[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, 4 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 357c303af08..d3002c5fb75 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -45,6 +45,7 @@
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/KnownBits.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;
@@ -1038,9 +1039,9 @@ unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
          "getOrEnforceKnownAlignment expects a pointer!");
   unsigned BitWidth = DL.getPointerTypeSizeInBits(V->getType());
 
-  APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-  computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC, CxtI, DT);
-  unsigned TrailZ = KnownZero.countTrailingOnes();
+  KnownBits Known(BitWidth);
+  computeKnownBits(V, Known, DL, 0, AC, CxtI, DT);
+  unsigned TrailZ = Known.Zero.countTrailingOnes();
 
   // Avoid trouble with ridiculously large TrailZ values, such as
   // those computed from a null pointer.