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|
//===- SCFToControlFlow.cpp - SCF to CF 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.for, scf.if and loop.terminator
// ops into standard CFG ops.
//
//===----------------------------------------------------------------------===//
#include "mlir/Conversion/SCFToControlFlow/SCFToControlFlow.h"
#include "mlir/Dialect/Arith/IR/Arith.h"
#include "mlir/Dialect/ControlFlow/IR/ControlFlowOps.h"
#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
#include "mlir/Dialect/SCF/IR/SCF.h"
#include "mlir/Dialect/SCF/Transforms/Transforms.h"
#include "mlir/IR/Builders.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_SCFTOCONTROLFLOWPASS
#include "mlir/Conversion/Passes.h.inc"
} // namespace mlir
using namespace mlir;
using namespace mlir::scf;
namespace {
struct SCFToControlFlowPass
: public impl::SCFToControlFlowPassBase<SCFToControlFlowPass> {
void runOnOperation() override;
};
// Create a CFG subgraph for the loop around its body blocks (if the body
// contained other loops, they have been already lowered to a flow of blocks).
// Maintain the invariants that a CFG subgraph created for any loop has a single
// entry and a single exit, and that the entry/exit blocks are respectively
// first/last blocks in the parent region. The original loop operation is
// replaced by the initialization operations that set up the initial value of
// the loop induction variable (%iv) and computes the loop bounds that are loop-
// invariant for affine loops. The operations following the original scf.for
// are split out into a separate continuation (exit) block. A condition block is
// created before the continuation block. It checks the exit condition of the
// loop and branches either to the continuation block, or to the first block of
// the body. The condition block takes as arguments the values of the induction
// variable followed by loop-carried values. Since it dominates both the body
// blocks and the continuation block, loop-carried values are visible in all of
// those blocks. Induction variable modification is appended to the last block
// of the body (which is the exit block from the body subgraph thanks to the
// invariant we maintain) along with a branch that loops back to the condition
// block. Loop-carried values are the loop terminator operands, which are
// forwarded to the branch.
//
// +---------------------------------+
// | <code before the ForOp> |
// | <definitions of %init...> |
// | <compute initial %iv value> |
// | cf.br cond(%iv, %init...) |
// +---------------------------------+
// |
// -------| |
// | v v
// | +--------------------------------+
// | | cond(%iv, %init...): |
// | | <compare %iv to upper bound> |
// | | cf.cond_br %r, body, end |
// | +--------------------------------+
// | | |
// | | -------------|
// | v |
// | +--------------------------------+ |
// | | body-first: | |
// | | <%init visible by dominance> | |
// | | <body contents> | |
// | +--------------------------------+ |
// | | |
// | ... |
// | | |
// | +--------------------------------+ |
// | | body-last: | |
// | | <body contents> | |
// | | <operands of yield = %yields>| |
// | | %new_iv =<add step to %iv> | |
// | | cf.br cond(%new_iv, %yields) | |
// | +--------------------------------+ |
// | | |
// |----------- |--------------------
// v
// +--------------------------------+
// | end: |
// | <code after the ForOp> |
// | <%init visible by dominance> |
// +--------------------------------+
//
struct ForLowering : public OpRewritePattern<ForOp> {
using OpRewritePattern<ForOp>::OpRewritePattern;
LogicalResult matchAndRewrite(ForOp forOp,
PatternRewriter &rewriter) const override;
};
// Create a CFG subgraph for the scf.if operation (including its "then" and
// optional "else" operation blocks). We maintain the invariants that the
// subgraph has a single entry and a single exit point, and that the entry/exit
// blocks are respectively the first/last block of the enclosing region. The
// operations following the scf.if are split into a continuation (subgraph
// exit) block. The condition is lowered to a chain of blocks that implement the
// short-circuit scheme. The "scf.if" operation is replaced with a conditional
// branch to either the first block of the "then" region, or to the first block
// of the "else" region. In these blocks, "scf.yield" is unconditional branches
// to the post-dominating block. When the "scf.if" does not return values, the
// post-dominating block is the same as the continuation block. When it returns
// values, the post-dominating block is a new block with arguments that
// correspond to the values returned by the "scf.if" that unconditionally
// branches to the continuation block. This allows block arguments to dominate
// any uses of the hitherto "scf.if" results that they replaced. (Inserting a
// new block allows us to avoid modifying the argument list of an existing
// block, which is illegal in a conversion pattern). When the "else" region is
// empty, which is only allowed for "scf.if"s that don't return values, the
// condition branches directly to the continuation block.
