[KnownBits] Add KnownBits::commonBits helper. NFCI.

We have a frequent pattern where we're merging two KnownBits to get the common/shared bits, and I just fell for the gotcha where I tried to use the & operator to merge them........

1 files changed, 5 insertions, 9 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 5ff4fcb..c86fa81 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1160,8 +1160,7 @@ static void computeKnownBitsFromOperator(const Operator *I,
     computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
 
     // Only known if known in both the LHS and RHS.
-    Known.One &= Known2.One;
-    Known.Zero &= Known2.Zero;
+    Known = KnownBits::commonBits(Known, Known2);
 
     if (SPF == SPF_ABS) {
       // RHS from matchSelectPattern returns the negation part of abs pattern.
@@ -1515,11 +1514,10 @@ static void computeKnownBitsFromOperator(const Operator *I,
         // Recurse, but cap the recursion to one level, because we don't
         // want to waste time spinning around in loops.
         computeKnownBits(IncValue, Known2, MaxAnalysisRecursionDepth - 1, RecQ);
-        Known.Zero &= Known2.Zero;
-        Known.One &= Known2.One;
+        Known = KnownBits::commonBits(Known, Known2);
         // If all bits have been ruled out, there's no need to check
         // more operands.
-        if (!Known.Zero && !Known.One)
+        if (Known.isUnknown())
           break;
       }
     }
@@ -1710,8 +1708,7 @@ static void computeKnownBitsFromOperator(const Operator *I,
     if (!!DemandedRHS) {
       const Value *RHS = Shuf->getOperand(1);
       computeKnownBits(RHS, DemandedRHS, Known2, Depth + 1, Q);
-      Known.One &= Known2.One;
-      Known.Zero &= Known2.Zero;
+      Known = KnownBits::commonBits(Known, Known2);
     }
     break;
   }
@@ -1740,8 +1737,7 @@ static void computeKnownBitsFromOperator(const Operator *I,
     DemandedVecElts.clearBit(EltIdx);
     if (!!DemandedVecElts) {
       computeKnownBits(Vec, DemandedVecElts, Known2, Depth + 1, Q);
-      Known.One &= Known2.One;
-      Known.Zero &= Known2.Zero;
+      Known = KnownBits::commonBits(Known, Known2);
     }
     break;
   }