[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/Scalar/GuardWidening.cpp b/llvm/lib/Transforms/Scalar/GuardWidening.cpp
index 7019287954a..48eda09c463 100644
--- a/llvm/lib/Transforms/Scalar/GuardWidening.cpp
+++ b/llvm/lib/Transforms/Scalar/GuardWidening.cpp
@@ -51,6 +51,7 @@
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/Scalar.h"
 
 using namespace llvm;
@@ -537,9 +538,9 @@ bool GuardWideningImpl::parseRangeChecks(
     } else if (match(Check.getBase(),
                      m_Or(m_Value(OpLHS), m_ConstantInt(OpRHS)))) {
       unsigned BitWidth = OpLHS->getType()->getScalarSizeInBits();
-      APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-      computeKnownBits(OpLHS, KnownZero, KnownOne, DL);
-      if ((OpRHS->getValue() & KnownZero) == OpRHS->getValue()) {
+      KnownBits Known(BitWidth);
+      computeKnownBits(OpLHS, Known, DL);
+      if ((OpRHS->getValue() & Known.Zero) == OpRHS->getValue()) {
         Check.setBase(OpLHS);
         APInt NewOffset = Check.getOffsetValue() + OpRHS->getValue();
         Check.setOffset(ConstantInt::get(Ctx, NewOffset));