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 "PassDetail.h"
37 #include "mlir/Dialect/Affine/Analysis/AffineAnalysis.h"
38 #include "mlir/Dialect/Affine/Analysis/LoopAnalysis.h"
39 #include "mlir/Dialect/Affine/IR/AffineOps.h"
40 #include "mlir/Dialect/Affine/LoopUtils.h"
41 #include "mlir/Dialect/Affine/Passes.h"
42 #include "mlir/IR/AffineExpr.h"
43 #include "mlir/IR/AffineMap.h"
44 #include "mlir/IR/BlockAndValueMapping.h"
45 #include "mlir/IR/Builders.h"
46 #include "llvm/ADT/DenseMap.h"
47 #include "llvm/Support/CommandLine.h"
48
49 using namespace mlir;
50
51 #define DEBUG_TYPE "affine-loop-unroll-jam"
52
53 namespace {
54 /// Loop unroll jam pass. Currently, this just unroll jams the first
55 /// outer loop in a Function.
56 struct LoopUnrollAndJam : public AffineLoopUnrollAndJamBase<LoopUnrollAndJam> {
LoopUnrollAndJam__anonc688eb950111::LoopUnrollAndJam57 explicit LoopUnrollAndJam(Optional<unsigned> unrollJamFactor = None) {
58 if (unrollJamFactor)
59 this->unrollJamFactor = *unrollJamFactor;
60 }
61
62 void runOnOperation() override;
63 };
64 } // namespace
65
66 std::unique_ptr<OperationPass<func::FuncOp>>
createLoopUnrollAndJamPass(int unrollJamFactor)67 mlir::createLoopUnrollAndJamPass(int unrollJamFactor) {
68 return std::make_unique<LoopUnrollAndJam>(
69 unrollJamFactor == -1 ? None : Optional<unsigned>(unrollJamFactor));
70 }
71
runOnOperation()72 void LoopUnrollAndJam::runOnOperation() {
73 if (getOperation().isExternal())
74 return;
75
76 // Currently, just the outermost loop from the first loop nest is
77 // unroll-and-jammed by this pass. However, runOnAffineForOp can be called on
78 // any for operation.
79 auto &entryBlock = getOperation().front();
80 if (auto forOp = dyn_cast<AffineForOp>(entryBlock.front()))
81 (void)loopUnrollJamByFactor(forOp, unrollJamFactor);
82 }
83