757 lines
30 KiB
C++
757 lines
30 KiB
C++
//===- LoopPipelining.cpp - Code to perform loop software pipelining-------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements loop software pipelining
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/Dialect/Arith/IR/Arith.h"
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#include "mlir/Dialect/SCF/IR/SCF.h"
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#include "mlir/Dialect/SCF/Transforms/Patterns.h"
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#include "mlir/Dialect/SCF/Transforms/Transforms.h"
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#include "mlir/Dialect/SCF/Utils/Utils.h"
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#include "mlir/IR/IRMapping.h"
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#include "mlir/IR/PatternMatch.h"
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#include "mlir/Support/MathExtras.h"
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#include "mlir/Transforms/RegionUtils.h"
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#include "llvm/ADT/MapVector.h"
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#include "llvm/Support/Debug.h"
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#define DEBUG_TYPE "scf-loop-pipelining"
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#define DBGS() (llvm::dbgs() << "[" DEBUG_TYPE "]: ")
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#define LDBG(X) LLVM_DEBUG(DBGS() << X << "\n")
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using namespace mlir;
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using namespace mlir::scf;
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namespace {
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/// Helper to keep internal information during pipelining transformation.
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struct LoopPipelinerInternal {
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/// Coarse liverange information for ops used across stages.
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struct LiverangeInfo {
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unsigned lastUseStage = 0;
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unsigned defStage = 0;
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};
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protected:
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ForOp forOp;
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unsigned maxStage = 0;
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DenseMap<Operation *, unsigned> stages;
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std::vector<Operation *> opOrder;
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Value ub;
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Value lb;
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Value step;
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bool dynamicLoop;
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PipeliningOption::AnnotationlFnType annotateFn = nullptr;
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bool peelEpilogue;
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PipeliningOption::PredicateOpFn predicateFn = nullptr;
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// When peeling the kernel we generate several version of each value for
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// different stage of the prologue. This map tracks the mapping between
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// original Values in the loop and the different versions
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// peeled from the loop.
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DenseMap<Value, llvm::SmallVector<Value>> valueMapping;
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/// Assign a value to `valueMapping`, this means `val` represents the version
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/// `idx` of `key` in the epilogue.
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void setValueMapping(Value key, Value el, int64_t idx);
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/// Return the defining op of the given value, if the Value is an argument of
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/// the loop return the associated defining op in the loop and its distance to
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/// the Value.
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std::pair<Operation *, int64_t> getDefiningOpAndDistance(Value value);
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/// Return true if the schedule is possible and return false otherwise. A
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/// schedule is correct if all definitions are scheduled before uses.
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bool verifySchedule();
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public:
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/// Initalize the information for the given `op`, return true if it
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/// satisfies the pre-condition to apply pipelining.
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bool initializeLoopInfo(ForOp op, const PipeliningOption &options);
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/// Emits the prologue, this creates `maxStage - 1` part which will contain
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/// operations from stages [0; i], where i is the part index.
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void emitPrologue(RewriterBase &rewriter);
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/// Gather liverange information for Values that are used in a different stage
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/// than its definition.
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llvm::MapVector<Value, LiverangeInfo> analyzeCrossStageValues();
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scf::ForOp createKernelLoop(
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const llvm::MapVector<Value, LiverangeInfo> &crossStageValues,
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RewriterBase &rewriter,
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llvm::DenseMap<std::pair<Value, unsigned>, unsigned> &loopArgMap);
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/// Emits the pipelined kernel. This clones loop operations following user
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/// order and remaps operands defined in a different stage as their use.
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LogicalResult createKernel(
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scf::ForOp newForOp,
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const llvm::MapVector<Value, LiverangeInfo> &crossStageValues,
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const llvm::DenseMap<std::pair<Value, unsigned>, unsigned> &loopArgMap,
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RewriterBase &rewriter);
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/// Emits the epilogue, this creates `maxStage - 1` part which will contain
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/// operations from stages [i; maxStage], where i is the part index.
