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

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,86 @@
+//===- 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 are ordered and no 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) {
+      assert(R.getBitWidth() == getBitWidth());
+      Ranges.push_back(R);
+    }
+  }
+  ArrayRef<ConstantRange> rangesRef() const { return Ranges; }
+  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());
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nikic wrote:

`operator[]` already has this assert.

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