[llvm] Add the 'initializes' attribute langref and support (PR #84803)

[Arthur Eubanks via llvm-commits]

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@@ -0,0 +1,108 @@
+//===- ConstantRangeList.h - A list of constant range -----------*- 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 list of signed ConstantRange and do NOT support wrap around the
+// end of the numeric range. Ranges in the list should have the same bitwidth.
+// Each range's lower should be less than its upper. Special lists (take 8-bit
+// as an example):
+//
+// {[0, 0)}     = Empty set
+// {[255, 255)} = Full Set
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_IR_CONSTANTRANGELIST_H
+#define LLVM_IR_CONSTANTRANGELIST_H
+
+#include "llvm/ADT/APInt.h"
+#include "llvm/IR/ConstantRange.h"
+#include <cstddef>
+#include <cstdint>
+
+namespace llvm {
+
+class raw_ostream;
+
+/// This class represents a list of constant ranges.
+class [[nodiscard]] ConstantRangeList {
+  SmallVector<ConstantRange, 2> Ranges;
+  // Whether the range list is sorted: [i].lower() < [i+1].lower()
+  bool Sorted = true;
+
+public:
+  /// Initialize a full or empty set for the specified bit width.
+  explicit ConstantRangeList(uint32_t BitWidth, bool isFullSet);
+
+  ConstantRangeList(int64_t Lower, int64_t Upper);
+
+  SmallVectorImpl<ConstantRange>::iterator begin() { return Ranges.begin(); }
+  SmallVectorImpl<ConstantRange>::iterator end() { return Ranges.end(); }
+  SmallVectorImpl<ConstantRange>::const_iterator begin() const {
+    return Ranges.begin();
+  }
+  SmallVectorImpl<ConstantRange>::const_iterator end() const {
+    return Ranges.end();
+  }
+  ConstantRange getRange(unsigned i) const {
+    assert(i < Ranges.size());
+    return Ranges[i];
+  }
+
+  /// Return true if this set contains no members.
+  bool isEmptySet() const {
+    return Ranges.size() == 1 && Ranges[0].isEmptySet();
+  }
+
+  /// Return true if this set contains all of the elements possible
+  /// for this data-type.
+  bool isFullSet() const { return Ranges.size() == 1 && Ranges[0].isFullSet(); }
+
+  /// Get the bit width of this ConstantRangeList.
+  uint32_t getBitWidth() const { return Ranges[0].getBitWidth(); }
+
+  size_t size() const { return Ranges.size(); }
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aeubanks wrote:

the current comment is kinda redundant with the name, I'd be more specific and say "the number of ranges in this ConstantRangeList"

https://github.com/llvm/llvm-project/pull/84803