SquashSimTriggered.cpp

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//===- SquashSimTriggered.cpp - Merge sim.triggered ops by clock ---------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Merge multiple sim.triggered ops in the same block that share a clock into a
// single sim.triggered. Conditions that cannot be represented on the merged op
// directly are materialized as scf.if operations inside the merged body.
//
//===----------------------------------------------------------------------===//
 
#include "circt/Dialect/HW/HWOps.h"
#include "circt/Dialect/Seq/SeqOps.h"
#include "circt/Dialect/Sim/SimOps.h"
#include "circt/Dialect/Sim/SimPasses.h"
#include "mlir/Dialect/SCF/IR/SCF.h"
#include "mlir/Pass/Pass.h"
#include "mlir/Transforms/RegionUtils.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SetVector.h"
 
namespace circt {
namespace sim {
#define GEN_PASS_DEF_SQUASHSIMTRIGGERED
#include "circt/Dialect/Sim/SimPasses.h.inc"
} // namespace sim
} // namespace circt
 
using namespace circt;
using namespace sim;
 
namespace {
 
static Block *getOrCreateConditionBlock(OpBuilder &builder, Location loc,
                                        Value condition,
                                        Value &prevConditionValue,
                                        Block *&prevConditionBlock) {
  if (condition != prevConditionValue)
    prevConditionBlock = nullptr;
 
  if (prevConditionBlock)
    return prevConditionBlock;
 
  auto ifOp = mlir::scf::IfOp::create(builder, loc, TypeRange{}, condition,
                                      true, false);
  builder.setInsertionPointToStart(&ifOp.getThenRegion().front());
  mlir::scf::YieldOp::create(builder, loc);
  prevConditionValue = condition;
  prevConditionBlock = builder.getBlock();
  return prevConditionBlock;
}
 
static void moveBodyOperations(Block *source, Block *dest,
                               Block::iterator insertPt) {
  dest->getOperations().splice(insertPt, source->getOperations(),
                               source->begin(), source->end());
}
 
static void finalizeHWTriggered(hw::TriggeredOp op) {
  mlir::IRRewriter builder(op->getContext());
  auto captures = mlir::makeRegionIsolatedFromAbove(builder, op.getBody());
  op.getInputsMutable().append(captures);
}
 
struct SquashSimTriggeredPass
    : impl::SquashSimTriggeredBase<SquashSimTriggeredPass> {
public:
  using SquashSimTriggeredBase::SquashSimTriggeredBase;
  void runOnOperation() override;
 
private:
  bool squashTriggeredOpsInBlock(Block &block);
};
 
} // namespace
 
bool SquashSimTriggeredPass::squashTriggeredOpsInBlock(Block &block) {
  // Group all top-level sim.triggered ops in this block by their clock.
  SmallMapVector<Value, SmallVector<TriggeredOp>, 2> triggerMap;
  for (Operation &op : block)
    if (auto triggered = dyn_cast<TriggeredOp>(op))
      triggerMap[triggered.getClock()].push_back(triggered);
 
  bool changed = false;
  for (auto &[clock, triggers] : triggerMap) {
    if (triggers.size() < 2 && !convertToHW)
      continue;
 
    SmallVector<Location> locs;
    locs.reserve(triggers.size());
 
    bool hasUnconditionalTrigger = false;
    Value commonCondition;
    bool allConditionsIdentical = true;
    for (auto triggered : triggers) {
      locs.push_back(triggered.getLoc());
      if (auto condition = triggered.getCondition()) {
        if (!commonCondition)
          commonCondition = condition;
        else if (condition != commonCondition)
          allConditionsIdentical = false;
      } else {
        hasUnconditionalTrigger = true;
      }
    }
 
    // Hoist a shared condition to the merged sim.triggered when possible. When
    // converting to hw.triggered, keep all conditions inside the body instead.
    Value outerCondition;
    if (!convertToHW && !hasUnconditionalTrigger && allConditionsIdentical)
      outerCondition = commonCondition;
 
    OpBuilder builder(triggers.back());
    auto fusedLoc = builder.getFusedLoc(locs);
 
    Block *mergedBlock = nullptr;
    hw::TriggeredOp hwTriggered;
    TriggeredOp mergedTriggered;
    if (convertToHW) {
      auto event = hw::EventControlAttr::get(builder.getContext(),
                                             hw::EventControl::AtPosEdge);
      auto trigger = builder.createOrFold<seq::FromClockOp>(fusedLoc, clock);
      hwTriggered = hw::TriggeredOp::create(builder, fusedLoc, event, trigger,
                                            ValueRange{});
      mergedBlock = hwTriggered.getBodyBlock();
    } else {
      mergedTriggered =
          TriggeredOp::create(builder, fusedLoc, clock, outerCondition);
      mergedBlock = mergedTriggered.getBodyBlock();
    }
 
    Value prevConditionValue;
    Block *prevConditionBlock = nullptr;
    for (auto triggered : triggers) {
      auto condition = triggered.getCondition();
      auto *sourceBlock = triggered.getBodyBlock();
 
      // Conditions not represented on the outer op become inner scf.if guards.
      if (!sourceBlock->empty() && condition && condition != outerCondition) {
        builder.setInsertionPointToEnd(mergedBlock);
        auto *condBlock =
            getOrCreateConditionBlock(builder, triggered.getLoc(), condition,
                                      prevConditionValue, prevConditionBlock);
        moveBodyOperations(sourceBlock, condBlock,
                           Block::iterator(condBlock->getTerminator()));
      } else {
        prevConditionValue = Value();
        prevConditionBlock = nullptr;
        moveBodyOperations(sourceBlock, mergedBlock, mergedBlock->end());
      }
 
      triggered.erase();
    }
    if (convertToHW)
      finalizeHWTriggered(hwTriggered);
    changed = true;
  }
 
  return changed;
}
 
void SquashSimTriggeredPass::runOnOperation() {
  hw::HWModuleOp module = getOperation();
  bool changed = squashTriggeredOpsInBlock(*module.getBodyBlock());
  if (!changed)
    markAllAnalysesPreserved();
}