APFloat: Add isSmallestNormalized predicate function

[arsenm]

Summary

It was annoying to write the check for this in the one case I added,
and I'm planning on adding another, so add a convenient PatternMatch
like for other special case values.

I have no idea what is going on in the DoubleAPFloat case, I reversed
this from the makeSmallestNormalized test. Also could implement this
as *this == getSmallestNormalized() for less code, but this avoids the
construction of a temporary APFloat copy and follows the style of the
other functions.

[sepavloff]

llvm/include/llvm/ADT/APFloat.h

396

Returns *true* if...

llvm/lib/Support/APFloat.cpp

5022–5026

What prevents from using the same technique as in isSmallest? It looks more readable.

[arsenm]

Simplify DoubleFloat case

[arsenm]

Split out PatternMatch part

[arsenm]

Really move the patternmatch part

[sepavloff]

llvm/unittests/ADT/APFloatTest.cpp

695

Could you please also specify the numbers explicitly as float/double? I mean tests like:

EXPECT_TRUE(APFloat(0x1.0p-126F).isSmallestNormalized());

and similar check for double?

[arsenm]

Also check parsed strings in getSmallestNormalized

[sepavloff]

LGTM.

[arsenm]

191c1d95e880227a13687c77c940f63baf88c594

llvm/include/llvm/ADT/APFloat.h

public:
   bool isFiniteNonZero() const { return isFinite() && !isZero(); }
   bool isPosZero() const { return isZero() && !isNegative(); }
   bool isNegZero() const { return isZero() && isNegative(); }
 
   /// Returns true if and only if the number has the smallest possible non-zero
   /// magnitude in the current semantics.
   bool isSmallest() const;
 
+  /// Returns true if this is the smallest (by magnitude) normalized finite
+  /// number in the given semantics.
+  bool isSmallestNormalized() const;
+
   /// Returns true if and only if the number has the largest possible finite
   /// magnitude in the current semantics.
   bool isLargest() const;
 
   /// Returns true if and only if the number is an exact integer.
   bool isInteger() const;
 
   /// @}
private:
   unsigned int significandLSB() const;
   unsigned int significandMSB() const;
   void zeroSignificand();
   /// Return true if the significand excluding the integral bit is all ones.
   bool isSignificandAllOnes() const;
   bool isSignificandAllOnesExceptLSB() const;
   /// Return true if the significand excluding the integral bit is all zeros.
   bool isSignificandAllZeros() const;
+  bool isSignificandAllZerosExceptMSB() const;
 
   /// @}
 
   /// \name Arithmetic on special values.
   /// @{
 
   opStatus addOrSubtractSpecials(const IEEEFloat &, bool subtract);
   opStatus divideSpecials(const IEEEFloat &);
public:
   opStatus convertFromZeroExtendedInteger(const integerPart *Input,
                                           unsigned int InputSize, bool IsSigned,
                                           roundingMode RM);
   unsigned int convertToHexString(char *DST, unsigned int HexDigits,
                                   bool UpperCase, roundingMode RM) const;
 
   bool isDenormal() const;
   bool isSmallest() const;
+  bool isSmallestNormalized() const;
   bool isLargest() const;
   bool isInteger() const;
 
   void toString(SmallVectorImpl<char> &Str, unsigned FormatPrecision,
                 unsigned FormatMaxPadding, bool TruncateZero = true) const;
 
   bool getExactInverse(APFloat *inv) const;
 
public:
   bool isNegZero() const { return isZero() && isNegative(); }
   bool isPosInfinity() const { return isInfinity() && !isNegative(); }
   bool isNegInfinity() const { return isInfinity() && isNegative(); }
   bool isSmallest() const { APFLOAT_DISPATCH_ON_SEMANTICS(isSmallest()); }
   bool isLargest() const { APFLOAT_DISPATCH_ON_SEMANTICS(isLargest()); }
   bool isInteger() const { APFLOAT_DISPATCH_ON_SEMANTICS(isInteger()); }
   bool isIEEE() const { return usesLayout<IEEEFloat>(getSemantics()); }
 
