[NFC][InstCombine] Moving overflow computation logic from InstCombine to ValueTracking

[opaparo]

Summary

Moving the overflow computation logic of signed mul and un/signed sub from the internals of InstCombine to ValueTracking (where it can be widely used).

[spatel]

LGTM.

[spatel]

lib/Analysis/ValueTracking.cpp

3706–3711 ↗

(On Diff #146149)

Formatting looks off - run clang-format.

llvm/trunk/include/llvm/Analysis/ValueTracking.h

class Value;
   enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
 
   OverflowResult computeOverflowForUnsignedMul(const Value *LHS,
                                                const Value *RHS,
                                                const DataLayout &DL,
                                                AssumptionCache *AC,
                                                const Instruction *CxtI,
                                                const DominatorTree *DT);
+  OverflowResult computeOverflowForSignedMul(const Value *LHS, const Value *RHS,
+                                             const DataLayout &DL,
+                                             AssumptionCache *AC,
+                                             const Instruction *CxtI,
+                                             const DominatorTree *DT);
   OverflowResult computeOverflowForUnsignedAdd(const Value *LHS,
                                                const Value *RHS,
                                                const DataLayout &DL,
                                                AssumptionCache *AC,
                                                const Instruction *CxtI,
                                                const DominatorTree *DT);
   OverflowResult computeOverflowForSignedAdd(const Value *LHS, const Value *RHS,
                                              const DataLayout &DL,
                                              AssumptionCache *AC = nullptr,
                                              const Instruction *CxtI = nullptr,
                                              const DominatorTree *DT = nullptr);
   /// This version also leverages the sign bit of Add if known.
   OverflowResult computeOverflowForSignedAdd(const AddOperator *Add,
                                              const DataLayout &DL,
                                              AssumptionCache *AC = nullptr,
                                              const Instruction *CxtI = nullptr,
                                              const DominatorTree *DT = nullptr);
+  OverflowResult computeOverflowForUnsignedSub(const Value *LHS, const Value *RHS,
+                                               const DataLayout &DL,
+                                               AssumptionCache *AC,
+                                               const Instruction *CxtI,
+                                               const DominatorTree *DT);
+  OverflowResult computeOverflowForSignedSub(const Value *LHS, const Value *RHS,
+                                             const DataLayout &DL,
+                                             AssumptionCache *AC,
+                                             const Instruction *CxtI,
+                                             const DominatorTree *DT);
 
   /// Returns true if the arithmetic part of the \p II 's result is
   /// used only along the paths control dependent on the computation
   /// not overflowing, \p II being an <op>.with.overflow intrinsic.
   bool isOverflowIntrinsicNoWrap(const IntrinsicInst *II,
                                  const DominatorTree &DT);
 
   /// Return true if this function can prove that the instruction I will

llvm/trunk/lib/Analysis/ValueTracking.cpp

OverflowResult llvm::computeOverflowForUnsignedMul(const Value *LHS,
   bool MinOverflow;
   (void)LHSKnown.One.umul_ov(RHSKnown.One, MinOverflow);
   if (MinOverflow)
     return OverflowResult::AlwaysOverflows;
 
