[ValueTracking] Merge cannotBeOrderedLessThanZeroImpl into computeKnownFPClass (#76360)

This patch merges the logic of `cannotBeOrderedLessThanZeroImpl` into
`computeKnownFPClass` to improve the signbit inference.

---------

Co-authored-by: Matt Arsenault <[email protected]>

Author: dtcxzyw

llvm/include/llvm/Analysis/ValueTracking.h

@@ -358,6 +358,12 @@ struct KnownFPClass {
 
   void knownNot(FPClassTest RuleOut) {
     KnownFPClasses = KnownFPClasses & ~RuleOut;
+    if (isKnownNever(fcNan) && !SignBit) {
+      if (isKnownNever(fcNegative))
+        SignBit = false;
+      else if (isKnownNever(fcPositive))
+        SignBit = true;
+    }
   }
 
   void fneg() {
@@ -393,6 +399,12 @@ struct KnownFPClass {
     SignBit = false;
   }
 
+  /// Assume the sign bit is one.
+  void signBitMustBeOne() {
+    KnownFPClasses &= (fcNegative | fcNan);
+    SignBit = true;
+  }
+
   void copysign(const KnownFPClass &Sign) {
     // Don't know anything about the sign of the source. Expand the possible set
     // to its opposite sign pair.
@@ -579,15 +591,18 @@ inline bool isKnownNeverNaN(const Value *V, const DataLayout &DL,
   return Known.isKnownNeverNaN();
 }
 
-/// Return true if we can prove that the specified FP value's sign bit is 0.
-///
-///      NaN --> true/false (depending on the NaN's sign bit)
-///       +0 --> true
-///       -0 --> false
-///   x > +0 --> true
-///   x < -0 --> false
-bool SignBitMustBeZero(const Value *V, const DataLayout &DL,
-                       const TargetLibraryInfo *TLI);
+/// Return false if we can prove that the specified FP value's sign bit is 0.
+/// Return true if we can prove that the specified FP value's sign bit is 1.
+/// Otherwise return std::nullopt.
+inline std::optional<bool> computeKnownFPSignBit(
+    const Value *V, const DataLayout &DL,
+    const TargetLibraryInfo *TLI = nullptr, unsigned Depth = 0,
+    AssumptionCache *AC = nullptr, const Instruction *CtxI = nullptr,
+    const DominatorTree *DT = nullptr, bool UseInstrInfo = true) {
+  KnownFPClass Known = computeKnownFPClass(V, DL, fcAllFlags, Depth, TLI, AC,
+                                           CtxI, DT, UseInstrInfo);
+  return Known.SignBit;
+}
 
 /// If the specified value can be set by repeating the same byte in memory,
 /// return the i8 value that it is represented with. This is true for all i8

llvm/lib/Analysis/InstructionSimplify.cpp

@@ -5762,9 +5762,9 @@ static Value *simplifyFMAFMul(Value *Op0, Value *Op1, FastMathFlags FMF,
       return ConstantFP::getZero(Op0->getType());
 
     // +normal number * (-)0.0 --> (-)0.0
-    if (isKnownNeverInfOrNaN(Op0, Q.DL, Q.TLI, 0, Q.AC, Q.CxtI, Q.DT) &&
-        // TODO: Check SignBit from computeKnownFPClass when it's more complete.
-        SignBitMustBeZero(Op0, Q.DL, Q.TLI))
+    KnownFPClass Known = computeKnownFPClass(
+        Op0, FMF, Q.DL, fcInf | fcNan, /*Depth=*/0, Q.TLI, Q.AC, Q.CxtI, Q.DT);
+    if (Known.SignBit == false && Known.isKnownNever(fcInf | fcNan))
       return Op1;
   }
 
@@ -6217,7 +6217,8 @@ static Value *simplifyUnaryIntrinsic(Function *F, Value *Op0,
   Value *X;
   switch (IID) {
   case Intrinsic::fabs:
-    if (SignBitMustBeZero(Op0, Q.DL, Q.TLI))
+    if (computeKnownFPSignBit(Op0, Q.DL, Q.TLI, /*Depth=*/0, Q.AC, Q.CxtI,
+                              Q.DT) == false)
       return Op0;
     break;
   case Intrinsic::bswap:

llvm/lib/Analysis/ValueTracking.cpp

@@ -3706,205 +3706,6 @@ Intrinsic::ID llvm::getIntrinsicForCallSite(const CallBase &CB,
   return Intrinsic::not_intrinsic;
 }
 
