[KnownBits] Add methods for determining if KnownBits is a constant value

This patch adds isConstant and getConstant for determining if KnownBits represents a constant value and to retrieve the value. Use them to simplify code.

Differential Revision: https://reviews.llvm.org/D32785

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302091 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/KnownBits.h

@@ -43,6 +43,22 @@ struct KnownBits {
     return Zero.getBitWidth();
   }
 
+  /// Returns true if there is conflicting information.
+  bool hasConflict() const { return Zero.intersects(One); }
+
+  /// Returns true if we know the value of all bits.
+  bool isConstant() const {
+    assert(!hasConflict() && "KnownBits conflict!");
+    return Zero.countPopulation() + One.countPopulation() == getBitWidth();
+  }
+
+  /// Returns the value when all bits have a known value. This just returns One
+  /// with a protective assertion.
+  const APInt &getConstant() const {
+    assert(isConstant() && "Can only get value when all bits are known");
+    return One;
+  }
+
   /// Returns true if this value is known to be negative.
   bool isNegative() const { return One.isSignBitSet(); }
 

lib/Analysis/ConstantFolding.cpp

@@ -701,11 +701,10 @@ Constant *SymbolicallyEvaluateBinop(unsigned Opc, Constant *Op0, Constant *Op1,
       return Op1;
     }
 
-    APInt KnownZero = Known0.Zero | Known1.Zero;
-    APInt KnownOne = Known0.One & Known1.One;
-    if ((KnownZero | KnownOne).isAllOnesValue()) {
-      return ConstantInt::get(Op0->getType(), KnownOne);
-    }
+    Known0.Zero |= Known1.Zero;
+    Known0.One &= Known1.One;
+    if (Known0.isConstant())
+      return ConstantInt::get(Op0->getType(), Known0.getConstant());
   }
 
   // If the constant expr is something like &A[123] - &A[4].f, fold this into a

lib/Analysis/InstructionSimplify.cpp

@@ -4595,8 +4595,8 @@ Value *llvm::SimplifyInstruction(Instruction *I, const SimplifyQuery &SQ,
     unsigned BitWidth = I->getType()->getScalarSizeInBits();
     KnownBits Known(BitWidth);
     computeKnownBits(I, Known, Q.DL, /*Depth*/ 0, Q.AC, I, Q.DT, ORE);
-    if ((Known.Zero | Known.One).isAllOnesValue())
-      Result = ConstantInt::get(I->getType(), Known.One);
+    if (Known.isConstant())
+      Result = ConstantInt::get(I->getType(), Known.getConstant());
   }
 
   /// If called on unreachable code, the above logic may report that the

lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -2182,8 +2182,8 @@ Instruction *InstCombiner::visitReturnInst(ReturnInst &RI) {
   // determine the value. If so, constant fold it.
   KnownBits Known(VTy->getPrimitiveSizeInBits());
   computeKnownBits(ResultOp, Known, 0, &RI);
-  if ((Known.Zero|Known.One).isAllOnesValue())
-    RI.setOperand(0, Constant::getIntegerValue(VTy, Known.One));
+  if (Known.isConstant())
+    RI.setOperand(0, Constant::getIntegerValue(VTy, Known.getConstant()));
 
   return nullptr;
 }
@@ -2863,8 +2863,8 @@ bool InstCombiner::run() {
       unsigned BitWidth = Ty->getScalarSizeInBits();
       KnownBits Known(BitWidth);
       computeKnownBits(I, Known, /*Depth*/0, I);
-      if ((Known.Zero | Known.One).isAllOnesValue()) {
-        Constant *C = ConstantInt::get(Ty, Known.One);
+      if (Known.isConstant()) {
+        Constant *C = ConstantInt::get(Ty, Known.getConstant());
         DEBUG(dbgs() << "IC: ConstFold (all bits known) to: " << *C <<
                         " from: " << *I << '\n');