Use helper introduced in 8020be0 to simplify ValueTracking [NFC]

Direct rewrite of the code the helper was extracted from.

Author: preames

llvm/include/llvm/Analysis/ValueTracking.h

@@ -755,7 +755,7 @@ constexpr unsigned MaxAnalysisRecursionDepth = 6;
   ///   %inc = binop %iv, %step
   /// NOTE: This is intentional simple.  If you want the ability to analyze
   /// non-trivial loop conditons, see ScalarEvolution instead.
-  bool matchSimpleRecurrence(PHINode *P, BinaryOperator *&BO,
+  bool matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO,
                              Value *&Start, Value *&Step);
 
   /// Return true if RHS is known to be implied true by LHS.  Return false if

llvm/lib/Analysis/ValueTracking.cpp

@@ -1371,136 +1371,115 @@ static void computeKnownBitsFromOperator(const Operator *I,
   }
   case Instruction::PHI: {
     const PHINode *P = cast<PHINode>(I);
-    // Handle the case of a simple two-predecessor recurrence PHI.
-    // There's a lot more that could theoretically be done here, but
-    // this is sufficient to catch some interesting cases.
-    if (P->getNumIncomingValues() == 2) {
-      for (unsigned i = 0; i != 2; ++i) {
-        Value *L = P->getIncomingValue(i);
-        Value *R = P->getIncomingValue(!i);
-        Instruction *RInst = P->getIncomingBlock(!i)->getTerminator();
-        Instruction *LInst = P->getIncomingBlock(i)->getTerminator();
-        Operator *LU = dyn_cast<Operator>(L);
-        if (!LU)
-          continue;
-        unsigned Opcode = LU->getOpcode();
-
-
-        // If this is a shift recurrence, we know the bits being shifted in.
-        // We can combine that with information about the start value of the
-        // recurrence to conclude facts about the result.
-        if (Opcode == Instruction::LShr ||
-            Opcode == Instruction::AShr ||
-            Opcode == Instruction::Shl) {
-          Value *LL = LU->getOperand(0);
-          Value *LR = LU->getOperand(1);
-          // Find a recurrence.
-          if (LL == I)
-            L = LR;
-          else
-            continue; // Check for recurrence with L and R flipped.
-
-          // We have matched a recurrence of the form:
-          // %iv = [R, %entry], [%iv.next, %backedge]
-          // %iv.next = shift_op %iv, L
-
-          // Recurse with the phi context to avoid concern about whether facts
-          // inferred hold at original context instruction.  TODO: It may be
-          // correct to use the original context.  IF warranted, explore and
-          // add sufficient tests to cover.
-          Query RecQ = Q;
-          RecQ.CxtI = P;
-          computeKnownBits(R, DemandedElts, Known2, Depth + 1, RecQ);
-          switch (Opcode) {
-          case Instruction::Shl:
-            // A shl recurrence will only increase the tailing zeros
-            Known.Zero.setLowBits(Known2.countMinTrailingZeros());
-            break;
-          case Instruction::LShr:
-            // A lshr recurrence will preserve the leading zeros of the
-            // start value
-            Known.Zero.setHighBits(Known2.countMinLeadingZeros());
-            break;
-          case Instruction::AShr:
-            // An ashr recurrence will extend the initial sign bit
-            Known.Zero.setHighBits(Known2.countMinLeadingZeros());
-            Known.One.setHighBits(Known2.countMinLeadingOnes());
-            break;
-          };
-        }
+    BinaryOperator *BO = nullptr;
+    Value *R = nullptr, *L = nullptr;
+    if (matchSimpleRecurrence(P, BO, R, L)) {
+      // Handle the case of a simple two-predecessor recurrence PHI.
+      // There's a lot more that could theoretically be done here, but
+      // this is sufficient to catch some interesting cases.
+      unsigned Opcode = BO->getOpcode();
+
+      // If this is a shift recurrence, we know the bits being shifted in.
+      // We can combine that with information about the start value of the
+      // recurrence to conclude facts about the result.
+      if (Opcode == Instruction::LShr ||
+          Opcode == Instruction::AShr ||
+          Opcode == Instruction::Shl) {
+
+        // We have matched a recurrence of the form:
+        // %iv = [R, %entry], [%iv.next, %backedge]
+        // %iv.next = shift_op %iv, L
+
+        // Recurse with the phi context to avoid concern about whether facts
+        // inferred hold at original context instruction.  TODO: It may be
+        // correct to use the original context.  IF warranted, explore and
+        // add sufficient tests to cover.
+        Query RecQ = Q;
+        RecQ.CxtI = P;
+        computeKnownBits(R, DemandedElts, Known2, Depth + 1, RecQ);
+        switch (Opcode) {
+        case Instruction::Shl:
+          // A shl recurrence will only increase the tailing zeros
+          Known.Zero.setLowBits(Known2.countMinTrailingZeros());
+          break;
+        case Instruction::LShr:
+          // A lshr recurrence will preserve the leading zeros of the
+          // start value
+          Known.Zero.setHighBits(Known2.countMinLeadingZeros());
+          break;
+        case Instruction::AShr:
+          // An ashr recurrence will extend the initial sign bit
+          Known.Zero.setHighBits(Known2.countMinLeadingZeros());
+          Known.One.setHighBits(Known2.countMinLeadingOnes());
+          break;
+        };
+      }
 