-/// Deprecated, use computeKnownFPClass instead.
-///
-/// If \p SignBitOnly is true, test for a known 0 sign bit rather than a
-/// standard ordered compare. e.g. make -0.0 olt 0.0 be true because of the sign
-/// bit despite comparing equal.
-static bool cannotBeOrderedLessThanZeroImpl(const Value *V,
-                                            const DataLayout &DL,
-                                            const TargetLibraryInfo *TLI,
-                                            bool SignBitOnly, unsigned Depth) {
-  // TODO: This function does not do the right thing when SignBitOnly is true
-  // and we're lowering to a hypothetical IEEE 754-compliant-but-evil platform
-  // which flips the sign bits of NaNs.  See
-  // https://llvm.org/bugs/show_bug.cgi?id=31702.
-
-  if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
-    return !CFP->getValueAPF().isNegative() ||
-           (!SignBitOnly && CFP->getValueAPF().isZero());
-  }
-
-  // Handle vector of constants.
-  if (auto *CV = dyn_cast<Constant>(V)) {
-    if (auto *CVFVTy = dyn_cast<FixedVectorType>(CV->getType())) {
-      unsigned NumElts = CVFVTy->getNumElements();
-      for (unsigned i = 0; i != NumElts; ++i) {
-        auto *CFP = dyn_cast_or_null<ConstantFP>(CV->getAggregateElement(i));
-        if (!CFP)
-          return false;
-        if (CFP->getValueAPF().isNegative() &&
-            (SignBitOnly || !CFP->getValueAPF().isZero()))
-          return false;
-      }
-
-      // All non-negative ConstantFPs.
-      return true;
-    }
-  }
-
-  if (Depth == MaxAnalysisRecursionDepth)
-    return false;
-
-  const Operator *I = dyn_cast<Operator>(V);
-  if (!I)
-    return false;
-
-  switch (I->getOpcode()) {
-  default:
-    break;
-  // Unsigned integers are always nonnegative.
-  case Instruction::UIToFP:
-    return true;
-  case Instruction::FDiv:
-    // X / X is always exactly 1.0 or a NaN.
-    if (I->getOperand(0) == I->getOperand(1) &&
-        (!SignBitOnly || cast<FPMathOperator>(I)->hasNoNaNs()))
-      return true;
-
-    // Set SignBitOnly for RHS, because X / -0.0 is -Inf (or NaN).
-    return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), DL, TLI,
-                                           SignBitOnly, Depth + 1) &&
-           cannotBeOrderedLessThanZeroImpl(I->getOperand(1), DL, TLI,
-                                           /*SignBitOnly*/ true, Depth + 1);
-  case Instruction::FMul:
-    // X * X is always non-negative or a NaN.
-    if (I->getOperand(0) == I->getOperand(1) &&
-        (!SignBitOnly || cast<FPMathOperator>(I)->hasNoNaNs()))
-      return true;
-
-    [[fallthrough]];
-  case Instruction::FAdd:
-  case Instruction::FRem:
-    return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), DL, TLI,
-                                           SignBitOnly, Depth + 1) &&
-           cannotBeOrderedLessThanZeroImpl(I->getOperand(1), DL, TLI,
-                                           SignBitOnly, Depth + 1);
-  case Instruction::Select:
-    return cannotBeOrderedLessThanZeroImpl(I->getOperand(1), DL, TLI,
-                                           SignBitOnly, Depth + 1) &&
-           cannotBeOrderedLessThanZeroImpl(I->getOperand(2), DL, TLI,
-                                           SignBitOnly, Depth + 1);
-  case Instruction::FPExt:
-  case Instruction::FPTrunc:
-    // Widening/narrowing never change sign.
-    return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), DL, TLI,
-                                           SignBitOnly, Depth + 1);
-  case Instruction::ExtractElement:
-    // Look through extract element. At the moment we keep this simple and skip
-    // tracking the specific element. But at least we might find information
-    // valid for all elements of the vector.
-    return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), DL, TLI,
-                                           SignBitOnly, Depth + 1);
-  case Instruction::Call:
-    const auto *CI = cast<CallInst>(I);
-    Intrinsic::ID IID = getIntrinsicForCallSite(*CI, TLI);
-    switch (IID) {
-    default:
-      break;
-    case Intrinsic::canonicalize:
-    case Intrinsic::arithmetic_fence:
-    case Intrinsic::floor:
-    case Intrinsic::ceil:
-    case Intrinsic::trunc:
-    case Intrinsic::rint:
-    case Intrinsic::nearbyint:
-    case Intrinsic::round:
-    case Intrinsic::roundeven:
-    case Intrinsic::fptrunc_round:
-      return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), DL, TLI,