//
// CFG for a scf.if with else and without results.
//
// +--------------------------------+
// | <code before the IfOp> |
// | cf.cond_br %cond, %then, %else |
// +--------------------------------+
// | |
// | --------------|
// v |
// +--------------------------------+ |
// | then: | |
// | <then contents> | |
// | cf.br continue | |
// +--------------------------------+ |
// | |
// |---------- |-------------
// | V
// | +--------------------------------+
// | | else: |
// | | <else contents> |
// | | cf.br continue |
// | +--------------------------------+
// | |
// ------| |
// v v
// +--------------------------------+
// | continue: |
// | <code after the IfOp> |
// +--------------------------------+
//
// CFG for a scf.if with results.
//
// +--------------------------------+
// | <code before the IfOp> |
// | cf.cond_br %cond, %then, %else |
// +--------------------------------+
// | |
// | --------------|
// v |
// +--------------------------------+ |
// | then: | |
// | <then contents> | |
// | cf.br dom(%args...) | |
// +--------------------------------+ |
// | |
// |---------- |-------------
// | V
// | +--------------------------------+
// | | else: |
// | | <else contents> |
// | | cf.br dom(%args...) |
// | +--------------------------------+
// | |
// ------| |
// v v
// +--------------------------------+
// | dom(%args...): |
// | cf.br continue |
// +--------------------------------+
// |
// v
// +--------------------------------+
// | continue: |
// | <code after the IfOp> |
// +--------------------------------+
//
struct IfLowering : public OpRewritePattern<IfOp> {
using OpRewritePattern<IfOp>::OpRewritePattern;
LogicalResult matchAndRewrite(IfOp ifOp,
PatternRewriter &rewriter) const override;
};
struct ExecuteRegionLowering : public OpRewritePattern<ExecuteRegionOp> {
using OpRewritePattern<ExecuteRegionOp>::OpRewritePattern;
LogicalResult matchAndRewrite(ExecuteRegionOp op,
PatternRewriter &rewriter) const override;
};
struct ParallelLowering : public OpRewritePattern<mlir::scf::ParallelOp> {
using OpRewritePattern<mlir::scf::ParallelOp>::OpRewritePattern;
LogicalResult matchAndRewrite(mlir::scf::ParallelOp parallelOp,
PatternRewriter &rewriter) const override;
};
/// Create a CFG subgraph for this loop construct. The regions of the loop need
/// not be a single block anymore (for example, if other SCF constructs that
/// they contain have been already converted to CFG), but need to be single-exit
/// from the last block of each region. The operations following the original
/// WhileOp are split into a new continuation block. Both regions of the WhileOp
/// are inlined, and their terminators are rewritten to organize the control
/// flow implementing the loop as follows.
///
/// +---------------------------------+
/// | <code before the WhileOp> |
/// | cf.br ^before(%operands...) |
/// +---------------------------------+
/// |
/// -------| |
/// | v v
/// | +--------------------------------+
/// | | ^before(%bargs...): |
/// | | %vals... = <some payload> |
/// | +--------------------------------+
/// | |
/// | ...
/// | |
/// | +--------------------------------+
/// | | ^before-last:
/// | | %cond = <compute condition> |
/// | | cf.cond_br %cond, |
/// | | ^after(%vals...), ^cont |
/// | +--------------------------------+
/// | | |
/// | | -------------|
/// | v |
/// | +--------------------------------+ |
/// | | ^after(%aargs...): | |
/// | | <body contents> | |
/// | +--------------------------------+ |
/// | | |
/// | ... |
/// | | |
/// | +--------------------------------+ |
/// | | ^after-last: | |
/// | | %yields... = <some payload> | |
/// | | cf.br ^before(%yields...) | |
/// | +--------------------------------+ |
/// | | |
/// |----------- |--------------------
/// v
/// +--------------------------------+
/// | ^cont: |
/// | <code after the WhileOp> |
/// | <%vals from 'before' region |
/// | visible by dominance> |
/// +--------------------------------+
///
/// Values are communicated between ex-regions (the groups of blocks that used
/// to form a region before inlining) through block arguments of their
/// entry blocks, which are visible in all other dominated blocks. Similarly,
/// the results of the WhileOp are defined in the 'before' region, which is
/// required to have a single existing block, and are therefore accessible in
/// the continuation block due to dominance.
