[APInt] Add a simpler overload of multiplicativeInverse (#87610)

The current APInt::multiplicativeInverse takes a modulus which can be
any value, but all in-tree callers use a power of two. Moreover, most
callers want to use two to the power of the width of an existing APInt,
which is awkward because 2^N is not representable as an N-bit APInt.

Add a new overload of multiplicativeInverse which implicitly uses
2^BitWidth as the modulus.

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index d5ef63e..23f9ee2 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -3257,9 +3257,10 @@ TEST(APIntTest, MultiplicativeInverseExaustive) {
               .multiplicativeInverse(APInt::getSignedMinValue(BitWidth + 1))
               .trunc(BitWidth);
       APInt One = V * MulInv;
-      if (!V.isZero() && V.countr_zero() == 0) {
+      if (V[0]) {
         // Multiplicative inverse exists for all odd numbers.
         EXPECT_TRUE(One.isOne());
+        EXPECT_TRUE((V * V.multiplicativeInverse()).isOne());
       } else {
         // Multiplicative inverse does not exist for even numbers (and 0).
         EXPECT_TRUE(MulInv.isZero());