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void emitEpilogue(RewriterBase &rewriter,
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llvm::SmallVector<Value> &returnValues);
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};
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bool LoopPipelinerInternal::initializeLoopInfo(
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ForOp op, const PipeliningOption &options) {
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LDBG("Start initializeLoopInfo");
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forOp = op;
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ub = forOp.getUpperBound();
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lb = forOp.getLowerBound();
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step = forOp.getStep();
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dynamicLoop = true;
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auto upperBoundCst = getConstantIntValue(ub);
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auto lowerBoundCst = getConstantIntValue(lb);
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auto stepCst = getConstantIntValue(step);
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if (!upperBoundCst || !lowerBoundCst || !stepCst) {
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if (!options.supportDynamicLoops) {
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LDBG("--dynamic loop not supported -> BAIL");
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return false;
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}
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} else {
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int64_t ubImm = upperBoundCst.value();
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int64_t lbImm = lowerBoundCst.value();
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int64_t stepImm = stepCst.value();
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int64_t numIteration = ceilDiv(ubImm - lbImm, stepImm);
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if (numIteration > maxStage) {
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dynamicLoop = false;
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} else if (!options.supportDynamicLoops) {
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LDBG("--fewer loop iterations than pipeline stages -> BAIL");
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return false;
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}
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}
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peelEpilogue = options.peelEpilogue;
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predicateFn = options.predicateFn;
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if ((!peelEpilogue || dynamicLoop) && predicateFn == nullptr) {
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LDBG("--no epilogue or predicate set -> BAIL");
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return false;
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}
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if (dynamicLoop && peelEpilogue) {
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LDBG("--dynamic loop doesn't support epilogue yet -> BAIL");
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return false;
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}
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std::vector<std::pair<Operation *, unsigned>> schedule;
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options.getScheduleFn(forOp, schedule);
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if (schedule.empty()) {
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LDBG("--empty schedule -> BAIL");
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return false;
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}
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opOrder.reserve(schedule.size());
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for (auto &opSchedule : schedule) {
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maxStage = std::max(maxStage, opSchedule.second);
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stages[opSchedule.first] = opSchedule.second;
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opOrder.push_back(opSchedule.first);
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}
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// All operations need to have a stage.
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for (Operation &op : forOp.getBody()->without_terminator()) {
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if (!stages.contains(&op)) {
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op.emitOpError("not assigned a pipeline stage");
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LDBG("--op not assigned a pipeline stage: " << op << " -> BAIL");
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return false;
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}
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}
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if (!verifySchedule()) {
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LDBG("--invalid schedule: " << op << " -> BAIL");
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return false;
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}
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// Currently, we do not support assigning stages to ops in nested regions. The
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// block of all operations assigned a stage should be the single `scf.for`
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// body block.
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for (const auto &[op, stageNum] : stages) {
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(void)stageNum;
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if (op == forOp.getBody()->getTerminator()) {
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op->emitError("terminator should not be assigned a stage");
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LDBG("--terminator should not be assigned stage: " << *op << " -> BAIL");
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return false;
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}
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if (op->getBlock() != forOp.getBody()) {
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op->emitOpError("the owning Block of all operations assigned a stage "
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"should be the loop body block");
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LDBG("--the owning Block of all operations assigned a stage "
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"should be the loop body block: "
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<< *op << " -> BAIL");
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return false;
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}
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}
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// Support only loop-carried dependencies with a distance of one iteration or
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// those defined outside of the loop. This means that any dependency within a
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// loop should either be on the immediately preceding iteration, the current
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// iteration, or on variables whose values are set before entering the loop.
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if (llvm::any_of(forOp.getBody()->getTerminator()->getOperands(),
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[this](Value operand) {
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Operation *def = operand.getDefiningOp();
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return !def ||
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(!stages.contains(def) && forOp->isAncestor(def));
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})) {
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LDBG("--only support loop carried dependency with a distance of 1 or "
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"defined outside of the loop -> BAIL");
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return false;
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}
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annotateFn = options.annotateFn;
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return true;
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}
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/// Compute unrolled cycles of each op (consumer) and verify that each op is
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/// scheduled after its operands (producers) while adjusting for the distance
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/// between producer and consumer.
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bool LoopPipelinerInternal::verifySchedule() {
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int64_t numCylesPerIter = opOrder.size();
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// Pre-compute the unrolled cycle of each op.
