[ValueTracking] Introduce a KnownBits struct to wrap the two APInts for computeKnownBits

This patch introduces a new KnownBits struct that wraps the two APInt used by computeKnownBits. This allows us to treat them as more of a unit.

Initially I've just altered the signatures of computeKnownBits and InstCombine's simplifyDemandedBits to pass a KnownBits reference instead of two separate APInt references. I'll do similar to the SelectionDAG version of computeKnownBits/simplifyDemandedBits as a separate patch.

I've added a constructor that allows initializing both APInts to the same bit width with a starting value of 0. This reduces the repeated pattern of initializing both APInts. Once place default constructed the APInts so I added a default constructor for those cases.

Going forward I would like to add more methods that will work on the pairs. For example trunc, zext, and sext occur on both APInts together in several places. We should probably add a clear method that can be used to clear both pieces. Maybe a method to check for conflicting information. A method to return (Zero|One) so we don't write it out everywhere. Maybe a method for (Zero|One).isAllOnesValue() to determine if all bits are known. I'm sure there are many other methods we can come up with.

Differential Revision: https://reviews.llvm.org/D32376

llvm-svn: 301432

1 files changed, 7 insertions, 7 deletions

diff --git a/llvm/lib/Analysis/Lint.cpp b/llvm/lib/Analysis/Lint.cpp
index 2ca46b1fe87..0f04af54cdc 100644
--- a/llvm/lib/Analysis/Lint.cpp
+++ b/llvm/lib/Analysis/Lint.cpp
@@ -70,6 +70,7 @@
 #include "llvm/Pass.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/KnownBits.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
@@ -534,10 +535,9 @@ static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
   VectorType *VecTy = dyn_cast<VectorType>(V->getType());
   if (!VecTy) {
     unsigned BitWidth = V->getType()->getIntegerBitWidth();
-    APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-    computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC,
-                     dyn_cast<Instruction>(V), DT);
-    return KnownZero.isAllOnesValue();
+    KnownBits Known(BitWidth);
+    computeKnownBits(V, Known, DL, 0, AC, dyn_cast<Instruction>(V), DT);
+    return Known.Zero.isAllOnesValue();
   }
 
   // Per-component check doesn't work with zeroinitializer
@@ -556,9 +556,9 @@ static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
     if (isa<UndefValue>(Elem))
       return true;
 
-    APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-    computeKnownBits(Elem, KnownZero, KnownOne, DL);
-    if (KnownZero.isAllOnesValue())
+    KnownBits Known(BitWidth);
+    computeKnownBits(Elem, Known, DL);
+    if (Known.Zero.isAllOnesValue())
       return true;
   }