+  bool isSmallestNormalized() const {
+    APFLOAT_DISPATCH_ON_SEMANTICS(isSmallestNormalized());
+  }
+
   APFloat &operator=(const APFloat &RHS) = default;
   APFloat &operator=(APFloat &&RHS) = default;
 
   void toString(SmallVectorImpl<char> &Str, unsigned FormatPrecision = 0,
                 unsigned FormatMaxPadding = 3, bool TruncateZero = true) const {
     APFLOAT_DISPATCH_ON_SEMANTICS(
         toString(Str, FormatPrecision, FormatMaxPadding, TruncateZero));
   }

llvm/lib/Support/APFloat.cpp

 bool IEEEFloat::isSmallest() const {
   // The smallest number by magnitude in our format will be the smallest
   // denormal, i.e. the floating point number with exponent being minimum
   // exponent and significand bitwise equal to 1 (i.e. with MSB equal to 0).
   return isFiniteNonZero() && exponent == semantics->minExponent &&
     significandMSB() == 0;
 }
 
+bool IEEEFloat::isSmallestNormalized() const {
+  return getCategory() == fcNormal && exponent == semantics->minExponent &&
+         isSignificandAllZerosExceptMSB();
+}
+
 bool IEEEFloat::isSignificandAllOnes() const {
   // Test if the significand excluding the integral bit is all ones. This allows
   // us to test for binade boundaries.
   const integerPart *Parts = significandParts();
   const unsigned PartCount = partCountForBits(semantics->precision);
   for (unsigned i = 0; i < PartCount - 1; i++)
     if (~Parts[i])
       return false;
bool IEEEFloat::isSignificandAllZeros() const {
   const integerPart HighBitMask = ~integerPart(0) >> NumHighBits;
 
   if (Parts[PartCount - 1] & HighBitMask)
     return false;
 
   return true;
 }
 
+bool IEEEFloat::isSignificandAllZerosExceptMSB() const {
+  const integerPart *Parts = significandParts();
+  const unsigned PartCount = partCountForBits(semantics->precision);
+
+  for (unsigned i = 0; i < PartCount - 1; i++) {
+    if (Parts[i])
+      return false;
+  }
+
+  const unsigned NumHighBits =
+      PartCount * integerPartWidth - semantics->precision + 1;
+  return Parts[PartCount - 1] == integerPart(1)
+                                     << (integerPartWidth - NumHighBits);
+}
+
 bool IEEEFloat::isLargest() const {
   if (semantics->nonFiniteBehavior == fltNonfiniteBehavior::NanOnly) {
     // The largest number by magnitude in our format will be the floating point
     // number with maximum exponent and with significand that is all ones except
     // the LSB.
     return isFiniteNonZero() && exponent == semantics->maxExponent &&
            isSignificandAllOnesExceptLSB();
   } else {

 bool DoubleAPFloat::isSmallest() const {
   if (getCategory() != fcNormal)
     return false;
   DoubleAPFloat Tmp(*this);
   Tmp.makeSmallest(this->isNegative());
   return Tmp.compare(*this) == cmpEqual;
 }
 
+bool DoubleAPFloat::isSmallestNormalized() const {
+  if (getCategory() != fcNormal)
+    return false;
+
+  DoubleAPFloat Tmp(*this);
+  Tmp.makeSmallestNormalized(this->isNegative());
+  return Tmp.compare(*this) == cmpEqual;
+}
+
 bool DoubleAPFloat::isLargest() const {
   if (getCategory() != fcNormal)
     return false;
   DoubleAPFloat Tmp(*this);
   Tmp.makeLargest(this->isNegative());
   return Tmp.compare(*this) == cmpEqual;
 }
 