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DenseMap<Operation *, int64_t> unrolledCyles;
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for (int64_t cycle = 0; cycle < numCylesPerIter; cycle++) {
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Operation *def = opOrder[cycle];
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auto it = stages.find(def);
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assert(it != stages.end());
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int64_t stage = it->second;
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unrolledCyles[def] = cycle + stage * numCylesPerIter;
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}
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for (Operation *consumer : opOrder) {
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int64_t consumerCycle = unrolledCyles[consumer];
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for (Value operand : consumer->getOperands()) {
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auto [producer, distance] = getDefiningOpAndDistance(operand);
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if (!producer)
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continue;
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auto it = unrolledCyles.find(producer);
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// Skip producer coming from outside the loop.
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if (it == unrolledCyles.end())
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continue;
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int64_t producerCycle = it->second;
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if (consumerCycle < producerCycle - numCylesPerIter * distance) {
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consumer->emitError("operation scheduled before its operands");
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return false;
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}
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}
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}
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return true;
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}
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/// Clone `op` and call `callback` on the cloned op's oeprands as well as any
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/// operands of nested ops that:
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/// 1) aren't defined within the new op or
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/// 2) are block arguments.
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static Operation *
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cloneAndUpdateOperands(RewriterBase &rewriter, Operation *op,
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function_ref<void(OpOperand *newOperand)> callback) {
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Operation *clone = rewriter.clone(*op);
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for (OpOperand &operand : clone->getOpOperands())
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callback(&operand);
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clone->walk([&](Operation *nested) {
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for (OpOperand &operand : nested->getOpOperands()) {
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Operation *def = operand.get().getDefiningOp();
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if ((def && !clone->isAncestor(def)) || isa<BlockArgument>(operand.get()))
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callback(&operand);
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}
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});
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return clone;
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}
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void LoopPipelinerInternal::emitPrologue(RewriterBase &rewriter) {
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// Initialize the iteration argument to the loop initiale values.
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for (auto [arg, operand] :
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llvm::zip(forOp.getRegionIterArgs(), forOp.getInitsMutable())) {
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setValueMapping(arg, operand.get(), 0);
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}
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auto yield = cast<scf::YieldOp>(forOp.getBody()->getTerminator());
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Location loc = forOp.getLoc();
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SmallVector<Value> predicates(maxStage);
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for (int64_t i = 0; i < maxStage; i++) {
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if (dynamicLoop) {
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Type t = ub.getType();
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// pred = ub > lb + (i * step)
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Value iv = rewriter.create<arith::AddIOp>(
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loc, lb,
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rewriter.create<arith::MulIOp>(
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loc, step,
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rewriter.create<arith::ConstantOp>(
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loc, rewriter.getIntegerAttr(t, i))));
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predicates[i] = rewriter.create<arith::CmpIOp>(
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loc, arith::CmpIPredicate::slt, iv, ub);
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}
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// special handling for induction variable as the increment is implicit.
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// iv = lb + i * step
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Type t = lb.getType();
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Value iv = rewriter.create<arith::AddIOp>(
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loc, lb,
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rewriter.create<arith::MulIOp>(
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loc, step,
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rewriter.create<arith::ConstantOp>(loc,
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rewriter.getIntegerAttr(t, i))));
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setValueMapping(forOp.getInductionVar(), iv, i);
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for (Operation *op : opOrder) {
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if (stages[op] > i)
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continue;
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Operation *newOp =
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cloneAndUpdateOperands(rewriter, op, [&](OpOperand *newOperand) {
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auto it = valueMapping.find(newOperand->get());
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if (it != valueMapping.end()) {
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Value replacement = it->second[i - stages[op]];
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newOperand->set(replacement);
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}
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});
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int predicateIdx = i - stages[op];
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if (predicates[predicateIdx]) {
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newOp = predicateFn(rewriter, newOp, predicates[predicateIdx]);
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assert(newOp && "failed to predicate op.");
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}
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rewriter.setInsertionPointAfter(newOp);
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if (annotateFn)
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annotateFn(newOp, PipeliningOption::PipelinerPart::Prologue, i);
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for (unsigned destId : llvm::seq(unsigned(0), op->getNumResults())) {
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setValueMapping(op->getResult(destId), newOp->getResult(destId),
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i - stages[op]);
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// If the value is a loop carried dependency update the loop argument
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// mapping.
