Revert "[ValueTracking] Teach computeKnownBits for PHI nodes to compute sign bit for a recurrence with a NSW addition."

This is breaking an optimizaton remark test in clang. I've identified a couple fixes for that, but want to understand it better before I commit to anything.

llvm-svn: 274102

1 files changed, 0 insertions, 12 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 78ec220..16dd307 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1240,18 +1240,6 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero,
           KnownZero = APInt::getLowBitsSet(BitWidth,
                                            std::min(KnownZero2.countTrailingOnes(),
                                                     KnownZero3.countTrailingOnes()));
-
-          // If the operation is an addition that can't have signed overflow,
-          // then the sign bit is known to be zero if both input sign bits
-          // are zero. Similar for two negative inputs.
-          if (Opcode == Instruction::Add &&
-              cast<OverflowingBinaryOperator>(LU)->hasNoSignedWrap()) {
-            if (KnownZero2.isNegative() && KnownZero3.isNegative())
-              KnownZero.setBit(BitWidth-1);
-            if (KnownOne2.isNegative() && KnownOne3.isNegative())
-              KnownOne.setBit(BitWidth-1);
-          }
-
           break;
         }
       }