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

static Instruction *foldFabsWithFcmpZero(FCmpInst &I, InstCombinerImpl &IC) {
   if (!match(I.getOperand(0), m_FAbs(m_Value(X))))
     return nullptr;
 
   const APFloat *C;
   if (!match(I.getOperand(1), m_APFloat(C)))
     return nullptr;
 
   if (!C->isPosZero()) {
-    if (*C != APFloat::getSmallestNormalized(C->getSemantics()))
+    if (!C->isSmallestNormalized())
       return nullptr;
 
     const Function *F = I.getFunction();
     DenormalMode Mode = F->getDenormalMode(C->getSemantics());
     if (Mode.Input == DenormalMode::PreserveSign ||
         Mode.Input == DenormalMode::PositiveZero) {
 
       auto replaceFCmp = [](FCmpInst *I, FCmpInst::Predicate P, Value *X) {

llvm/unittests/ADT/APFloatTest.cpp

// Test quadruple precision
 
     APFloat Val2(APFloat::IEEEquad(), 2);
     APFloat T(APFloat::IEEEquad(), MinNormalStr);
     T.divide(Val2, rdmd);
     EXPECT_TRUE(T.isDenormal());
   }
 }
 
+TEST(APFloatTest, IsSmallestNormalized) {
+  for (unsigned I = 0; I != APFloat::S_MaxSemantics + 1; ++I) {
+    const fltSemantics &Semantics =
+        APFloat::EnumToSemantics(static_cast<APFloat::Semantics>(I));
+
+    EXPECT_FALSE(APFloat::getZero(Semantics, false).isSmallestNormalized());
+    EXPECT_FALSE(APFloat::getZero(Semantics, true).isSmallestNormalized());
+
+    EXPECT_FALSE(APFloat::getInf(Semantics, false).isSmallestNormalized());
+    EXPECT_FALSE(APFloat::getInf(Semantics, true).isSmallestNormalized());
+
+    EXPECT_FALSE(APFloat::getQNaN(Semantics).isSmallestNormalized());
+    EXPECT_FALSE(APFloat::getSNaN(Semantics).isSmallestNormalized());
+
+    EXPECT_FALSE(APFloat::getLargest(Semantics).isSmallestNormalized());
+    EXPECT_FALSE(APFloat::getLargest(Semantics, true).isSmallestNormalized());
+
+    EXPECT_FALSE(APFloat::getSmallest(Semantics).isSmallestNormalized());
+    EXPECT_FALSE(APFloat::getSmallest(Semantics, true).isSmallestNormalized());
+
+    EXPECT_FALSE(APFloat::getAllOnesValue(Semantics).isSmallestNormalized());
+
+    APFloat PosSmallestNormalized =
+        APFloat::getSmallestNormalized(Semantics, false);
+    APFloat NegSmallestNormalized =
+        APFloat::getSmallestNormalized(Semantics, true);
+    EXPECT_TRUE(PosSmallestNormalized.isSmallestNormalized());
+    EXPECT_TRUE(NegSmallestNormalized.isSmallestNormalized());
+
+    for (APFloat *Val : {&PosSmallestNormalized, &NegSmallestNormalized}) {
+      bool OldSign = Val->isNegative();
+
+      // Step down, make sure it's still not smallest normalized.
+      EXPECT_EQ(APFloat::opOK, Val->next(false));
+      EXPECT_EQ(OldSign, Val->isNegative());
+      EXPECT_FALSE(Val->isSmallestNormalized());
+      EXPECT_EQ(OldSign, Val->isNegative());
+
+      // Step back up should restore it to being smallest normalized.
+      EXPECT_EQ(APFloat::opOK, Val->next(true));
+      EXPECT_TRUE(Val->isSmallestNormalized());
+      EXPECT_EQ(OldSign, Val->isNegative());
+
+      // Step beyond should no longer smallest normalized.
+      EXPECT_EQ(APFloat::opOK, Val->next(true));
+      EXPECT_FALSE(Val->isSmallestNormalized());
+      EXPECT_EQ(OldSign, Val->isNegative());
+    }
+  }
+}
+
 TEST(APFloatTest, Zero) {
   EXPECT_EQ(0.0f,  APFloat(0.0f).convertToFloat());
   EXPECT_EQ(-0.0f, APFloat(-0.0f).convertToFloat());
   EXPECT_TRUE(APFloat(-0.0f).isNegative());
 
   EXPECT_EQ(0.0,  APFloat(0.0).convertToDouble());
   EXPECT_EQ(-0.0, APFloat(-0.0).convertToDouble());
   EXPECT_TRUE(APFloat(-0.0).isNegative());