[llvm] r298190 - [ValueTracking] Remove deadish code from computeKnownBitsAddSub.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Sat Mar 18 13:21:46 2017
New Revision: 298190

URL: http://llvm.org/viewvc/llvm-project?rev=298190&view=rev
Log:
[ValueTracking] Remove deadish code from computeKnownBitsAddSub.

The code assigned to KnownZero, but later code unconditionally assigned over it. I'm pretty sure the later code can handle the same cases and more equally well.

Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=298190&r1=298189&r2=298190&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Sat Mar 18 13:21:46 2017
@@ -255,30 +255,6 @@ static void computeKnownBitsAddSub(bool
                                    APInt &KnownZero, APInt &KnownOne,
                                    APInt &KnownZero2, APInt &KnownOne2,
                                    unsigned Depth, const Query &Q) {
-  if (!Add) {
-    if (const ConstantInt *CLHS = dyn_cast<ConstantInt>(Op0)) {
-      // We know that the top bits of C-X are clear if X contains less bits
-      // than C (i.e. no wrap-around can happen).  For example, 20-X is
-      // positive if we can prove that X is >= 0 and < 16.
-      if (!CLHS->getValue().isNegative()) {
-        unsigned BitWidth = KnownZero.getBitWidth();
-        unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
-        // NLZ can't be BitWidth with no sign bit
-        APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
-        computeKnownBits(Op1, KnownZero2, KnownOne2, Depth + 1, Q);
-
-        // If all of the MaskV bits are known to be zero, then we know the
-        // output top bits are zero, because we now know that the output is
-        // from [0-C].
-        if ((KnownZero2 & MaskV) == MaskV) {
-          unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
-          // Top bits known zero.
-          KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2);
-        }
-      }
-    }
-  }
-
   unsigned BitWidth = KnownZero.getBitWidth();
 
   // If an initial sequence of bits in the result is not needed, the