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//===- SCFToEmitC.cpp - SCF to EmitC conversion ---------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements a pass to convert scf.if ops into emitc ops.
//
//===----------------------------------------------------------------------===//
#include "mlir/Conversion/SCFToEmitC/SCFToEmitC.h"
#include "mlir/Dialect/Arith/IR/Arith.h"
#include "mlir/Dialect/EmitC/IR/EmitC.h"
#include "mlir/Dialect/SCF/IR/SCF.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/BuiltinOps.h"
#include "mlir/IR/IRMapping.h"
#include "mlir/IR/MLIRContext.h"
#include "mlir/IR/PatternMatch.h"
#include "mlir/Transforms/DialectConversion.h"
#include "mlir/Transforms/Passes.h"
namespace mlir {
#define GEN_PASS_DEF_SCFTOEMITC
#include "mlir/Conversion/Passes.h.inc"
} // namespace mlir
using namespace mlir;
using namespace mlir::scf;
namespace {
struct SCFToEmitCPass : public impl::SCFToEmitCBase<SCFToEmitCPass> {
void runOnOperation() override;
};
// Lower scf::for to emitc::for, implementing result values using
// emitc::variable's updated within the loop body.
struct ForLowering : public OpRewritePattern<ForOp> {
using OpRewritePattern<ForOp>::OpRewritePattern;
LogicalResult matchAndRewrite(ForOp forOp,
PatternRewriter &rewriter) const override;
};
// Create an uninitialized emitc::variable op for each result of the given op.
template <typename T>
static SmallVector<Value> createVariablesForResults(T op,
PatternRewriter &rewriter) {
SmallVector<Value> resultVariables;
if (!op.getNumResults())
return resultVariables;
Location loc = op->getLoc();
MLIRContext *context = op.getContext();
OpBuilder::InsertionGuard guard(rewriter);
rewriter.setInsertionPoint(op);
for (OpResult result : op.getResults()) {
Type resultType = result.getType();
emitc::OpaqueAttr noInit = emitc::OpaqueAttr::get(context, "");
emitc::VariableOp var =
rewriter.create<emitc::VariableOp>(loc, resultType, noInit);
resultVariables.push_back(var);
}
return resultVariables;
}
// Create a series of assign ops assigning given values to given variables at
// the current insertion point of given rewriter.
static void assignValues(ValueRange values, SmallVector<Value> &variables,
PatternRewriter &rewriter, Location loc) {
for (auto [value, var] : llvm::zip(values, variables))
rewriter.create<emitc::AssignOp>(loc, var, value);
}
static void lowerYield(SmallVector<Value> &resultVariables,
PatternRewriter &rewriter, scf::YieldOp yield) {
Location loc = yield.getLoc();
ValueRange operands = yield.getOperands();
OpBuilder::InsertionGuard guard(rewriter);
rewriter.setInsertionPoint(yield);
assignValues(operands, resultVariables, rewriter, loc);
rewriter.create<emitc::YieldOp>(loc);
rewriter.eraseOp(yield);
}
LogicalResult ForLowering::matchAndRewrite(ForOp forOp,
PatternRewriter &rewriter) const {
Location loc = forOp.getLoc();
// Create an emitc::variable op for each result. These variables will be
// assigned to by emitc::assign ops within the loop body.
SmallVector<Value> resultVariables =
createVariablesForResults(forOp, rewriter);
SmallVector<Value> iterArgsVariables =
createVariablesForResults(forOp, rewriter);
assignValues(forOp.getInits(), iterArgsVariables, rewriter, loc);
emitc::ForOp loweredFor = rewriter.create<emitc::ForOp>(
loc, forOp.getLowerBound(), forOp.getUpperBound(), forOp.getStep());
Block *loweredBody = loweredFor.getBody();
// Erase the auto-generated terminator for the lowered for op.
rewriter.eraseOp(loweredBody->getTerminator());
SmallVector<Value> replacingValues;
replacingValues.push_back(loweredFor.getInductionVar());
replacingValues.append(iterArgsVariables.begin(), iterArgsVariables.end());
rewriter.mergeBlocks(forOp.getBody(), loweredBody, replacingValues);
lowerYield(iterArgsVariables, rewriter,
cast<scf::YieldOp>(loweredBody->getTerminator()));
// Copy iterArgs into results after the for loop.
assignValues(iterArgsVariables, resultVariables, rewriter, loc);
rewriter.replaceOp(forOp, resultVariables);
return success();
}
// Lower scf::if to emitc::if, implementing result values as emitc::variable's
// updated within the then and else regions.
struct IfLowering : public OpRewritePattern<IfOp> {
using OpRewritePattern<IfOp>::OpRewritePattern;
LogicalResult matchAndRewrite(IfOp ifOp,
PatternRewriter &rewriter) const override;
};
} // namespace
LogicalResult IfLowering::matchAndRewrite(IfOp ifOp,
PatternRewriter &rewriter) const {
Location loc = ifOp.getLoc();
// Create an emitc::variable op for each result. These variables will be
// assigned to by emitc::assign ops within the then & else regions.
SmallVector<Value> resultVariables =
createVariablesForResults(ifOp, rewriter);
// Utility function to lower the contents of an scf::if region to an emitc::if
// region. The contents of the scf::if regions is moved into the respective
// emitc::if regions, but the scf::yield is replaced not only with an
// emitc::yield, but also with a sequence of emitc::assign ops that set the
// yielded values into the result variables.
auto lowerRegion = [&resultVariables, &rewriter](Region ®ion,
Region &loweredRegion) {
rewriter.inlineRegionBefore(region, loweredRegion, loweredRegion.end());
Operation *terminator = loweredRegion.back().getTerminator();
lowerYield(resultVariables, rewriter, cast<scf::YieldOp>(terminator));
};
Region &thenRegion = ifOp.getThenRegion();
Region &elseRegion = ifOp.getElseRegion();
bool hasElseBlock = !elseRegion.empty();
auto loweredIf =
rewriter.create<emitc::IfOp>(loc, ifOp.getCondition(), false, false);
Region &loweredThenRegion = loweredIf.getThenRegion();
lowerRegion(thenRegion, loweredThenRegion);
if (hasElseBlock) {
Region &loweredElseRegion = loweredIf.getElseRegion();
lowerRegion(elseRegion, loweredElseRegion);
}
rewriter.replaceOp(ifOp, resultVariables);
return success();
}
void mlir::populateSCFToEmitCConversionPatterns(RewritePatternSet &patterns) {
patterns.add<ForLowering>(patterns.getContext());
patterns.add<IfLowering>(patterns.getContext());
}
void SCFToEmitCPass::runOnOperation() {
RewritePatternSet patterns(&getContext());
populateSCFToEmitCConversionPatterns(patterns);
// Configure conversion to lower out SCF operations.
ConversionTarget target(getContext());
target.addIllegalOp<scf::ForOp, scf::IfOp>();
target.markUnknownOpDynamicallyLegal([](Operation *) { return true; });
if (failed(
applyPartialConversion(getOperation(), target, std::move(patterns))))
signalPassFailure();
}
std::unique_ptr<Pass> mlir::createConvertSCFToEmitCPass() {
return std::make_unique<SCFToEmitCPass>();
}
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