[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
diff --git a/llvm/lib/Transforms/Scalar/GuardWidening.cpp b/llvm/lib/Transforms/Scalar/GuardWidening.cpp
index 7019287..48eda09 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 @@
} 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));