-                                             SignBitOnly, Depth + 1);
-    case Intrinsic::maxnum: {
-      Value *V0 = I->getOperand(0), *V1 = I->getOperand(1);
-      auto isPositiveNum = [&](Value *V) {
-        if (SignBitOnly) {
-          // With SignBitOnly, this is tricky because the result of
-          // maxnum(+0.0, -0.0) is unspecified. Just check if the operand is
-          // a constant strictly greater than 0.0.
-          const APFloat *C;
-          return match(V, m_APFloat(C)) &&
-                 *C > APFloat::getZero(C->getSemantics());
-        }
-
-        // -0.0 compares equal to 0.0, so if this operand is at least -0.0,
-        // maxnum can't be ordered-less-than-zero.
-        return isKnownNeverNaN(V, DL, TLI) &&
-               cannotBeOrderedLessThanZeroImpl(V, DL, TLI, false, Depth + 1);
-      };
-
-      // TODO: This could be improved. We could also check that neither operand
-      //       has its sign bit set (and at least 1 is not-NAN?).
-      return isPositiveNum(V0) || isPositiveNum(V1);
-    }
-
-    case Intrinsic::maximum:
-      return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), DL, TLI,
-                                             SignBitOnly, Depth + 1) ||
-             cannotBeOrderedLessThanZeroImpl(I->getOperand(1), DL, TLI,
-                                             SignBitOnly, Depth + 1);
-    case Intrinsic::minnum:
-    case Intrinsic::minimum:
-      return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), DL, TLI,
-                                             SignBitOnly, Depth + 1) &&
-             cannotBeOrderedLessThanZeroImpl(I->getOperand(1), DL, TLI,
-                                             SignBitOnly, Depth + 1);
-    case Intrinsic::exp:
-    case Intrinsic::exp2:
-    case Intrinsic::fabs:
-      return true;
-    case Intrinsic::copysign:
-      // Only the sign operand matters.
-      return cannotBeOrderedLessThanZeroImpl(I->getOperand(1), DL, TLI, true,
-                                             Depth + 1);
-    case Intrinsic::sqrt:
-      // sqrt(x) is always >= -0 or NaN.  Moreover, sqrt(x) == -0 iff x == -0.
-      if (!SignBitOnly)
-        return true;
-      return CI->hasNoNaNs() &&
-             (CI->hasNoSignedZeros() ||
-              cannotBeNegativeZero(CI->getOperand(0), DL, TLI));
-
-    case Intrinsic::powi:
-      if (ConstantInt *Exponent = dyn_cast<ConstantInt>(I->getOperand(1))) {
-        // powi(x,n) is non-negative if n is even.
-        if (Exponent->getBitWidth() <= 64 && Exponent->getSExtValue() % 2u == 0)
-          return true;
-      }
-      // TODO: This is not correct.  Given that exp is an integer, here are the
-      // ways that pow can return a negative value:
-      //
-      //   pow(x, exp)    --> negative if exp is odd and x is negative.
-      //   pow(-0, exp)   --> -inf if exp is negative odd.
-      //   pow(-0, exp)   --> -0 if exp is positive odd.
-      //   pow(-inf, exp) --> -0 if exp is negative odd.
-      //   pow(-inf, exp) --> -inf if exp is positive odd.
-      //
-      // Therefore, if !SignBitOnly, we can return true if x >= +0 or x is NaN,
-      // but we must return false if x == -0.  Unfortunately we do not currently
-      // have a way of expressing this constraint.  See details in
-      // https://llvm.org/bugs/show_bug.cgi?id=31702.
-      return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), DL, TLI,
-                                             SignBitOnly, Depth + 1);
-
-    case Intrinsic::fma:
-    case Intrinsic::fmuladd:
-      // x*x+y is non-negative if y is non-negative.
-      return I->getOperand(0) == I->getOperand(1) &&
-             (!SignBitOnly || cast<FPMathOperator>(I)->hasNoNaNs()) &&
-             cannotBeOrderedLessThanZeroImpl(I->getOperand(2), DL, TLI,
-                                             SignBitOnly, Depth + 1);
-    }
-    break;
-  }
-  return false;
-}
-
-bool llvm::SignBitMustBeZero(const Value *V, const DataLayout &DL,
-                             const TargetLibraryInfo *TLI) {
-  // FIXME: Use computeKnownFPClass and pass all arguments
-  return cannotBeOrderedLessThanZeroImpl(V, DL, TLI, true, 0);
-}
-
 /// Return true if it's possible to assume IEEE treatment of input denormals in
 /// \p F for \p Val.
 static bool inputDenormalIsIEEE(const Function &F, const Type *Ty) {
@@ -4489,7 +4290,6 @@ static void computeKnownFPClassForFPTrunc(const Operator *Op,
   // Infinity needs a range check.
 }
 
