MLIR  16.0.0git
ControlFlowSink.cpp
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1 //===- ControlFlowSink.cpp - Code to perform control-flow sinking ---------===//
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 a basic control-flow sink pass. Control-flow sinking
10 // moves operations whose only uses are in conditionally-executed blocks in to
11 // those blocks so that they aren't executed on paths where their results are
12 // not needed.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "mlir/Transforms/Passes.h"
17 
18 #include "mlir/IR/Dominance.h"
22 
23 namespace mlir {
24 #define GEN_PASS_DEF_CONTROLFLOWSINK
25 #include "mlir/Transforms/Passes.h.inc"
26 } // namespace mlir
27 
28 using namespace mlir;
29 
30 namespace {
31 /// A control-flow sink pass.
32 struct ControlFlowSink : public impl::ControlFlowSinkBase<ControlFlowSink> {
33  void runOnOperation() override;
34 };
35 } // end anonymous namespace
36 
37 void ControlFlowSink::runOnOperation() {
38  auto &domInfo = getAnalysis<DominanceInfo>();
39  getOperation()->walk([&](RegionBranchOpInterface branch) {
40  SmallVector<Region *> regionsToSink;
41  // Get the regions are that known to be executed at most once.
42  getSinglyExecutedRegionsToSink(branch, regionsToSink);
43  // Sink side-effect free operations.
44  numSunk = controlFlowSink(
45  regionsToSink, domInfo,
46  [](Operation *op, Region *) { return isMemoryEffectFree(op); },
47  [](Operation *op, Region *region) {
48  // Move the operation to the beginning of the region's entry block.
49  // This guarantees the preservation of SSA dominance of all of the
50  // operation's uses are in the region.
51  op->moveBefore(&region->front(), region->front().begin());
52  });
53  });
54 }
55 
56 std::unique_ptr<Pass> mlir::createControlFlowSinkPass() {
57  return std::make_unique<ControlFlowSink>();
58 }
Operation is a basic unit of execution within MLIR.
Definition: Operation.h:31
void moveBefore(Operation *existingOp)
Unlink this operation from its current block and insert it right before existingOp which may be in th...
Definition: Operation.cpp:434
This class contains a list of basic blocks and a link to the parent operation it is attached to.
Definition: Region.h:26
Include the generated interface declarations.
void getSinglyExecutedRegionsToSink(RegionBranchOpInterface branch, SmallVectorImpl< Region * > &regions)
Populates regions with regions of the provided region branch op that are executed at most once at tha...
bool isMemoryEffectFree(Operation *op)
Returns true if the given operation is free of memory effects.
std::unique_ptr< Pass > createControlFlowSinkPass()
Creates a pass to perform control-flow sinking.
size_t controlFlowSink(RegionRange regions, DominanceInfo &domInfo, function_ref< bool(Operation *, Region *)> shouldMoveIntoRegion, function_ref< void(Operation *, Region *)> moveIntoRegion)
Given a list of regions, perform control flow sinking on them.