Revert -r278267 [ValueTracking] An improvement to IR ValueTracking on Non-negative Integers

This change cause performance regression on MultiSource/Benchmarks/TSVC/Symbolics-flt/Symbolics-flt from LNT and some other bechmarks.

See https://reviews.llvm.org/D18777 for details.

llvm-svn: 279433

1 files changed, 1 insertions, 37 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 48305f4..c9fc4d4 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1259,9 +1259,7 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
         unsigned Opcode = LU->getOpcode();
         // Check for operations that have the property that if
         // both their operands have low zero bits, the result
-        // will have low zero bits. Also check for operations 
-        // that are known to produce non-negative or negative
-        // recurrence values. 
+        // will have low zero bits.
         if (Opcode == Instruction::Add ||
             Opcode == Instruction::Sub ||
             Opcode == Instruction::And ||
@@ -1287,40 +1285,6 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
           KnownZero = APInt::getLowBitsSet(BitWidth,
                                            std::min(KnownZero2.countTrailingOnes(),
                                                     KnownZero3.countTrailingOnes()));
-
-          auto *OverflowOp = dyn_cast<OverflowingBinaryOperator>(LU);
-          if (OverflowOp && OverflowOp->hasNoSignedWrap()) {
-            // If initial value of recurrence is nonnegative, and we are adding 
-            // a nonnegative number with nsw, the result can only be nonnegative
-            // or poison value regardless of the number of times we execute the 
-            // add in phi recurrence. If initial value is negative and we are 
-            // adding a negative number with nsw, the result can only be 
-            // negative or poison value. Similar arguments apply to sub and mul.
-            //
-            // (add non-negative, non-negative) --> non-negative
-            // (add negative, negative) --> negative
-            if (Opcode == Instruction::Add) {
-              if (KnownZero2.isNegative() && KnownZero3.isNegative())
-                KnownZero.setBit(BitWidth - 1);
-              else if (KnownOne2.isNegative() && KnownOne3.isNegative())
-                KnownOne.setBit(BitWidth - 1);
-            }
-            
-            // (sub nsw non-negative, negative) --> non-negative
-            // (sub nsw negative, non-negative) --> negative
-            else if (Opcode == Instruction::Sub && LL == I) {
-              if (KnownZero2.isNegative() && KnownOne3.isNegative())
-                KnownZero.setBit(BitWidth - 1);
-              else if (KnownOne2.isNegative() && KnownZero3.isNegative())
-                KnownOne.setBit(BitWidth - 1);
-            }
-            
-            // (mul nsw non-negative, non-negative) --> non-negative
-            else if (Opcode == Instruction::Mul && KnownZero2.isNegative() && 
-                     KnownZero3.isNegative())
-              KnownZero.setBit(BitWidth - 1);
-          }
-
           break;
         }
       }