-// TODO: Merge implementation of cannotBeOrderedLessThanZero into here.
 void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
                          FPClassTest InterestedClasses, KnownFPClass &Known,
                          unsigned Depth, const SimplifyQuery &Q) {
@@ -4514,6 +4314,8 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
   const Constant *CV = dyn_cast<Constant>(V);
   if (VFVTy && CV) {
     Known.KnownFPClasses = fcNone;
+    bool SignBitAllZero = true;
+    bool SignBitAllOne = true;
 
     // For vectors, verify that each element is not NaN.
     unsigned NumElts = VFVTy->getNumElements();
@@ -4531,10 +4333,15 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
         return;
       }
 
-      KnownFPClass KnownElt{CElt->getValueAPF().classify(), CElt->isNegative()};
-      Known |= KnownElt;
+      const APFloat &C = CElt->getValueAPF();
+      Known.KnownFPClasses |= C.classify();
+      if (C.isNegative())
+        SignBitAllZero = false;
+      else
+        SignBitAllOne = false;
     }
-
+    if (SignBitAllOne != SignBitAllZero)
+      Known.SignBit = SignBitAllOne;
     return;
   }
 
@@ -4673,7 +4480,6 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
       computeKnownFPClass(II->getArgOperand(2), DemandedElts, InterestedClasses,
                           KnownAddend, Depth + 1, Q);
 
-      // TODO: Known sign bit with no nans
       if (KnownAddend.cannotBeOrderedLessThanZero())
         Known.knownNot(fcNegative);
       break;
@@ -4707,7 +4513,7 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
           (F && KnownSrc.isKnownNeverLogicalNegZero(*F, II->getType()))) {
         Known.knownNot(fcNegZero);
         if (KnownSrc.isKnownNeverNaN())
-          Known.SignBit = false;
+          Known.signBitMustBeZero();
       }
 
       break;
@@ -4777,7 +4583,6 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
       // subtargets on AMDGPU the min/max instructions would not flush the
       // output and return the original value.
       //
-      // TODO: This could be refined based on the sign
       if ((Known.KnownFPClasses & fcZero) != fcNone &&
           !Known.isKnownNeverSubnormal()) {
         const Function *Parent = II->getFunction();
@@ -4790,6 +4595,26 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
           Known.KnownFPClasses |= fcZero;
       }
 
+      if (Known.isKnownNeverNaN()) {
+        if (KnownLHS.SignBit && KnownRHS.SignBit &&
+            *KnownLHS.SignBit == *KnownRHS.SignBit) {
+          if (*KnownLHS.SignBit)
+            Known.signBitMustBeOne();
+          else
+            Known.signBitMustBeZero();
+        } else if ((IID == Intrinsic::maximum || IID == Intrinsic::minimum) ||
+                   ((KnownLHS.isKnownNeverNegZero() ||
+                     KnownRHS.isKnownNeverPosZero()) &&
+                    (KnownLHS.isKnownNeverPosZero() ||
+                     KnownRHS.isKnownNeverNegZero()))) {
+          if ((IID == Intrinsic::maximum || IID == Intrinsic::maxnum) &&
+              (KnownLHS.SignBit == false || KnownRHS.SignBit == false))
+            Known.signBitMustBeZero();
+          else if ((IID == Intrinsic::minimum || IID == Intrinsic::minnum) &&
+                   (KnownLHS.SignBit == true || KnownRHS.SignBit == true))
+            Known.signBitMustBeOne();
+        }
+      }
       break;
     }
     case Intrinsic::canonicalize: {
@@ -4889,7 +4714,7 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
                           KnownSrc, Depth + 1, Q);
       if (KnownSrc.isKnownNeverNaN()) {
         Known.knownNot(fcNan);
-        Known.SignBit = false;
+        Known.signBitMustBeZero();
       }
 
       break;
@@ -5139,6 +4964,13 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
     if (!KnownLHS.isKnownNeverNaN())
       break;
 
+    if (KnownLHS.SignBit && KnownRHS.SignBit) {
+      if (*KnownLHS.SignBit == *KnownRHS.SignBit)
+        Known.signBitMustBeZero();
+      else
+        Known.signBitMustBeOne();
+    }
+
     // If 0 * +/-inf produces NaN.
     if (KnownLHS.isKnownNeverInfinity() && KnownRHS.isKnownNeverInfinity()) {
       Known.knownNot(fcNan);