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for (OpOperand &operand : yield->getOpOperands()) {
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if (operand.get() != op->getResult(destId))
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continue;
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setValueMapping(forOp.getRegionIterArgs()[operand.getOperandNumber()],
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newOp->getResult(destId), i - stages[op] + 1);
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}
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}
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}
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}
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}
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llvm::MapVector<Value, LoopPipelinerInternal::LiverangeInfo>
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LoopPipelinerInternal::analyzeCrossStageValues() {
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llvm::MapVector<Value, LoopPipelinerInternal::LiverangeInfo> crossStageValues;
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for (Operation *op : opOrder) {
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unsigned stage = stages[op];
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auto analyzeOperand = [&](OpOperand &operand) {
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auto [def, distance] = getDefiningOpAndDistance(operand.get());
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if (!def)
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return;
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auto defStage = stages.find(def);
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if (defStage == stages.end() || defStage->second == stage ||
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defStage->second == stage + distance)
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return;
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assert(stage > defStage->second);
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LiverangeInfo &info = crossStageValues[operand.get()];
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info.defStage = defStage->second;
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info.lastUseStage = std::max(info.lastUseStage, stage);
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};
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for (OpOperand &operand : op->getOpOperands())
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analyzeOperand(operand);
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visitUsedValuesDefinedAbove(op->getRegions(), [&](OpOperand *operand) {
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analyzeOperand(*operand);
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});
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}
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return crossStageValues;
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}
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std::pair<Operation *, int64_t>
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LoopPipelinerInternal::getDefiningOpAndDistance(Value value) {
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int64_t distance = 0;
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if (auto arg = dyn_cast<BlockArgument>(value)) {
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if (arg.getOwner() != forOp.getBody())
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return {nullptr, 0};
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// Ignore induction variable.
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if (arg.getArgNumber() == 0)
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return {nullptr, 0};
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distance++;
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value =
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forOp.getBody()->getTerminator()->getOperand(arg.getArgNumber() - 1);
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}
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Operation *def = value.getDefiningOp();
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if (!def)
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return {nullptr, 0};
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return {def, distance};
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}
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scf::ForOp LoopPipelinerInternal::createKernelLoop(
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const llvm::MapVector<Value, LoopPipelinerInternal::LiverangeInfo>
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&crossStageValues,
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RewriterBase &rewriter,
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llvm::DenseMap<std::pair<Value, unsigned>, unsigned> &loopArgMap) {
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// Creates the list of initial values associated to values used across
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// stages. The initial values come from the prologue created above.
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// Keep track of the kernel argument associated to each version of the
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// values passed to the kernel.
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llvm::SmallVector<Value> newLoopArg;
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// For existing loop argument initialize them with the right version from the
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// prologue.
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for (const auto &retVal :
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llvm::enumerate(forOp.getBody()->getTerminator()->getOperands())) {
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Operation *def = retVal.value().getDefiningOp();
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assert(def && "Only support loop carried dependencies of distance of 1 or "
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"outside the loop");
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auto defStage = stages.find(def);
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if (defStage != stages.end()) {
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Value valueVersion =
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valueMapping[forOp.getRegionIterArgs()[retVal.index()]]
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[maxStage - defStage->second];
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assert(valueVersion);
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newLoopArg.push_back(valueVersion);
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} else
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newLoopArg.push_back(forOp.getInitArgs()[retVal.index()]);
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}
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for (auto escape : crossStageValues) {
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LiverangeInfo &info = escape.second;
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Value value = escape.first;
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for (unsigned stageIdx = 0; stageIdx < info.lastUseStage - info.defStage;
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stageIdx++) {
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Value valueVersion =
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valueMapping[value][maxStage - info.lastUseStage + stageIdx];
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assert(valueVersion);
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newLoopArg.push_back(valueVersion);
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loopArgMap[std::make_pair(value, info.lastUseStage - info.defStage -
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stageIdx)] = newLoopArg.size() - 1;
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}
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}
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// Create the new kernel loop. When we peel the epilgue we need to peel
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// `numStages - 1` iterations. Then we adjust the upper bound to remove those
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// iterations.
