[ValueTracking] Use APInt::isNegative instead of using operator[BitWi…

…dth-1]. NFCI

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298584 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ValueTracking.cpp

@@ -993,17 +993,17 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
     unsigned MaxHighZeros = 0;
     if (SPF == SPF_SMAX) {
       // If both sides are negative, the result is negative.
-      if (KnownOne[BitWidth - 1] && KnownOne2[BitWidth - 1])
+      if (KnownOne.isNegative() && KnownOne2.isNegative())
         // We can derive a lower bound on the result by taking the max of the
         // leading one bits.
         MaxHighOnes =
             std::max(KnownOne.countLeadingOnes(), KnownOne2.countLeadingOnes());
       // If either side is non-negative, the result is non-negative.
-      else if (KnownZero[BitWidth - 1] || KnownZero2[BitWidth - 1])
+      else if (KnownZero.isNegative() || KnownZero2.isNegative())
         MaxHighZeros = 1;
     } else if (SPF == SPF_SMIN) {
       // If both sides are non-negative, the result is non-negative.
-      if (KnownZero[BitWidth - 1] && KnownZero2[BitWidth - 1])
+      if (KnownZero.isNegative() && KnownZero2.isNegative())
         // We can derive an upper bound on the result by taking the max of the
         // leading zero bits.
         MaxHighZeros = std::max(KnownZero.countLeadingOnes(),
@@ -1177,12 +1177,12 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
 
         // If the first operand is non-negative or has all low bits zero, then
         // the upper bits are all zero.
-        if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
+        if (KnownZero2.isNegative() || ((KnownZero2 & LowBits) == LowBits))
           KnownZero |= ~LowBits;
 
         // If the first operand is negative and not all low bits are zero, then
         // the upper bits are all one.
-        if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
+        if (KnownOne2.isNegative() && ((KnownOne2 & LowBits) != 0))
           KnownOne |= ~LowBits;
 
         assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
@@ -1626,8 +1626,8 @@ void ComputeSignBit(const Value *V, bool &KnownZero, bool &KnownOne,
   APInt ZeroBits(BitWidth, 0);
   APInt OneBits(BitWidth, 0);
   computeKnownBits(V, ZeroBits, OneBits, Depth, Q);
-  KnownOne = OneBits[BitWidth - 1];
-  KnownZero = ZeroBits[BitWidth - 1];
+  KnownOne = OneBits.isNegative();
+  KnownZero = ZeroBits.isNegative();
 }
 
 /// Return true if the given value is known to have exactly one