[ValueTracking] Recognize that and(x, add (x, -1)) clears the low bit

[oota-llvm.git] / lib / Analysis / ValueTracking.cpp

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index f4824aebe525610a5197aa5bc102e0f88bc8193b..8d39e4e542db2e979043da91b7c1c6587bd64e30 100644 (file)
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -1077,6 +1077,22 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero,
     KnownOne &= KnownOne2;
     // Output known-0 are known to be clear if zero in either the LHS | RHS.
     KnownZero |= KnownZero2;
+
+    // and(x, add (x, -1)) is a common idiom that always clears the low bit;
+    // here we handle the more general case of adding any odd number by
+    // matching the form add(x, add(x, y)) where y is odd.
+    // TODO: This could be generalized to clearing any bit set in y where the
+    // following bit is known to be unset in y.
+    Value *Y = nullptr;
+    if (match(I->getOperand(0), m_Add(m_Specific(I->getOperand(1)),
+                                      m_Value(Y))) ||
+        match(I->getOperand(1), m_Add(m_Specific(I->getOperand(0)),
+                                      m_Value(Y)))) {
+      APInt KnownZero3(BitWidth, 0), KnownOne3(BitWidth, 0);
+      computeKnownBits(Y, KnownZero3, KnownOne3, DL, Depth + 1, Q);
+      if (KnownOne3.countTrailingOnes() > 0)
+        KnownZero |= APInt::getLowBitsSet(BitWidth, 1);
+    }
     break;
   }
   case Instruction::Or: {
@@ -4083,7 +4099,10 @@ ConstantRange llvm::getConstantRangeFromMetadata(MDNode &Ranges) {
 }
 
 /// Return true if "icmp Pred LHS RHS" is always true.
-static bool isTruePredicate(CmpInst::Predicate Pred, Value *LHS, Value *RHS) {
+static bool isTruePredicate(CmpInst::Predicate Pred, Value *LHS, Value *RHS,
+                            const DataLayout &DL, unsigned Depth,
+                            AssumptionCache *AC, const Instruction *CxtI,
+                            const DominatorTree *DT) {
   if (ICmpInst::isTrueWhenEqual(Pred) && LHS == RHS)
     return true;
 
@@ -4124,24 +4143,34 @@ static bool isTruePredicate(CmpInst::Predicate Pred, Value *LHS, Value *RHS) {
 /// Return true if "icmp Pred BLHS BRHS" is true whenever "icmp Pred
 /// ALHS ARHS" is true.
 static bool isImpliedCondOperands(CmpInst::Predicate Pred, Value *ALHS,
-                                  Value *ARHS, Value *BLHS, Value *BRHS) {
+                                  Value *ARHS, Value *BLHS, Value *BRHS,
+                                  const DataLayout &DL, unsigned Depth,
+                                  AssumptionCache *AC, const Instruction *CxtI,
+                                  const DominatorTree *DT) {
   switch (Pred) {
   default:
     return false;
 
   case CmpInst::ICMP_SLT:
   case CmpInst::ICMP_SLE:
-    return isTruePredicate(CmpInst::ICMP_SLE, BLHS, ALHS) &&
-           isTruePredicate(CmpInst::ICMP_SLE, ARHS, BRHS);
+    return isTruePredicate(CmpInst::ICMP_SLE, BLHS, ALHS, DL, Depth, AC, CxtI,
+                           DT) &&
+           isTruePredicate(CmpInst::ICMP_SLE, ARHS, BRHS, DL, Depth, AC, CxtI,
+                           DT);
 
   case CmpInst::ICMP_ULT:
   case CmpInst::ICMP_ULE:
-    return isTruePredicate(CmpInst::ICMP_ULE, BLHS, ALHS) &&
-           isTruePredicate(CmpInst::ICMP_ULE, ARHS, BRHS);
+    return isTruePredicate(CmpInst::ICMP_ULE, BLHS, ALHS, DL, Depth, AC, CxtI,
+                           DT) &&
+           isTruePredicate(CmpInst::ICMP_ULE, ARHS, BRHS, DL, Depth, AC, CxtI,
+                           DT);
   }
 }
 
-bool llvm::isImpliedCondition(Value *LHS, Value *RHS) {
+bool llvm::isImpliedCondition(Value *LHS, Value *RHS, const DataLayout &DL,
+                              unsigned Depth, AssumptionCache *AC,
+                              const Instruction *CxtI,
+                              const DominatorTree *DT) {
   assert(LHS->getType() == RHS->getType() && "mismatched type");
   Type *OpTy = LHS->getType();
   assert(OpTy->getScalarType()->isIntegerTy(1));
@@ -4163,7 +4192,8 @@ bool llvm::isImpliedCondition(Value *LHS, Value *RHS) {
     return false;
 
   if (APred == BPred)
-    return isImpliedCondOperands(APred, ALHS, ARHS, BLHS, BRHS);
+    return isImpliedCondOperands(APred, ALHS, ARHS, BLHS, BRHS, DL, Depth, AC,
+                                 CxtI, DT);
 
   return false;
 }