[LLVM][IR] Add constant range support for floating-point types (#86483)

This patch adds basic constant range support for floating-point types to enable range-based optimizations.

Author: dtcxzyw

llvm/include/llvm/ADT/APFloat.h

@@ -1534,6 +1534,11 @@ inline APFloat maximumnum(const APFloat &A, const APFloat &B) {
   return A < B ? B : A;
 }
 
+inline raw_ostream &operator<<(raw_ostream &OS, const APFloat &V) {
+  V.print(OS);
+  return OS;
+}
+
 // We want the following functions to be available in the header for inlining.
 // We cannot define them inline in the class definition of `DoubleAPFloat`
 // because doing so would instantiate `std::unique_ptr<APFloat[]>` before

llvm/include/llvm/IR/ConstantFPRange.h

@@ -0,0 +1,204 @@
+//===- ConstantFPRange.h - Represent a range for floating-point -*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Represent a range of possible values that may occur when the program is run
+// for a floating-point value. This keeps track of a lower and upper bound for
+// the constant.
+//
+// Range = [Lower, Upper] U (MayBeQNaN ? QNaN : {}) U (MayBeSNaN ? SNaN : {})
+// Specifically, [inf, -inf] represents an empty set.
+// Note:
+// 1. Bounds are inclusive.
+// 2. -0 is considered to be less than 0. That is, range [0, 0] doesn't contain
+// -0.
+// 3. Currently wrapping ranges are not supported.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_IR_CONSTANTFPRANGE_H
+#define LLVM_IR_CONSTANTFPRANGE_H
+
+#include "llvm/ADT/APFloat.h"
+#include "llvm/IR/Instructions.h"
+#include <optional>
+
+namespace llvm {
+
+class raw_ostream;
+struct KnownFPClass;
+
+/// This class represents a range of floating-point values.
+class [[nodiscard]] ConstantFPRange {
+  APFloat Lower, Upper;
+  bool MayBeQNaN : 1;
+  bool MayBeSNaN : 1;
+
+  /// Create empty constant range with same semantics.
+  ConstantFPRange getEmpty() const {
+    return ConstantFPRange(getSemantics(), /*IsFullSet=*/false);
+  }
+
+  /// Create full constant range with same semantics.
+  ConstantFPRange getFull() const {
+    return ConstantFPRange(getSemantics(), /*IsFullSet=*/true);
+  }
+
+  void makeEmpty();
+  void makeFull();
+  bool isNaNOnly() const;
+
+  /// Initialize a full or empty set for the specified semantics.
+  explicit ConstantFPRange(const fltSemantics &Sem, bool IsFullSet);
+
+public:
+  /// Initialize a range to hold the single specified value.
+  explicit ConstantFPRange(const APFloat &Value);
+
+  /// Initialize a range of values explicitly.
+  /// Note: If \p LowerVal is greater than \p UpperVal, please use the canonical
+  /// form [Inf, -Inf].
+  ConstantFPRange(APFloat LowerVal, APFloat UpperVal, bool MayBeQNaN,
+                  bool MayBeSNaN);
+
+  /// Create empty constant range with the given semantics.
+  static ConstantFPRange getEmpty(const fltSemantics &Sem) {
+    return ConstantFPRange(Sem, /*IsFullSet=*/false);
+  }
+
+  /// Create full constant range with the given semantics.
+  static ConstantFPRange getFull(const fltSemantics &Sem) {
+    return ConstantFPRange(Sem, /*IsFullSet=*/true);
+  }
+
+  /// Helper for (-inf, inf) to represent all finite values.
+  static ConstantFPRange getFinite(const fltSemantics &Sem);
+
+  /// Create a range which doesn't contain NaNs.
+  static ConstantFPRange getNonNaN(APFloat LowerVal, APFloat UpperVal) {
+    return ConstantFPRange(std::move(LowerVal), std::move(UpperVal),
+                           /*MayBeQNaN=*/false, /*MayBeSNaN=*/false);
+  }
+
+  /// Create a range which may contain NaNs.
+  static ConstantFPRange getMayBeNaN(APFloat LowerVal, APFloat UpperVal) {
+    return ConstantFPRange(std::move(LowerVal), std::move(UpperVal),
+                           /*MayBeQNaN=*/true, /*MayBeSNaN=*/true);
+  }
+
+  /// Create a range which only contains NaNs.
+  static ConstantFPRange getNaNOnly(const fltSemantics &Sem, bool MayBeQNaN,
+                                    bool MayBeSNaN);
+
+  /// 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
+  /// 'union over all y in Other . { x : fcmp op x y is true }'.  If the exact
+  /// answer is not representable as a ConstantFPRange, the return value will be
+  /// a proper superset of the above.
+  ///
+  /// Example: Pred = ole and Other = float [2, 5] returns Result = [-inf, 5]
+  static ConstantFPRange makeAllowedFCmpRegion(FCmpInst::Predicate Pred,