   return OverflowResult::MayOverflow;
 }
 
+OverflowResult llvm::computeOverflowForSignedMul(const Value *LHS,
+                                                 const Value *RHS,
+                                                 const DataLayout &DL,
+                                                 AssumptionCache *AC,
+                                                 const Instruction *CxtI,
+                                                 const DominatorTree *DT) {
+  // Multiplying n * m significant bits yields a result of n + m significant
+  // bits. If the total number of significant bits does not exceed the
+  // result bit width (minus 1), there is no overflow.
+  // This means if we have enough leading sign bits in the operands
+  // we can guarantee that the result does not overflow.
+  // Ref: "Hacker's Delight" by Henry Warren
+  unsigned BitWidth = LHS->getType()->getScalarSizeInBits();
+
+  // Note that underestimating the number of sign bits gives a more
+  // conservative answer.
+  unsigned SignBits = ComputeNumSignBits(LHS, DL, 0, AC, CxtI, DT) +
+                      ComputeNumSignBits(RHS, DL, 0, AC, CxtI, DT);
+
+  // First handle the easy case: if we have enough sign bits there's
+  // definitely no overflow.
+  if (SignBits > BitWidth + 1)
+    return OverflowResult::NeverOverflows;
+
+  // There are two ambiguous cases where there can be no overflow:
+  //   SignBits == BitWidth + 1    and
+  //   SignBits == BitWidth
+  // The second case is difficult to check, therefore we only handle the
+  // first case.
+  if (SignBits == BitWidth + 1) {
+    // It overflows only when both arguments are negative and the true
+    // product is exactly the minimum negative number.
+    // E.g. mul i16 with 17 sign bits: 0xff00 * 0xff80 = 0x8000
+    // For simplicity we just check if at least one side is not negative.
+    KnownBits LHSKnown = computeKnownBits(LHS, DL, /*Depth=*/0, AC, CxtI, DT);
+    KnownBits RHSKnown = computeKnownBits(RHS, DL, /*Depth=*/0, AC, CxtI, DT);
+    if (LHSKnown.isNonNegative() || RHSKnown.isNonNegative())
+      return OverflowResult::NeverOverflows;
+  }
+  return OverflowResult::MayOverflow;
+}
+
 OverflowResult llvm::computeOverflowForUnsignedAdd(const Value *LHS,
                                                    const Value *RHS,
                                                    const DataLayout &DL,
                                                    AssumptionCache *AC,
                                                    const Instruction *CxtI,
                                                    const DominatorTree *DT) {
   KnownBits LHSKnown = computeKnownBits(LHS, DL, /*Depth=*/0, AC, CxtI, DT);
   if (LHSKnown.isNonNegative() || LHSKnown.isNegative()) {
if ((AddKnown.isNonNegative() && LHSOrRHSKnownNonNegative) ||
         (AddKnown.isNegative() && LHSOrRHSKnownNegative)) {
       return OverflowResult::NeverOverflows;
     }
   }
 
   return OverflowResult::MayOverflow;
 }
 
+OverflowResult llvm::computeOverflowForUnsignedSub(const Value *LHS,
+                                                   const Value *RHS,
+                                                   const DataLayout &DL,
+                                                   AssumptionCache *AC,
+                                                   const Instruction *CxtI,
+                                                   const DominatorTree *DT) {
+  // If the LHS is negative and the RHS is non-negative, no unsigned wrap.
+  KnownBits LHSKnown = computeKnownBits(LHS, DL, /*Depth=*/0, AC, CxtI, DT);
+  KnownBits RHSKnown = computeKnownBits(RHS, DL, /*Depth=*/0, AC, CxtI, DT);
+  if (LHSKnown.isNegative() && RHSKnown.isNonNegative())
+    return OverflowResult::NeverOverflows;
+
+  return OverflowResult::MayOverflow;
+}
+
+OverflowResult llvm::computeOverflowForSignedSub(const Value *LHS,
+                                                 const Value *RHS,
+                                                 const DataLayout &DL,
+                                                 AssumptionCache *AC,
+                                                 const Instruction *CxtI,
+                                                 const DominatorTree *DT) {
+  // If LHS and RHS each have at least two sign bits, the subtraction
+  // cannot overflow.
+  if (ComputeNumSignBits(LHS, DL, 0, AC, CxtI, DT) > 1 &&
+      ComputeNumSignBits(RHS, DL, 0, AC, CxtI, DT) > 1)
+    return OverflowResult::NeverOverflows;
+
+  KnownBits LHSKnown = computeKnownBits(LHS, DL, 0, AC, CxtI, DT);
+
+  KnownBits RHSKnown = computeKnownBits(RHS, DL, 0, AC, CxtI, DT);
+
+  // Subtraction of two 2's complement numbers having identical signs will
+  // never overflow.
+  if ((LHSKnown.isNegative() && RHSKnown.isNegative()) ||
+      (LHSKnown.isNonNegative() && RHSKnown.isNonNegative()))
+    return OverflowResult::NeverOverflows;
+
+  // TODO: implement logic similar to checkRippleForAdd
+  return OverflowResult::MayOverflow;
+}
+
 bool llvm::isOverflowIntrinsicNoWrap(const IntrinsicInst *II,
                                      const DominatorTree &DT) {
 #ifndef NDEBUG
   auto IID = II->getIntrinsicID();
   assert((IID == Intrinsic::sadd_with_overflow ||
           IID == Intrinsic::uadd_with_overflow ||
           IID == Intrinsic::ssub_with_overflow ||
           IID == Intrinsic::usub_with_overflow ||

llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp

if (Coeff.isTwo() || Coeff.isMinusTwo()) {
     NeedNeg = Coeff.isMinusTwo();
     return createFAdd(OpndVal, OpndVal);
   }
 
