ConstRange: factor and introduce splitPosNeg (NFC) (llvm#126528)

Factor out some code that splits a ConstantRange into positive and
negative components, introducing ConstantRange::splitPosNeg.

Author: artagnon

llvm/include/llvm/IR/ConstantRange.h

@@ -92,6 +92,10 @@ class [[nodiscard]] ConstantRange {
   /// unsigned domain.
   static ConstantRange fromKnownBits(const KnownBits &Known, bool IsSigned);
 
+  /// Split the ConstantRange into positive and negative components, ignoring
+  /// zero values.
+  std::pair<ConstantRange, ConstantRange> splitPosNeg() const;
+
   /// Produce the smallest range such that all values that may satisfy the given
   /// predicate with any value contained within Other is contained in the
   /// returned range.  Formally, this returns a superset of

llvm/lib/IR/ConstantRange.cpp

@@ -95,6 +95,17 @@ KnownBits ConstantRange::toKnownBits() const {
   return Known;
 }
 
+std::pair<ConstantRange, ConstantRange> ConstantRange::splitPosNeg() const {
+  uint32_t BW = getBitWidth();
+  APInt Zero = APInt::getZero(BW), One = APInt(BW, 1);
+  APInt SignedMin = APInt::getSignedMinValue(BW);
+  // There are no positive 1-bit values. The 1 would get interpreted as -1.
+  ConstantRange PosFilter =
+      BW == 1 ? getEmpty() : ConstantRange(One, SignedMin);
+  ConstantRange NegFilter(SignedMin, Zero);
+  return {intersectWith(PosFilter), intersectWith(NegFilter)};
+}
+
 ConstantRange ConstantRange::makeAllowedICmpRegion(CmpInst::Predicate Pred,
                                                    const ConstantRange &CR) {
   if (CR.isEmptySet())
@@ -1356,20 +1367,14 @@ ConstantRange::udiv(const ConstantRange &RHS) const {
 }
 
 ConstantRange ConstantRange::sdiv(const ConstantRange &RHS) const {
+  APInt Zero = APInt::getZero(getBitWidth());
+  APInt SignedMin = APInt::getSignedMinValue(getBitWidth());
+
   // We split up the LHS and RHS into positive and negative components
   // and then also compute the positive and negative components of the result
   // separately by combining division results with the appropriate signs.
-  APInt Zero = APInt::getZero(getBitWidth());
-  APInt SignedMin = APInt::getSignedMinValue(getBitWidth());
-  // There are no positive 1-bit values. The 1 would get interpreted as -1.
-  ConstantRange PosFilter =
-      getBitWidth() == 1 ? getEmpty()
-                         : ConstantRange(APInt(getBitWidth(), 1), SignedMin);
-  ConstantRange NegFilter(SignedMin, Zero);
-  ConstantRange PosL = intersectWith(PosFilter);
-  ConstantRange NegL = intersectWith(NegFilter);
-  ConstantRange PosR = RHS.intersectWith(PosFilter);
-  ConstantRange NegR = RHS.intersectWith(NegFilter);
+  auto [PosL, NegL] = splitPosNeg();
+  auto [PosR, NegR] = RHS.splitPosNeg();
 
   ConstantRange PosRes = getEmpty();
   if (!PosL.isEmptySet() && !PosR.isEmptySet())

llvm/unittests/IR/ConstantRangeTest.cpp

@@ -2126,6 +2126,16 @@ TEST(ConstantRange, GetEquivalentICmp) {
   });
 }
 
+TEST(ConstantRange, SplitPosNeg) {
+  EnumerateInterestingConstantRanges([](const ConstantRange &CR) {
+    auto [Pos, Neg] = CR.splitPosNeg();
+    EXPECT_TRUE(Pos.isAllPositive());
+    EXPECT_TRUE(Neg.isAllNegative());
+    if (CR.getBitWidth() == 1)
+      EXPECT_TRUE(Pos.isEmptySet());
+  });
+}
+
 #define EXPECT_MAY_OVERFLOW(op) \
   EXPECT_EQ(ConstantRange::OverflowResult::MayOverflow, (op))
 #define EXPECT_ALWAYS_OVERFLOWS_LOW(op) \