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Value newUb = forOp.getUpperBound();
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if (peelEpilogue) {
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Type t = ub.getType();
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Location loc = forOp.getLoc();
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// newUb = ub - maxStage * step
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Value maxStageValue = rewriter.create<arith::ConstantOp>(
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loc, rewriter.getIntegerAttr(t, maxStage));
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Value maxStageByStep =
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rewriter.create<arith::MulIOp>(loc, step, maxStageValue);
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newUb = rewriter.create<arith::SubIOp>(loc, ub, maxStageByStep);
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}
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auto newForOp =
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rewriter.create<scf::ForOp>(forOp.getLoc(), forOp.getLowerBound(), newUb,
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forOp.getStep(), newLoopArg);
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// When there are no iter args, the loop body terminator will be created.
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// Since we always create it below, remove the terminator if it was created.
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if (!newForOp.getBody()->empty())
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rewriter.eraseOp(newForOp.getBody()->getTerminator());
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return newForOp;
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}
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LogicalResult LoopPipelinerInternal::createKernel(
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scf::ForOp newForOp,
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const llvm::MapVector<Value, LoopPipelinerInternal::LiverangeInfo>
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&crossStageValues,
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const llvm::DenseMap<std::pair<Value, unsigned>, unsigned> &loopArgMap,
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RewriterBase &rewriter) {
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valueMapping.clear();
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// Create the kernel, we clone instruction based on the order given by
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// user and remap operands coming from a previous stages.
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rewriter.setInsertionPoint(newForOp.getBody(), newForOp.getBody()->begin());
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IRMapping mapping;
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mapping.map(forOp.getInductionVar(), newForOp.getInductionVar());
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for (const auto &arg : llvm::enumerate(forOp.getRegionIterArgs())) {
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mapping.map(arg.value(), newForOp.getRegionIterArgs()[arg.index()]);
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}
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SmallVector<Value> predicates(maxStage + 1, nullptr);
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if (!peelEpilogue) {
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// Create a predicate for each stage except the last stage.
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Location loc = newForOp.getLoc();
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|
Type t = ub.getType();
|
|
for (unsigned i = 0; i < maxStage; i++) {
|
|
// c = ub - (maxStage - i) * step
|
|
Value c = rewriter.create<arith::SubIOp>(
|
|
loc, ub,
|
|
rewriter.create<arith::MulIOp>(
|
|
loc, step,
|
|
rewriter.create<arith::ConstantOp>(
|
|
loc, rewriter.getIntegerAttr(t, int64_t(maxStage - i)))));
|
|
|
|
Value pred = rewriter.create<arith::CmpIOp>(
|
|
newForOp.getLoc(), arith::CmpIPredicate::slt,
|
|
newForOp.getInductionVar(), c);
|
|
predicates[i] = pred;
|
|
}
|
|
}
|
|
for (Operation *op : opOrder) {
|
|
int64_t useStage = stages[op];
|
|
auto *newOp = rewriter.clone(*op, mapping);
|
|
SmallVector<OpOperand *> operands;
|
|
// Collect all the operands for the cloned op and its nested ops.
|
|
op->walk([&operands](Operation *nestedOp) {
|
|
for (OpOperand &operand : nestedOp->getOpOperands()) {
|
|
operands.push_back(&operand);
|
|
}
|
|
});
|
|
for (OpOperand *operand : operands) {
|
|
Operation *nestedNewOp = mapping.lookup(operand->getOwner());
|
|
// Special case for the induction variable uses. We replace it with a
|
|
// version incremented based on the stage where it is used.