   NeedNeg = false;
   return createFMul(OpndVal, Coeff.getValue(Instr->getType()));
 }
 
-/// Return true if we can prove that:
-///    (sub LHS, RHS)  === (sub nsw LHS, RHS)
-/// This basically requires proving that the add in the original type would not
-/// overflow to change the sign bit or have a carry out.
-/// TODO: Handle this for Vectors.
-bool InstCombiner::willNotOverflowSignedSub(const Value *LHS,
-                                            const Value *RHS,
-                                            const Instruction &CxtI) const {
-  // If LHS and RHS each have at least two sign bits, the subtraction
-  // cannot overflow.
-  if (ComputeNumSignBits(LHS, 0, &CxtI) > 1 &&
-      ComputeNumSignBits(RHS, 0, &CxtI) > 1)
-    return true;
-
-  KnownBits LHSKnown = computeKnownBits(LHS, 0, &CxtI);
-
-  KnownBits RHSKnown = computeKnownBits(RHS, 0, &CxtI);
-
-  // Subtraction of two 2's complement numbers having identical signs will
-  // never overflow.
-  if ((LHSKnown.isNegative() && RHSKnown.isNegative()) ||
-      (LHSKnown.isNonNegative() && RHSKnown.isNonNegative()))
-    return true;
-
-  // TODO: implement logic similar to checkRippleForAdd
-  return false;
-}
-
-/// Return true if we can prove that:
-///    (sub LHS, RHS)  === (sub nuw LHS, RHS)
-bool InstCombiner::willNotOverflowUnsignedSub(const Value *LHS,
-                                              const Value *RHS,
-                                              const Instruction &CxtI) const {
-  // If the LHS is negative and the RHS is non-negative, no unsigned wrap.
-  KnownBits LHSKnown = computeKnownBits(LHS, /*Depth=*/0, &CxtI);
-  KnownBits RHSKnown = computeKnownBits(RHS, /*Depth=*/0, &CxtI);
-  if (LHSKnown.isNegative() && RHSKnown.isNonNegative())
-    return true;
-
-  return false;
-}
-
 // Checks if any operand is negative and we can convert add to sub.
 // This function checks for following negative patterns
 //   ADD(XOR(OR(Z, NOT(C)), C)), 1) == NEG(AND(Z, C))
 //   ADD(XOR(AND(Z, C), C), 1) == NEG(OR(Z, ~C))
 //   XOR(AND(Z, C), (C + 1)) == NEG(OR(Z, ~C)) if C is even
 static Value *checkForNegativeOperand(BinaryOperator &I,
                                       InstCombiner::BuilderTy &Builder) {
   Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);

llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h

private:
 
   bool willNotOverflowUnsignedAdd(const Value *LHS, const Value *RHS,
                                   const Instruction &CxtI) const {
     return computeOverflowForUnsignedAdd(LHS, RHS, &CxtI) ==
            OverflowResult::NeverOverflows;
   }
 
   bool willNotOverflowSignedSub(const Value *LHS, const Value *RHS,
-                                const Instruction &CxtI) const;
+                                const Instruction &CxtI) const {
+    return computeOverflowForSignedSub(LHS, RHS, &CxtI) ==
+           OverflowResult::NeverOverflows;
+  }
+
   bool willNotOverflowUnsignedSub(const Value *LHS, const Value *RHS,
-                                  const Instruction &CxtI) const;
+                                  const Instruction &CxtI) const {
+    return computeOverflowForUnsignedSub(LHS, RHS, &CxtI) ==
+           OverflowResult::NeverOverflows;
+  }
+
   bool willNotOverflowSignedMul(const Value *LHS, const Value *RHS,
-                                const Instruction &CxtI) const;
+                                const Instruction &CxtI) const {
+    return computeOverflowForSignedMul(LHS, RHS, &CxtI) ==
+           OverflowResult::NeverOverflows;
+  }
 
   bool willNotOverflowUnsignedMul(const Value *LHS, const Value *RHS,
                                   const Instruction &CxtI) const {
     return computeOverflowForUnsignedMul(LHS, RHS, &CxtI) ==
            OverflowResult::NeverOverflows;
   }
 
   Value *EmitGEPOffset(User *GEP);
public:
   }
 
   OverflowResult computeOverflowForUnsignedMul(const Value *LHS,
                                                const Value *RHS,
                                                const Instruction *CxtI) const {
     return llvm::computeOverflowForUnsignedMul(LHS, RHS, DL, &AC, CxtI, &DT);
   }
 