struct WhileLowering : public OpRewritePattern<WhileOp> {
using OpRewritePattern<WhileOp>::OpRewritePattern;
LogicalResult matchAndRewrite(WhileOp whileOp,
PatternRewriter &rewriter) const override;
};
/// Optimized version of the above for the case of the "after" region merely
/// forwarding its arguments back to the "before" region (i.e., a "do-while"
/// loop). This avoid inlining the "after" region completely and branches back
/// to the "before" entry instead.
struct DoWhileLowering : public OpRewritePattern<WhileOp> {
using OpRewritePattern<WhileOp>::OpRewritePattern;
LogicalResult matchAndRewrite(WhileOp whileOp,
PatternRewriter &rewriter) const override;
};
/// Lower an `scf.index_switch` operation to a `cf.switch` operation.
struct IndexSwitchLowering : public OpRewritePattern<IndexSwitchOp> {
using OpRewritePattern::OpRewritePattern;
LogicalResult matchAndRewrite(IndexSwitchOp op,
PatternRewriter &rewriter) const override;
};
/// Lower an `scf.forall` operation to an `scf.parallel` op, assuming that it
/// has no shared outputs. Ops with shared outputs should be bufferized first.
/// Specialized lowerings for `scf.forall` (e.g., for GPUs) exist in other
/// dialects/passes.
struct ForallLowering : public OpRewritePattern<mlir::scf::ForallOp> {
using OpRewritePattern<mlir::scf::ForallOp>::OpRewritePattern;
LogicalResult matchAndRewrite(mlir::scf::ForallOp forallOp,
PatternRewriter &rewriter) const override;
};
} // namespace
LogicalResult ForLowering::matchAndRewrite(ForOp forOp,
PatternRewriter &rewriter) const {
Location loc = forOp.getLoc();
// Start by splitting the block containing the 'scf.for' into two parts.
// The part before will get the init code, the part after will be the end
// point.
auto *initBlock = rewriter.getInsertionBlock();
auto initPosition = rewriter.getInsertionPoint();
auto *endBlock = rewriter.splitBlock(initBlock, initPosition);
// Use the first block of the loop body as the condition block since it is the
// block that has the induction variable and loop-carried values as arguments.
// Split out all operations from the first block into a new block. Move all
// body blocks from the loop body region to the region containing the loop.
auto *conditionBlock = &forOp.getRegion().front();
auto *firstBodyBlock =
rewriter.splitBlock(conditionBlock, conditionBlock->begin());
auto *lastBodyBlock = &forOp.getRegion().back();
rewriter.inlineRegionBefore(forOp.getRegion(), endBlock);
auto iv = conditionBlock->getArgument(0);
// Append the induction variable stepping logic to the last body block and
// branch back to the condition block. Loop-carried values are taken from
// operands of the loop terminator.
Operation *terminator = lastBodyBlock->getTerminator();
rewriter.setInsertionPointToEnd(lastBodyBlock);
auto step = forOp.getStep();
auto stepped = arith::AddIOp::create(rewriter, loc, iv, step).getResult();
if (!stepped)
return failure();
SmallVector<Value, 8> loopCarried;
loopCarried.push_back(stepped);
loopCarried.append(terminator->operand_begin(), terminator->operand_end());
auto branchOp =
cf::BranchOp::create(rewriter, loc, conditionBlock, loopCarried);
// Let the CondBranchOp carry the LLVM attributes from the ForOp, such as the
// llvm.loop_annotation attribute.
// LLVM requires the loop metadata to be attached on the "latch" block. Which
// is the back-edge to the header block (conditionBlock)
SmallVector<NamedAttribute> llvmAttrs;
llvm::copy_if(forOp->getAttrs(), std::back_inserter(llvmAttrs),
[](auto attr) {
return isa<LLVM::LLVMDialect>(attr.getValue().getDialect());
});
branchOp->setDiscardableAttrs(llvmAttrs);
rewriter.eraseOp(terminator);
// Compute loop bounds before branching to the condition.
rewriter.setInsertionPointToEnd(initBlock);
Value lowerBound = forOp.getLowerBound();
Value upperBound = forOp.getUpperBound();
if (!lowerBound || !upperBound)
return failure();
// The initial values of loop-carried values is obtained from the operands
// of the loop operation.
