[llvm] [SandboxVec] Add barebones Region class. (PR #108899)

[via llvm-commits]

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+//===- Region.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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_REGION_H
+#define LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_REGION_H
+
+#include "llvm/ADT/SetVector.h"
+#include "llvm/SandboxIR/SandboxIR.h"
+#include "llvm/Support/InstructionCost.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace llvm {
+namespace sandboxir {
+
+/// The main job of the Region is to point to new instructions generated by
+/// vectorization passes. It is the unit that RegionPasses operate on with their
+/// runOnRegion() function.
+///
+/// The region allows us to stack transformations horizontally, meaning that
+/// each transformation operates on a single region and the resulting region is
+/// the input to the next transformation, as opposed to vertically, which is the
+/// common way of applying a transformation across the whole BB. This enables us
+/// to check for profitability and decide whether we accept or rollback at a
+/// region granularity, which is much better than doing this at the BB level.
+///
+/// The region keeps track of the costs that correspond to that region. That is
+/// the original "scalar" cost and the new "vector" cost. The cost is updated
+/// automatically via SandboxIR callbacks:
+/// (i) Upon deletion: If the deleted instruction is not in the region, it is an
+/// original scalar, so its cost is added to the "scalar cost", otherwise it is
+/// a "vector" instruction created by the vectorizer so we subtract its cost
+/// from the "vector cost".
+/// (ii) Upon creation: New instructions are always considered "vector" so its
+/// cost is added to the "vector cost".
+/// This cost tracking allows us to start with transformations that may not be
+/// profitable if applied by themselves, but may end up being profitable after a
+/// series of transformations.
+///
+//  Traditional approach: transformations applied vertically for the whole BB
+//    BB
+//  +----+
+//  |    |
+//  |    |
+//  |    | -> Transform1 ->  ... -> TransformN -> Check Cost
+//  |    |
+//  |    |
+//  +----+
+//
+//  Region-based approach: transformations applied horizontally, for each Region
+//    BB
+//  +----+
+//  |Rgn1| -> Transform1 ->  ... -> TransformN -> Check Cost
+//  |    |
+//  |Rgn2| -> Transform1 ->  ... -> TransformN -> Check Cost
+//  |    |
+//  |Rgn3| -> Transform1 ->  ... -> TransformN -> Check Cost
+//  +----+
+
+class Region {
+  /// All the instructions in the Region. Only new instructions generated during
+  /// vectorization are part of the Region.
+  SetVector<sandboxir::Instruction *> Insts;
+
+  /// A unique ID, used for debugging.
+  unsigned RegionID = 0;
+
+  sandboxir::Context &Ctx;
+
+  /// The basic block containing this region.
+  sandboxir::BasicBlock &SBBB;
+
+  // TODO: Add cost modeling.
+
+  /// The cost of the original scalar instructions replaced by vector
+  /// instructions in this region.
+  InstructionCost ScalarCost;
+
+  /// The cost of the vector instructions in the region.
+  InstructionCost VectorCost;
+
+  // TODO: Add a way to encode/decode region info to/from metadata.
+
+public:
+  Region(sandboxir::Context &Ctx, sandboxir::BasicBlock &SBBB);
+  ~Region();
+
+  sandboxir::BasicBlock *getParent() const { return &SBBB; }
+  sandboxir::Context &getContext() const { return Ctx; }
+  /// Returns the region's unique ID.
+  unsigned getID() const { return RegionID; }
+
+  /// Adds SBI to the set.
+  void add(sandboxir::Instruction *SBI);
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vporpo wrote:

Same here, rename `SBI` to `I`.

https://github.com/llvm/llvm-project/pull/108899