mlir/lib/Transforms/ControlFlowSink.cpp

   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"
  19 #include "mlir/Interfaces/ControlFlowInterfaces.h"
  20 #include "mlir/Interfaces/SideEffectInterfaces.h"
  21 #include "mlir/Transforms/ControlFlowSinkUtils.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 }