1 //===- LoopUnrollAndJam.cpp - Code to perform loop unroll and jam ---------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements loop unroll and jam. Unroll and jam is a transformation
10 // that improves locality, in particular, register reuse, while also improving
11 // operation level parallelism. The example below shows what it does in nearly
12 // the general case. Loop unroll and jam currently works if the bounds of the
13 // loops inner to the loop being unroll-jammed do not depend on the latter.
14 //
15 // Before After unroll and jam of i by factor 2:
16 //
17 // for i, step = 2
18 // for i S1(i);
19 // S1; S2(i);
20 // S2; S1(i+1);
21 // for j S2(i+1);
22 // S3; for j
23 // S4; S3(i, j);
24 // S5; S4(i, j);
25 // S6; S3(i+1, j)
26 // S4(i+1, j)
27 // S5(i);
28 // S6(i);
29 // S5(i+1);
30 // S6(i+1);
31 //
32 // Note: 'if/else' blocks are not jammed. So, if there are loops inside if
33 // op's, bodies of those loops will not be jammed.
34 //===----------------------------------------------------------------------===//
35
36 #include "mlir/Dialect/Affine/Passes.h"
37
38 #include "mlir/Dialect/Affine/Analysis/AffineAnalysis.h"
39 #include "mlir/Dialect/Affine/Analysis/LoopAnalysis.h"
40 #include "mlir/Dialect/Affine/IR/AffineOps.h"
41 #include "mlir/Dialect/Affine/LoopUtils.h"
42 #include "mlir/Dialect/Func/IR/FuncOps.h"
43 #include "mlir/IR/AffineExpr.h"
44 #include "mlir/IR/AffineMap.h"
45 #include "mlir/IR/Builders.h"
46 #include "mlir/IR/IRMapping.h"
47 #include "llvm/ADT/DenseMap.h"
48 #include "llvm/Support/CommandLine.h"
49 #include <optional>
50
51 namespace mlir {
52 namespace affine {
53 #define GEN_PASS_DEF_AFFINELOOPUNROLLANDJAM
54 #include "mlir/Dialect/Affine/Passes.h.inc"
55 } // namespace affine
56 } // namespace mlir
57
58 #define DEBUG_TYPE "affine-loop-unroll-jam"
59
60 using namespace mlir;
61 using namespace mlir::affine;
62
63 namespace {
64 /// Loop unroll jam pass. Currently, this just unroll jams the first
65 /// outer loop in a Function.
66 struct LoopUnrollAndJam
67 : public affine::impl::AffineLoopUnrollAndJamBase<LoopUnrollAndJam> {
LoopUnrollAndJam__anonddc5f8580111::LoopUnrollAndJam68 explicit LoopUnrollAndJam(
69 std::optional<unsigned> unrollJamFactor = std::nullopt) {
70 if (unrollJamFactor)
71 this->unrollJamFactor = *unrollJamFactor;
72 }
73
74 void runOnOperation() override;
75 };
76 } // namespace
77
78 std::unique_ptr<OperationPass<func::FuncOp>>
createLoopUnrollAndJamPass(int unrollJamFactor)79 mlir::affine::createLoopUnrollAndJamPass(int unrollJamFactor) {
80 return std::make_unique<LoopUnrollAndJam>(
81 unrollJamFactor == -1 ? std::nullopt
82 : std::optional<unsigned>(unrollJamFactor));
83 }
84
runOnOperation()85 void LoopUnrollAndJam::runOnOperation() {
86 if (getOperation().isExternal())
87 return;
88
89 // Currently, just the outermost loop from the first loop nest is
90 // unroll-and-jammed by this pass. However, runOnAffineForOp can be called on
91 // any for operation.
92 auto &entryBlock = getOperation().front();
93 if (auto forOp = dyn_cast<AffineForOp>(entryBlock.front()))
94 (void)loopUnrollJamByFactor(forOp, unrollJamFactor);
95 }
96