|
|
if (operand->get() == forOp.getInductionVar()) {
|
|
rewriter.setInsertionPoint(newOp);
|
|
|
|
// offset = (maxStage - stages[op]) * step
|
|
Type t = step.getType();
|
|
Value offset = rewriter.create<arith::MulIOp>(
|
|
forOp.getLoc(), step,
|
|
rewriter.create<arith::ConstantOp>(
|
|
forOp.getLoc(),
|
|
rewriter.getIntegerAttr(t, maxStage - stages[op])));
|
|
Value iv = rewriter.create<arith::AddIOp>(
|
|
forOp.getLoc(), newForOp.getInductionVar(), offset);
|
|
nestedNewOp->setOperand(operand->getOperandNumber(), iv);
|
|
rewriter.setInsertionPointAfter(newOp);
|
|
continue;
|
|
}
|
|
Value source = operand->get();
|
|
auto arg = dyn_cast<BlockArgument>(source);
|
|
if (arg && arg.getOwner() == forOp.getBody()) {
|
|
Value ret = forOp.getBody()->getTerminator()->getOperand(
|
|
arg.getArgNumber() - 1);
|
|
Operation *dep = ret.getDefiningOp();
|
|
if (!dep)
|
|
continue;
|
|
auto stageDep = stages.find(dep);
|
|
if (stageDep == stages.end() || stageDep->second == useStage)
|
|
continue;
|
|
// If the value is a loop carried value coming from stage N + 1 remap,
|
|
// it will become a direct use.
|
|
if (stageDep->second == useStage + 1) {
|
|
nestedNewOp->setOperand(operand->getOperandNumber(),
|
|
mapping.lookupOrDefault(ret));
|
|
continue;
|
|
}
|
|
source = ret;
|
|
}
|
|
// For operands defined in a previous stage we need to remap it to use
|
|
// the correct region argument. We look for the right version of the
|
|
// Value based on the stage where it is used.
|
|
Operation *def = source.getDefiningOp();
|
|
if (!def)
|
|
continue;
|
|
auto stageDef = stages.find(def);
|
|
if (stageDef == stages.end() || stageDef->second == useStage)
|
|
continue;
|
|
auto remap = loopArgMap.find(
|
|
std::make_pair(operand->get(), useStage - stageDef->second));
|
|
assert(remap != loopArgMap.end());
|
|
nestedNewOp->setOperand(operand->getOperandNumber(),
|
|
newForOp.getRegionIterArgs()[remap->second]);
|
|
}
|
|
|
|
if (predicates[useStage]) {
|
|
newOp = predicateFn(rewriter, newOp, predicates[useStage]);
|
|
if (!newOp)
|
|
return failure();
|
|
// Remap the results to the new predicated one.
|
|
for (auto values : llvm::zip(op->getResults(), newOp->getResults()))
|
|
mapping.map(std::get<0>(values), std::get<1>(values));
|
|
}
|
|
rewriter.setInsertionPointAfter(newOp);
|
|
if (annotateFn)
|
|
annotateFn(newOp, PipeliningOption::PipelinerPart::Kernel, 0);
|
|
}
|
|
|
|
// Collect the Values that need to be returned by the forOp. For each
|
|
// value we need to have `LastUseStage - DefStage` number of versions
|
|
// returned.
|
|
// We create a mapping between original values and the associated loop
|
|
// returned values that will be needed by the epilogue.
|
|
llvm::SmallVector<Value> yieldOperands;
|
|
for (OpOperand &yieldOperand :
|
|
forOp.getBody()->getTerminator()->getOpOperands()) {
|
|
Value source = mapping.lookupOrDefault(yieldOperand.get());
|
|
// When we don't peel the epilogue and the yield value is used outside the
|
|
// loop we need to make sure we return the version from numStages -
|
|
// defStage.
|
|
if (!peelEpilogue &&
|
|
!forOp.getResult(yieldOperand.getOperandNumber()).use_empty()) {
|
|
Operation *def = getDefiningOpAndDistance(yieldOperand.get()).first;
|
|
if (def) {
|
|
auto defStage = stages.find(def);
|
|
if (defStage != stages.end() && defStage->second < maxStage) {
|
|
Value pred = predicates[defStage->second];
|
|
source = rewriter.create<arith::SelectOp>(
|
|
pred.getLoc(), pred, source,
|
|
newForOp.getBody()
|
|
->getArguments()[yieldOperand.getOperandNumber() + 1]);
|
|
}
|
|
}
|
|
}
|
|
yieldOperands.push_back(source);
|
|
}
|
|
|
|
for (auto &it : crossStageValues) {
|
|
int64_t version = maxStage - it.second.lastUseStage + 1;
|
|
unsigned numVersionReturned = it.second.lastUseStage - it.second.defStage;
|
|
// add the original version to yield ops.
