[llvm] r279433 - Revert -r278267 [ValueTracking] An improvement to IR ValueTracking on Non-negative Integers

[Artur Pilipenko via llvm-commits]

Author: apilipenko
Date: Mon Aug 22 08:14:07 2016
New Revision: 279433

URL: http://llvm.org/viewvc/llvm-project?rev=279433&view=rev
Log:
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.

Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp
    llvm/trunk/test/Transforms/BBVectorize/loop1.ll

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=279433&r1=279432&r2=279433&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Mon Aug 22 08:14:07 2016
@@ -1259,9 +1259,7 @@ static void computeKnownBitsFromOperator
         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
           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;
         }
       }

Modified: llvm/trunk/test/Transforms/BBVectorize/loop1.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/BBVectorize/loop1.ll?rev=279433&r1=279432&r2=279433&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/BBVectorize/loop1.ll (original)
+++ llvm/trunk/test/Transforms/BBVectorize/loop1.ll Mon Aug 22 08:14:07 2016
@@ -83,7 +83,7 @@ for.body:
 ; CHECK-UNRL: %add12 = fadd <2 x double> %add7, %mul11
 ; CHECK-UNRL: %4 = bitcast double* %arrayidx14 to <2 x double>*
 ; CHECK-UNRL: store <2 x double> %add12, <2 x double>* %4, align 8
-; CHECK-UNRL: %indvars.iv.next.1 = add nuw nsw i64 %indvars.iv, 2
+; CHECK-UNRL: %indvars.iv.next.1 = add nsw i64 %indvars.iv, 2
 ; CHECK-UNRL: %lftr.wideiv.1 = trunc i64 %indvars.iv.next.1 to i32
 ; CHECK-UNRL: %exitcond.1 = icmp eq i32 %lftr.wideiv.1, 10
 ; CHECK-UNRL: br i1 %exitcond.1, label %for.end, label %for.body