[llvm] [SandboxVec] Legality boilerplate (PR #108650)

[via llvm-commits]

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+//===- Legality.h -----------------------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Legality checks for the Sandbox Vectorizer.
+//
+
+#ifndef LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_LEGALITY_H
+#define LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_LEGALITY_H
+
+#include "llvm/SandboxIR/SandboxIR.h"
+
+namespace llvm::sandboxir {
+
+class Legality;
+
+enum class LegalityResultID {
+  Widen, ///> Vectorize by combining scalars to a vector.
+};
+
+/// The legality outcome is represented by a class rather than an enum class
+/// because in some cases the legality checks are expensive and look for a
+/// particular instruction that can be passed along to the vectorizer to avoid
+/// repeating the same expensive computation.
+class LegalityResult {
+protected:
+  LegalityResultID ID;
+  /// Only Legality can create LegalityResults.
+  LegalityResult(LegalityResultID ID) : ID(ID) {}
+  friend class Legality;
+
+public:
+  LegalityResultID getSubclassID() const { return ID; }
+};
+
+class Widen final : public LegalityResult {
+  friend class Legality;
+  Widen() : LegalityResult(LegalityResultID::Widen) {}
+
+public:
+  static bool classof(const LegalityResult *From) {
+    return From->getSubclassID() == LegalityResultID::Widen;
+  }
+};
+
+/// Performs the legality analysis and returns a LegalityResult object.
+class Legality {
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vporpo wrote:

LegalityAnalysis is a better name indeed.

https://github.com/llvm/llvm-project/pull/108650