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

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,188 @@
+//===- 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;
+
+public:
+  /// Initialize a full or empty set for the specified semantics.
+  explicit ConstantFPRange(const fltSemantics &Sem, bool IsFullSet);
+
+  /// Initialize a range to hold the single specified value.
+  ConstantFPRange(const APFloat &Value);
+
+  /// Initialize a range of values explicitly.
+  ConstantFPRange(APFloat LowerVal, APFloat UpperVal, bool MayBeQNaN = true,
+                  bool MayBeSNaN = true);
+
+  /// 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);
+  }
+
+  /// 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 ConstantRange, the return value will be a
----------------
nikic wrote:

```suggestion
  /// answer is not representable as a ConstantFPRange, the return value will be a
```
etc

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