[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, 5 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Utils/BypassSlowDivision.cpp b/llvm/lib/Transforms/Utils/BypassSlowDivision.cpp
index 1cfe3bd5364..7ffdad597a9 100644
--- a/llvm/lib/Transforms/Utils/BypassSlowDivision.cpp
+++ b/llvm/lib/Transforms/Utils/BypassSlowDivision.cpp
@@ -22,6 +22,7 @@
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/Utils/Local.h"
 
 using namespace llvm;
@@ -256,14 +257,14 @@ ValueRange FastDivInsertionTask::getValueRange(Value *V,
   unsigned HiBits = LongLen - ShortLen;
 
   const DataLayout &DL = SlowDivOrRem->getModule()->getDataLayout();
-  APInt Zeros(LongLen, 0), Ones(LongLen, 0);
+  KnownBits Known(LongLen);
 
-  computeKnownBits(V, Zeros, Ones, DL);
+  computeKnownBits(V, Known, DL);
 
-  if (Zeros.countLeadingOnes() >= HiBits)
+  if (Known.Zero.countLeadingOnes() >= HiBits)
     return VALRNG_KNOWN_SHORT;
 
-  if (Ones.countLeadingZeros() < HiBits)
+  if (Known.One.countLeadingZeros() < HiBits)
     return VALRNG_LIKELY_LONG;
 
   // Long integer divisions are often used in hashtable implementations. It's