[KnownBits] Make `{s,u}{add,sub}_sat` optimal (#113096)

Changes are:
    1) Make signed-overflow detection optimal
    2) For signed-overflow, try to rule out direction even if we can't
       totally rule out overflow.
    3) Intersect add/sub assuming no overflow with possible overflow
       clamping values as opposed to add/sub without the assumption.

1 files changed, 4 insertions, 8 deletions

diff --git a/llvm/unittests/Support/KnownBitsTest.cpp b/llvm/unittests/Support/KnownBitsTest.cpp
index b16368d..ce0bf86 100644
--- a/llvm/unittests/Support/KnownBitsTest.cpp
+++ b/llvm/unittests/Support/KnownBitsTest.cpp
@@ -383,26 +383,22 @@ TEST(KnownBitsTest, BinaryExhaustive) {
       "sadd_sat", KnownBits::sadd_sat,
       [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
         return N1.sadd_sat(N2);
-      },
-      /*CheckOptimality=*/false);
+      });
   testBinaryOpExhaustive(
       "uadd_sat", KnownBits::uadd_sat,
       [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
         return N1.uadd_sat(N2);
-      },
-      /*CheckOptimality=*/false);
+      });
   testBinaryOpExhaustive(
       "ssub_sat", KnownBits::ssub_sat,
       [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
         return N1.ssub_sat(N2);
-      },
-      /*CheckOptimality=*/false);
+      });
   testBinaryOpExhaustive(
       "usub_sat", KnownBits::usub_sat,
       [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
         return N1.usub_sat(N2);
-      },
-      /*CheckOptimality=*/false);
+      });
   testBinaryOpExhaustive(
       "shl",
       [](const KnownBits &Known1, const KnownBits &Known2) {