-        // Check for operations that have the property that if
-        // both their operands have low zero bits, the result
-        // will have low zero bits.
-        if (Opcode == Instruction::Add ||
-            Opcode == Instruction::Sub ||
-            Opcode == Instruction::And ||
-            Opcode == Instruction::Or ||
-            Opcode == Instruction::Mul) {
-          Value *LL = LU->getOperand(0);
-          Value *LR = LU->getOperand(1);
-          // Find a recurrence.
-          if (LL == I)
-            L = LR;
-          else if (LR == I)
-            L = LL;
-          else
-            continue; // Check for recurrence with L and R flipped.
-
-          // Change the context instruction to the "edge" that flows into the
-          // phi. This is important because that is where the value is actually
-          // "evaluated" even though it is used later somewhere else. (see also
-          // D69571).
-          Query RecQ = Q;
-
-          // Ok, we have a PHI of the form L op= R. Check for low
-          // zero bits.
-          RecQ.CxtI = RInst;
-          computeKnownBits(R, Known2, Depth + 1, RecQ);
-
-          // We need to take the minimum number of known bits
-          KnownBits Known3(BitWidth);
-          RecQ.CxtI = LInst;
-          computeKnownBits(L, Known3, Depth + 1, RecQ);
-
-          Known.Zero.setLowBits(std::min(Known2.countMinTrailingZeros(),
-                                         Known3.countMinTrailingZeros()));
-
-          auto *OverflowOp = dyn_cast<OverflowingBinaryOperator>(LU);
-          if (OverflowOp && Q.IIQ.hasNoSignedWrap(OverflowOp)) {
-            // 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 (Known2.isNonNegative() && Known3.isNonNegative())
-                Known.makeNonNegative();
-              else if (Known2.isNegative() && Known3.isNegative())
-                Known.makeNegative();
-            }
-
-            // (sub nsw non-negative, negative) --> non-negative
-            // (sub nsw negative, non-negative) --> negative
-            else if (Opcode == Instruction::Sub && LL == I) {
-              if (Known2.isNonNegative() && Known3.isNegative())
-                Known.makeNonNegative();
-              else if (Known2.isNegative() && Known3.isNonNegative())
-                Known.makeNegative();
-            }
-
-            // (mul nsw non-negative, non-negative) --> non-negative
-            else if (Opcode == Instruction::Mul && Known2.isNonNegative() &&
-                     Known3.isNonNegative())
+      // Check for operations that have the property that if
+      // both their operands have low zero bits, the result
+      // will have low zero bits.
+      if (Opcode == Instruction::Add ||
+          Opcode == Instruction::Sub ||
+          Opcode == Instruction::And ||
+          Opcode == Instruction::Or ||
+          Opcode == Instruction::Mul) {
+        // Change the context instruction to the "edge" that flows into the
+        // phi. This is important because that is where the value is actually
+        // "evaluated" even though it is used later somewhere else. (see also
+        // D69571).
+        Query RecQ = Q;
+
+        unsigned OpNum = P->getOperand(0) == R ? 0 : 1;
+        Instruction *RInst = P->getIncomingBlock(OpNum)->getTerminator();
+        Instruction *LInst = P->getIncomingBlock(1-OpNum)->getTerminator();
+
+        // Ok, we have a PHI of the form L op= R. Check for low
+        // zero bits.
+        RecQ.CxtI = RInst;
+        computeKnownBits(R, Known2, Depth + 1, RecQ);
+
+        // We need to take the minimum number of known bits
+        KnownBits Known3(BitWidth);
+        RecQ.CxtI = LInst;
+        computeKnownBits(L, Known3, Depth + 1, RecQ);
+
+        Known.Zero.setLowBits(std::min(Known2.countMinTrailingZeros(),
+                                       Known3.countMinTrailingZeros()));
+
+        auto *OverflowOp = dyn_cast<OverflowingBinaryOperator>(BO);
+        if (OverflowOp && Q.IIQ.hasNoSignedWrap(OverflowOp)) {
+          // 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 (Known2.isNonNegative() && Known3.isNonNegative())
               Known.makeNonNegative();
+            else if (Known2.isNegative() && Known3.isNegative())
+              Known.makeNegative();
           }
 
-          break;
+          // (sub nsw non-negative, negative) --> non-negative
+          // (sub nsw negative, non-negative) --> negative
+          else if (Opcode == Instruction::Sub && BO->getOperand(0) == I) {
+            if (Known2.isNonNegative() && Known3.isNegative())
+              Known.makeNonNegative();
+            else if (Known2.isNegative() && Known3.isNonNegative())
+              Known.makeNegative();
+          }
+
+          // (mul nsw non-negative, non-negative) --> non-negative
+          else if (Opcode == Instruction::Mul && Known2.isNonNegative() &&
+                   Known3.isNonNegative())
+            Known.makeNonNegative();
         }
+
+        break;
       }
     }
 
@@ -6053,7 +6032,7 @@ llvm::canConvertToMinOrMaxIntrinsic(ArrayRef<Value *> VL) {
   return {Intrinsic::not_intrinsic, false};
 }
 
-bool llvm::matchSimpleRecurrence(PHINode *P, BinaryOperator *&BO,
+bool llvm::matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO,
                                  Value *&Start, Value *&Step) {
   // Handle the case of a simple two-predecessor recurrence PHI.
   // There's a lot more that could theoretically be done here, but