlowMPInt y = abs(b);
   return (x * y) / gcd(x, y);
 }

mlir/unittests/Analysis/Presburger/MPIntTest.cpp

for (const TypeParam &y : {x, x * x}) {
 
     EXPECT_EQ(mod(3 * y, y), 0);
     EXPECT_EQ(mod(3 * y + 1, y), 1);
     EXPECT_EQ(mod(3 * y + 2, y), 2);
 
     EXPECT_EQ(abs(y), y);
     EXPECT_EQ(abs(-y), y);
 
+    EXPECT_EQ(gcd(3 * y, three), three);
+    EXPECT_EQ(lcm(y, three), 3 * y);
     EXPECT_EQ(gcd(2 * y, 3 * y), y);
     EXPECT_EQ(lcm(2 * y, 3 * y), 6 * y);
     EXPECT_EQ(gcd(15 * y, 6 * y), 3 * y);
     EXPECT_EQ(lcm(15 * y, 6 * y), 30 * y);
   }
 }