|
|
// If there is a live range spanning across more than 2 stages we need to
|
|
// add extra arg.
|
|
for (unsigned i = 1; i < numVersionReturned; i++) {
|
|
setValueMapping(it.first, newForOp->getResult(yieldOperands.size()),
|
|
version++);
|
|
yieldOperands.push_back(
|
|
newForOp.getBody()->getArguments()[yieldOperands.size() + 1 +
|
|
newForOp.getNumInductionVars()]);
|
|
}
|
|
setValueMapping(it.first, newForOp->getResult(yieldOperands.size()),
|
|
version++);
|
|
yieldOperands.push_back(mapping.lookupOrDefault(it.first));
|
|
}
|
|
// Map the yield operand to the forOp returned value.
|
|
for (const auto &retVal :
|
|
llvm::enumerate(forOp.getBody()->getTerminator()->getOperands())) {
|
|
Operation *def = retVal.value().getDefiningOp();
|
|
assert(def && "Only support loop carried dependencies of distance of 1 or "
|
|
"defined outside the loop");
|
|
auto defStage = stages.find(def);
|
|
if (defStage == stages.end()) {
|
|
for (unsigned int stage = 1; stage <= maxStage; stage++)
|
|
setValueMapping(forOp.getRegionIterArgs()[retVal.index()],
|
|
retVal.value(), stage);
|
|
} else if (defStage->second > 0) {
|
|
setValueMapping(forOp.getRegionIterArgs()[retVal.index()],
|
|
newForOp->getResult(retVal.index()),
|
|
maxStage - defStage->second + 1);
|
|
}
|
|
}
|
|
rewriter.create<scf::YieldOp>(forOp.getLoc(), yieldOperands);
|
|
return success();
|
|
}
|
|
|
|
void LoopPipelinerInternal::emitEpilogue(
|
|
RewriterBase &rewriter, llvm::SmallVector<Value> &returnValues) {
|
|
// Emit different versions of the induction variable. They will be
|
|
// removed by dead code if not used.
|
|
for (int64_t i = 0; i < maxStage; i++) {
|
|
Location loc = forOp.getLoc();
|
|
Type t = lb.getType();
|
|
Value minusOne =
|
|
rewriter.create<arith::ConstantOp>(loc, rewriter.getIntegerAttr(t, -1));
|
|
// number of iterations = ((ub - 1) - lb) / step
|
|
Value totalNumIteration = rewriter.create<arith::DivUIOp>(
|
|
loc,
|
|
rewriter.create<arith::SubIOp>(
|
|
loc, rewriter.create<arith::AddIOp>(loc, ub, minusOne), lb),
|
|
step);
|
|
// newLastIter = lb + step * ((((ub - 1) - lb) / step) - i)
|
|
Value minusI =
|
|
rewriter.create<arith::ConstantOp>(loc, rewriter.getIntegerAttr(t, -i));
|
|
Value newlastIter = rewriter.create<arith::AddIOp>(
|
|
loc, lb,
|
|
rewriter.create<arith::MulIOp>(
|
|
loc, step,
|
|
rewriter.create<arith::AddIOp>(loc, totalNumIteration, minusI)));
|
|
setValueMapping(forOp.getInductionVar(), newlastIter, maxStage - i);
|
|
}
|
|
// Emit `maxStage - 1` epilogue part that includes operations from stages
|
|
// [i; maxStage].
|
|
for (int64_t i = 1; i <= maxStage; i++) {
|
|
for (Operation *op : opOrder) {
|
|
if (stages[op] < i)
|
|
continue;
|
|
Operation *newOp =
|
|
cloneAndUpdateOperands(rewriter, op, [&](OpOperand *newOperand) {
|
|
auto it = valueMapping.find(newOperand->get());
|
|
if (it != valueMapping.end()) {
|
|
Value replacement = it->second[maxStage - stages[op] + i];
|
|
newOperand->set(replacement);
|
|
}
|
|
});
|
|
if (annotateFn)
|
|
annotateFn(newOp, PipeliningOption::PipelinerPart::Epilogue, i - 1);
|
|
for (unsigned destId : llvm::seq(unsigned(0), op->getNumResults())) {
|
|
setValueMapping(op->getResult(destId), newOp->getResult(destId),
|
|
maxStage - stages[op] + i);
|
|
// If the value is a loop carried dependency update the loop argument
|
|
// mapping and keep track of the last version to replace the original
|
|
// forOp uses.
