[KnownBits] Improve `KnownBits::udiv`

We can more precisely determine the upper bits doing `MaxNum /
MinDenum` as opposed to only using the MSB.

As well, if the `exact` flag is set, we can sometimes determine some
of the low-bits.

Differential Revision: https://reviews.llvm.org/D150094

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/unittests/Support/KnownBitsTest.cpp b/llvm/unittests/Support/KnownBitsTest.cpp
index 22dcbed..0322da6 100644
--- a/llvm/unittests/Support/KnownBitsTest.cpp
+++ b/llvm/unittests/Support/KnownBitsTest.cpp
@@ -251,6 +251,16 @@ TEST(KnownBitsTest, BinaryExhaustive) {
       checkCorrectnessOnlyBinary);
   testBinaryOpExhaustive(
       [](const KnownBits &Known1, const KnownBits &Known2) {
+        return KnownBits::udiv(Known1, Known2, /*Exact*/ true);
+      },
+      [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
+        if (N2.isZero() || !N1.urem(N2).isZero())
+          return std::nullopt;
+        return N1.udiv(N2);
+      },
+      checkCorrectnessOnlyBinary);
+  testBinaryOpExhaustive(
+      [](const KnownBits &Known1, const KnownBits &Known2) {
         return KnownBits::sdiv(Known1, Known2);
       },
       [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {