[llvm] [SandboxVec] Add barebones Region class. (PR #108899)
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Mon Sep 16 16:12:40 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Jorge Gorbe Moya (slackito)
<details>
<summary>Changes</summary>
A region identifies a set of vector instructions generated by vectorization passes. The vectorizer can then run a series of RegionPasses on the region, evaluate the cost, and commit/reject the transforms on a region-by-region basis, instead of an entire basic block.
This is heavily based ov @<!-- -->vporpo's prototype. In particular, the doc comment for the Region class is all his. The rest of this commit is mostly boilerplate around a SetVector: getters, iterators, and some debug helpers.
---
Full diff: https://github.com/llvm/llvm-project/pull/108899.diff
3 Files Affected:
- (added) llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/Region.h (+127)
- (modified) llvm/lib/Transforms/Vectorize/CMakeLists.txt (+1)
- (added) llvm/lib/Transforms/Vectorize/SandboxVectorizer/Region.cpp (+52)
``````````diff
diff --git a/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/Region.h b/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/Region.h
new file mode 100644
index 00000000000000..06c432c2c7b839
--- /dev/null
+++ b/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/Region.h
@@ -0,0 +1,127 @@
+//===- 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);
+ /// Removes SBI from the set.
+ void remove(sandboxir::Instruction *SBI);
+ /// Returns true if SBI is in the Region.
+ bool contains(sandboxir::Instruction *SBI) const {
+ return Insts.contains(SBI);
+ }
+ /// Returns true if the Region has no instructions.
+ bool empty() const { return Insts.empty(); }
+
+ using iterator = decltype(Insts.begin());
+ iterator begin() { return Insts.begin(); }
+ iterator end() { return Insts.end(); }
+
+#ifndef NDEBUG
+ /// This is an expensive check, meant for testing.
+ bool operator==(const sandboxir::Region &Other) const;
+ void dump(raw_ostream &OS) const;
+ void dump() const;
+ friend raw_ostream &operator<<(raw_ostream &OS,
+ const sandboxir::Region &Rgn) {
+ Rgn.dump(OS);
+ return OS;
+ }
+#endif
+};
+
+} // namespace sandboxir
+} // namespace llvm
+#endif // LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_REGION_H
diff --git a/llvm/lib/Transforms/Vectorize/CMakeLists.txt b/llvm/lib/Transforms/Vectorize/CMakeLists.txt
index b11631350e8b4e..45b5618305de9f 100644
--- a/llvm/lib/Transforms/Vectorize/CMakeLists.txt
+++ b/llvm/lib/Transforms/Vectorize/CMakeLists.txt
@@ -4,6 +4,7 @@ add_llvm_component_library(LLVMVectorize
LoopVectorizationLegality.cpp
LoopVectorize.cpp
SandboxVectorizer/Passes/BottomUpVec.cpp
+ SandboxVectorizer/Region.cpp
SandboxVectorizer/SandboxVectorizer.cpp
SLPVectorizer.cpp
Vectorize.cpp
diff --git a/llvm/lib/Transforms/Vectorize/SandboxVectorizer/Region.cpp b/llvm/lib/Transforms/Vectorize/SandboxVectorizer/Region.cpp
new file mode 100644
index 00000000000000..91c0d71becd757
--- /dev/null
+++ b/llvm/lib/Transforms/Vectorize/SandboxVectorizer/Region.cpp
@@ -0,0 +1,52 @@
+//===- Region.cpp ---------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Vectorize/SandboxVectorizer/Region.h"
+
+using namespace llvm;
+
+sandboxir::Region::Region(sandboxir::Context &Ctx, sandboxir::BasicBlock &SBBB)
+ : Ctx(Ctx), SBBB(SBBB) {
+ static unsigned StaticRegionID;
+ RegionID = StaticRegionID++;
+}
+
+sandboxir::Region::~Region() {}
+
+void sandboxir::Region::add(sandboxir::Instruction *SBI) {
+ Insts.insert(SBI);
+}
+
+void sandboxir::Region::remove(sandboxir::Instruction *SBI) {
+ Insts.remove(SBI);
+}
+
+#ifndef NDEBUG
+bool sandboxir::Region::operator==(const sandboxir::Region &Other) const {
+ if (Insts.size() != Other.Insts.size())
+ return false;
+ if (!std::is_permutation(Insts.begin(), Insts.end(),
+ Other.Insts.begin()))
+ return false;
+ return true;
+}
+
+void sandboxir::Region::dump(raw_ostream &OS) const {
+ OS << "RegionID: " << getID() << " ScalarCost=" << ScalarCost
+ << " VectorCost=" << VectorCost << "\n";
+ for (auto *I : Insts)
+ OS << *I << "\n";
+}
+
+void sandboxir::Region::dump() const {
+ dump(dbgs());
+ dbgs() << "\n";
+}
+
+#endif // NDEBUG
+
``````````
</details>
https://github.com/llvm/llvm-project/pull/108899
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