[NFC][KnownBits] Add getMinValue() / getMaxValue() methods

As it can be seen from accompanying cleanup, it is not unheard of
to write `~Known.Zero` meaning "what maximal value can this KnownBits
produce". But i think `~Known.Zero` isn't *that* self-explanatory,
as compared to a method with a name.

Note that not all `~Known.Zero` places were cleaned up,
only those where this arguably improves things.

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/unittests/Support/KnownBitsTest.cpp b/llvm/unittests/Support/KnownBitsTest.cpp
index c2b3b127cf1..372521dc5c9 100644
--- a/llvm/unittests/Support/KnownBitsTest.cpp
+++ b/llvm/unittests/Support/KnownBitsTest.cpp
@@ -127,4 +127,18 @@ TEST(KnownBitsTest, AddSubExhaustive) {
   TestAddSubExhaustive(false);
 }
 
+TEST(KnownBitsTest, GetMinMaxVal) {
+  unsigned Bits = 4;
+  ForeachKnownBits(Bits, [&](const KnownBits &Known) {
+    APInt Min = APInt::getMaxValue(Bits);
+    APInt Max = APInt::getMinValue(Bits);
+    ForeachNumInKnownBits(Known, [&](const APInt &N) {
+      Min = APIntOps::umin(Min, N);
+      Max = APIntOps::umax(Max, N);
+    });
+    EXPECT_EQ(Min, Known.getMinValue());
+    EXPECT_EQ(Max, Known.getMaxValue());
+  });
+}
+
 } // end anonymous namespace