+                                               const ConstantFPRange &Other);
+
+  /// Produce the largest range such that all values in the returned range
+  /// satisfy the given predicate with all values contained within Other.
+  /// Formally, this returns a subset of
+  /// 'intersection over all y in Other . { x : fcmp op x y is true }'.  If the
+  /// exact answer is not representable as a ConstantFPRange, the return value
+  /// will be a proper subset of the above.
+  ///
+  /// Example: Pred = ole and Other = float [2, 5] returns [-inf, 2]
+  static ConstantFPRange makeSatisfyingFCmpRegion(FCmpInst::Predicate Pred,
+                                                  const ConstantFPRange &Other);
+
+  /// Produce the exact range such that all values in the returned range satisfy
+  /// the given predicate with any value contained within Other. Formally, this
+  /// returns the exact answer when the superset of 'union over all y in Other
+  /// is exactly same as the subset of intersection over all y in Other.
+  /// { x : fcmp op x y is true}'.
+  ///
+  /// Example: Pred = olt and Other = float 3 returns [-inf, 3)
+  static ConstantFPRange makeExactFCmpRegion(FCmpInst::Predicate Pred,
+                                             const APFloat &Other);
+
+  /// Does the predicate \p Pred hold between ranges this and \p Other?
+  /// NOTE: false does not mean that inverse predicate holds!
+  bool fcmp(FCmpInst::Predicate Pred, const ConstantFPRange &Other) const;
+
+  /// Return the lower value for this range.
+  const APFloat &getLower() const { return Lower; }
+
+  /// Return the upper value for this range.
+  const APFloat &getUpper() const { return Upper; }
+
+  bool containsNaN() const { return MayBeQNaN || MayBeSNaN; }
+  bool containsQNaN() const { return MayBeQNaN; }
+  bool containsSNaN() const { return MayBeSNaN; }
+
+  /// Get the semantics of this ConstantFPRange.
+  const fltSemantics &getSemantics() const { return Lower.getSemantics(); }
+
+  /// Return true if this set contains all of the elements possible
+  /// for this data-type.
+  bool isFullSet() const;
+
+  /// Return true if this set contains no members.
+  bool isEmptySet() const;
+
+  /// Return true if the specified value is in the set.
+  bool contains(const APFloat &Val) const;
+
+  /// Return true if the other range is a subset of this one.
+  bool contains(const ConstantFPRange &CR) const;
+
+  /// If this set contains a single element, return it, otherwise return null.
+  const APFloat *getSingleElement() const;
+
+  /// Return true if this set contains exactly one member.
+  bool isSingleElement() const { return getSingleElement() != nullptr; }
+
+  /// Return true if the sign bit of all values in this range is 1.
+  /// Return false if the sign bit of all values in this range is 0.
+  /// Otherwise, return std::nullopt.
+  std::optional<bool> getSignBit() const;
+
+  /// Return true if this range is equal to another range.
+  bool operator==(const ConstantFPRange &CR) const;
+  /// Return true if this range is not equal to another range.
+  bool operator!=(const ConstantFPRange &CR) const { return !operator==(CR); }
+
+  /// Return the FPClassTest which will return true for the value.
+  FPClassTest classify() const;
+
+  /// Return known floating-point classes for values in this range.
+  KnownFPClass toKnownFPClass() const;
+
+  /// Print out the bounds to a stream.
+  void print(raw_ostream &OS) const;
+
+  /// Allow printing from a debugger easily.
+  void dump() const;
+
+  /// Return the range that results from the intersection of this range with
+  /// another range.
+  ConstantFPRange intersectWith(const ConstantFPRange &CR) const;
+
+  /// Return the range that results from the union of this range
+  /// with another range.  The resultant range is guaranteed to include the
+  /// elements of both sets, but may contain more.
+  ConstantFPRange unionWith(const ConstantFPRange &CR) const;
+};
+
+inline raw_ostream &operator<<(raw_ostream &OS, const ConstantFPRange &CR) {
+  CR.print(OS);
+  return OS;
+}
+
+} // end namespace llvm
+
+#endif // LLVM_IR_CONSTANTFPRANGE_H

llvm/lib/IR/CMakeLists.txt

@@ -8,6 +8,7 @@ add_llvm_component_library(LLVMCore
   BuiltinGCs.cpp
   Comdat.cpp
   ConstantFold.cpp
+  ConstantFPRange.cpp
   ConstantRange.cpp
   ConstantRangeList.cpp
   Constants.cpp