[LLVM][IR] Add constant range support for floating-point types

[dtcxzyw]

Related issues: #68301 #70985 #82381

[github-actions]

✅ With the latest revision this PR passed the Python code formatter.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[dtcxzyw]

@tschuett This patch is not ready for review.

[tschuett]

Sorry. The GlobalIsel combiner already uses ConstantRange. I would like to use ConstantFPRange as well.

[tschuett]

llvm-project/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

Line 6760 in edcf65d

ConstantRange CR1 = ConstantRange::makeExactICmpRegion(

[llvmbot]

@llvm/pr-subscribers-llvm-ir

Author: Yingwei Zheng (dtcxzyw)

Changes

Related issues: #68301 #70985 #82381

---

Full diff: https://github.com/llvm/llvm-project/pull/86483.diff

1 Files Affected:

• (added) llvm/include/llvm/IR/ConstantFPRange.h (+139)

diff --git a/llvm/include/llvm/IR/ConstantFPRange.h b/llvm/include/llvm/IR/ConstantFPRange.h
new file mode 100644
index 00000000000000..89b0cd0b7763b5
--- /dev/null
+++ b/llvm/include/llvm/IR/ConstantFPRange.h
@@ -0,0 +1,139 @@
+//===- 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.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_IR_CONSTANTFPRANGE_H
+#define LLVM_IR_CONSTANTFPRANGE_H
+
+#include "llvm/ADT/APFloat.h"
+#include "llvm/IR/InstrTypes.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/Support/Compiler.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;
+  bool SignBitMaybeZero : 1;
+  bool SignBitMaybeOne : 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);
+  }
+
+public:
+  /// Initialize a full or empty set for the specified semantics.
+  explicit ConstantFPRange(const fltSemantics &FloatSema, bool IsFullSet);
+
+  /// Initialize a range to hold the single specified value.
+  ConstantFPRange(const APFloat &Value);
+
+  /// Initialize a range of values explicitly.
+  ConstantFPRange(APFloat Lower, APFloat Upper, bool MaybeQNaN, bool MaybeSNaN,
+                  bool SignBitMaybeZero, bool SignBitMaybeOne);
+
+  /// Create empty constant range with the given semantics.
+  static ConstantFPRange getEmpty(const fltSemantics &FloatSema) {
+    return ConstantFPRange(FloatSema, /*IsFullSet=*/false);
+  }
+
+  /// Create full constant range with the given semantics.
+  static ConstantFPRange getFull(const fltSemantics &FloatSema) {
+    return ConstantFPRange(FloatSema, /*IsFullSet=*/true);
+  }
+
+  /// Initialize a range based on a known floating-point classes constraint.
+  static ConstantFPRange fromKnownFPClass(const KnownFPClass &Known);
+
+  /// 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; }
+
+  /// 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();
+
+  /// Return true if this range is equal to another range.
+  bool operator==(const ConstantFPRange &CR) const;
+  bool operator!=(const ConstantFPRange &CR) const { return !operator==(CR); }
+
+  /// Return known floating-point classes for values in this range.
+  KnownFPClass toKnownFPClass();
+
+  /// Print out the bounds to a stream.
+  void print(raw_ostream &OS) const;
+
+  /// Allow printing from a debugger easily.
+  void dump() const;
+};
+
+inline raw_ostream &operator<<(raw_ostream &OS, const ConstantFPRange &CR) {
+  CR.print(OS);
+  return OS;
+}
+
+} // end namespace llvm
+
+#endif // LLVM_IR_CONSTANTFPRANGE_H

[arsenm]

Don't understand why these would be "MaybeZero" or "MaybeOne". Must be? Maybe would need to default to 1

[arsenm]

Default values for the nan/sign params

[jcranmer-intel]

Not entirely clear to me from the UI whether or not the range is half-open or closed, which tends to matter more for floating-point values than it does for integers.

If it's half-open, then how is one supposed to represent [inf, inf]?

[jcranmer-intel]

Might be worth having different methods for constructing an (x, y) range and a [x, y] range. Or maybe just a helper for (-inf, inf) (aka, all finite values); that seems to be the only common open range.