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

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

Author: Ramkumar Ramachandra (artagnon)

<details>
<summary>Changes</summary>

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

---
Full diff: https://github.com/llvm/llvm-project/pull/126528.diff


2 Files Affected:

- (modified) llvm/include/llvm/IR/ConstantRange.h (+3) 
- (modified) llvm/lib/IR/ConstantRange.cpp (+16-11) 


``````````diff
diff --git a/llvm/include/llvm/IR/ConstantRange.h b/llvm/include/llvm/IR/ConstantRange.h
index d086c25390fd22..82af38fcd0b7c4 100644
--- a/llvm/include/llvm/IR/ConstantRange.h
+++ b/llvm/include/llvm/IR/ConstantRange.h
@@ -92,6 +92,9 @@ class [[nodiscard]] ConstantRange {
   /// unsigned domain.
   static ConstantRange fromKnownBits(const KnownBits &Known, bool IsSigned);
 
+  /// Split the ConstantRange into positive and negative components.
+  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
diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 35664353989929..d04eb81eed05c7 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/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);
+  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(APInt(BW, 1), 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())

``````````

</details>


https://github.com/llvm/llvm-project/pull/126528