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

[Arthur Eubanks via llvm-commits]

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@@ -0,0 +1,87 @@
+//===- ConstantRangeList.h - A list of constant ranges ----------*- 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 are ordered and not overlapping.
+// Ranges should have the same bitwidth. Each range's lower should be less than
+// its upper.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_IR_CONSTANTRANGELIST_H
+#define LLVM_IR_CONSTANTRANGELIST_H
+
+#include "llvm/ADT/APInt.h"
+#include "llvm/IR/ConstantRange.h"
+#include "llvm/Support/Debug.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;
+
+public:
+  ConstantRangeList() = default;
+  ConstantRangeList(ArrayRef<ConstantRange> RangesRef) {
+    for (const ConstantRange &R : RangesRef) {
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aeubanks wrote:

add asserts that these are non-overlapping and increasing

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