|
|
for (OpOperand &operand :
|
|
forOp.getBody()->getTerminator()->getOpOperands()) {
|
|
if (operand.get() != op->getResult(destId))
|
|
continue;
|
|
unsigned version = maxStage - stages[op] + i + 1;
|
|
// If the version is greater than maxStage it means it maps to the
|
|
// original forOp returned value.
|
|
if (version > maxStage) {
|
|
returnValues[operand.getOperandNumber()] = newOp->getResult(destId);
|
|
continue;
|
|
}
|
|
setValueMapping(forOp.getRegionIterArgs()[operand.getOperandNumber()],
|
|
newOp->getResult(destId), version);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
void LoopPipelinerInternal::setValueMapping(Value key, Value el, int64_t idx) {
|
|
auto it = valueMapping.find(key);
|
|
// If the value is not in the map yet add a vector big enough to store all
|
|
// versions.
|
|
if (it == valueMapping.end())
|
|
it =
|
|
valueMapping
|
|
.insert(std::make_pair(key, llvm::SmallVector<Value>(maxStage + 1)))
|
|
.first;
|
|
it->second[idx] = el;
|
|
}
|
|
|
|
} // namespace
|
|
|
|
FailureOr<ForOp> mlir::scf::pipelineForLoop(RewriterBase &rewriter, ForOp forOp,
|
|
const PipeliningOption &options,
|
|
bool *modifiedIR) {
|
|
if (modifiedIR)
|
|
*modifiedIR = false;
|
|
LoopPipelinerInternal pipeliner;
|
|
if (!pipeliner.initializeLoopInfo(forOp, options))
|
|
return failure();
|
|
|
|
if (modifiedIR)
|
|
*modifiedIR = true;
|
|
|
|
// 1. Emit prologue.
|
|
pipeliner.emitPrologue(rewriter);
|
|
|
|
// 2. Track values used across stages. When a value cross stages it will
|
|
// need to be passed as loop iteration arguments.
|
|
// We first collect the values that are used in a different stage than where
|
|
// they are defined.
|
|
llvm::MapVector<Value, LoopPipelinerInternal::LiverangeInfo>
|
|
crossStageValues = pipeliner.analyzeCrossStageValues();
|
|
|
|
// Mapping between original loop values used cross stage and the block
|
|
// arguments associated after pipelining. A Value may map to several
|
|
// arguments if its liverange spans across more than 2 stages.
|
|
llvm::DenseMap<std::pair<Value, unsigned>, unsigned> loopArgMap;
|
|
// 3. Create the new kernel loop and return the block arguments mapping.
|
|
ForOp newForOp =
|
|
pipeliner.createKernelLoop(crossStageValues, rewriter, loopArgMap);
|
|
// Create the kernel block, order ops based on user choice and remap
|
|
// operands.
|
|
if (failed(pipeliner.createKernel(newForOp, crossStageValues, loopArgMap,
|
|
rewriter)))
|
|
return failure();
|
|
|
|
llvm::SmallVector<Value> returnValues =
|
|
newForOp.getResults().take_front(forOp->getNumResults());
|
|
if (options.peelEpilogue) {
|
|
// 4. Emit the epilogue after the new forOp.
|
|
rewriter.setInsertionPointAfter(newForOp);
|
|
pipeliner.emitEpilogue(rewriter, returnValues);
|
|
}
|
|
// 5. Erase the original loop and replace the uses with the epilogue output.
|
|
if (forOp->getNumResults() > 0)
|
|
rewriter.replaceOp(forOp, returnValues);
|
|
else
|
|
rewriter.eraseOp(forOp);
|
|
|
|
return newForOp;
|
|
}
|
|
|
|
void mlir::scf::populateSCFLoopPipeliningPatterns(
|
|
RewritePatternSet &patterns, const PipeliningOption &options) {
|
|
patterns.add<ForLoopPipeliningPattern>(options, patterns.getContext());
|
|
}
|