+  OverflowResult computeOverflowForSignedMul(const Value *LHS,
+                                           const Value *RHS,
+                                             const Instruction *CxtI) const {
+    return llvm::computeOverflowForSignedMul(LHS, RHS, DL, &AC, CxtI, &DT);
+  }
+
   OverflowResult computeOverflowForUnsignedAdd(const Value *LHS,
                                                const Value *RHS,
                                                const Instruction *CxtI) const {
     return llvm::computeOverflowForUnsignedAdd(LHS, RHS, DL, &AC, CxtI, &DT);
   }
 
   OverflowResult computeOverflowForSignedAdd(const Value *LHS,
                                              const Value *RHS,
                                              const Instruction *CxtI) const {
     return llvm::computeOverflowForSignedAdd(LHS, RHS, DL, &AC, CxtI, &DT);
   }
 
+  OverflowResult computeOverflowForUnsignedSub(const Value *LHS,
+                                               const Value *RHS,
+                                               const Instruction *CxtI) const {
+    return llvm::computeOverflowForUnsignedSub(LHS, RHS, DL, &AC, CxtI, &DT);
+  }
+
+  OverflowResult computeOverflowForSignedSub(const Value *LHS, const Value *RHS,
+                                             const Instruction *CxtI) const {
+    return llvm::computeOverflowForSignedSub(LHS, RHS, DL, &AC, CxtI, &DT);
+  }
+
   /// Maximum size of array considered when transforming.
   uint64_t MaxArraySizeForCombine;
 
 private:
   /// Performs a few simplifications for operators which are associative
   /// or commutative.
   bool SimplifyAssociativeOrCommutative(BinaryOperator &I);
 

llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

for (unsigned I = 0, E = Ty->getVectorNumElements(); I != E; ++I) {
     if (!match(Elt, m_APInt(IVal)) || !IVal->isPowerOf2())
       return nullptr;
     Elts.push_back(ConstantInt::get(Ty->getScalarType(), IVal->logBase2()));
   }
 
   return ConstantVector::get(Elts);
 }
 
-/// Return true if we can prove that:
-///    (mul LHS, RHS)  === (mul nsw LHS, RHS)
-bool InstCombiner::willNotOverflowSignedMul(const Value *LHS,
-                                            const Value *RHS,
-                                            const Instruction &CxtI) const {
-  // Multiplying n * m significant bits yields a result of n + m significant
-  // bits. If the total number of significant bits does not exceed the
-  // result bit width (minus 1), there is no overflow.
-  // This means if we have enough leading sign bits in the operands
-  // we can guarantee that the result does not overflow.
-  // Ref: "Hacker's Delight" by Henry Warren
-  unsigned BitWidth = LHS->getType()->getScalarSizeInBits();
-
-  // Note that underestimating the number of sign bits gives a more
-  // conservative answer.
-  unsigned SignBits =
-      ComputeNumSignBits(LHS, 0, &CxtI) + ComputeNumSignBits(RHS, 0, &CxtI);
-
-  // First handle the easy case: if we have enough sign bits there's
-  // definitely no overflow.
-  if (SignBits > BitWidth + 1)
-    return true;
-
-  // There are two ambiguous cases where there can be no overflow:
-  //   SignBits == BitWidth + 1    and
-  //   SignBits == BitWidth
-  // The second case is difficult to check, therefore we only handle the
-  // first case.
-  if (SignBits == BitWidth + 1) {
-    // It overflows only when both arguments are negative and the true
-    // product is exactly the minimum negative number.
-    // E.g. mul i16 with 17 sign bits: 0xff00 * 0xff80 = 0x8000
-    // For simplicity we just check if at least one side is not negative.
-    KnownBits LHSKnown = computeKnownBits(LHS, /*Depth=*/0, &CxtI);
-    KnownBits RHSKnown = computeKnownBits(RHS, /*Depth=*/0, &CxtI);
-    if (LHSKnown.isNonNegative() || RHSKnown.isNonNegative())
-      return true;
-  }
-  return false;
-}
-
 Instruction *InstCombiner::visitMul(BinaryOperator &I) {
   bool Changed = SimplifyAssociativeOrCommutative(I);
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 
   if (Value *V = SimplifyVectorOp(I))
     return replaceInstUsesWith(I, V);
 
   if (Value *V = SimplifyMulInst(Op0, Op1, SQ.getWithInstruction(&I)))