SmallVector<Value, 8> destOperands;
destOperands.push_back(lowerBound);
llvm::append_range(destOperands, forOp.getInitArgs());
cf::BranchOp::create(rewriter, loc, conditionBlock, destOperands);
// With the body block done, we can fill in the condition block.
rewriter.setInsertionPointToEnd(conditionBlock);
auto comparison = arith::CmpIOp::create(
rewriter, loc, arith::CmpIPredicate::slt, iv, upperBound);
cf::CondBranchOp::create(rewriter, loc, comparison, firstBodyBlock,
ArrayRef<Value>(), endBlock, ArrayRef<Value>());
// The result of the loop operation is the values of the condition block
// arguments except the induction variable on the last iteration.
rewriter.replaceOp(forOp, conditionBlock->getArguments().drop_front());
return success();
}
LogicalResult IfLowering::matchAndRewrite(IfOp ifOp,
PatternRewriter &rewriter) const {
auto loc = ifOp.getLoc();
// Start by splitting the block containing the 'scf.if' into two parts.
// The part before will contain the condition, the part after will be the
// continuation point.
auto *condBlock = rewriter.getInsertionBlock();
auto opPosition = rewriter.getInsertionPoint();
auto *remainingOpsBlock = rewriter.splitBlock(condBlock, opPosition);
Block *continueBlock;
if (ifOp.getNumResults() == 0) {
continueBlock = remainingOpsBlock;
} else {
continueBlock =
rewriter.createBlock(remainingOpsBlock, ifOp.getResultTypes(),
SmallVector<Location>(ifOp.getNumResults(), loc));
cf::BranchOp::create(rewriter, loc, remainingOpsBlock);
}
// Move blocks from the "then" region to the region containing 'scf.if',
// place it before the continuation block, and branch to it.
auto &thenRegion = ifOp.getThenRegion();
auto *thenBlock = &thenRegion.front();
Operation *thenTerminator = thenRegion.back().getTerminator();
ValueRange thenTerminatorOperands = thenTerminator->getOperands();
rewriter.setInsertionPointToEnd(&thenRegion.back());
cf::BranchOp::create(rewriter, loc, continueBlock, thenTerminatorOperands);
rewriter.eraseOp(thenTerminator);
rewriter.inlineRegionBefore(thenRegion, continueBlock);
// Move blocks from the "else" region (if present) to the region containing
// 'scf.if', place it before the continuation block and branch to it. It
// will be placed after the "then" regions.
auto *elseBlock = continueBlock;
auto &elseRegion = ifOp.getElseRegion();
if (!elseRegion.empty()) {
elseBlock = &elseRegion.front();
Operation *elseTerminator = elseRegion.back().getTerminator();
ValueRange elseTerminatorOperands = elseTerminator->getOperands();
rewriter.setInsertionPointToEnd(&elseRegion.back());
cf::BranchOp::create(rewriter, loc, continueBlock, elseTerminatorOperands);
rewriter.eraseOp(elseTerminator);
rewriter.inlineRegionBefore(elseRegion, continueBlock);
}
rewriter.setInsertionPointToEnd(condBlock);
cf::CondBranchOp::create(rewriter, loc, ifOp.getCondition(), thenBlock,
/*trueArgs=*/ArrayRef<Value>(), elseBlock,
/*falseArgs=*/ArrayRef<Value>());
// Ok, we're done!
rewriter.replaceOp(ifOp, continueBlock->getArguments());
return success();
}
LogicalResult
ExecuteRegionLowering::matchAndRewrite(ExecuteRegionOp op,
PatternRewriter &rewriter) const {
auto loc = op.getLoc();
auto *condBlock = rewriter.getInsertionBlock();
auto opPosition = rewriter.getInsertionPoint();
auto *remainingOpsBlock = rewriter.splitBlock(condBlock, opPosition);
auto ®ion = op.getRegion();
rewriter.setInsertionPointToEnd(condBlock);
cf::BranchOp::create(rewriter, loc, ®ion.front());
for (Block &block : region) {
if (auto terminator = dyn_cast<scf::YieldOp>(block.getTerminator())) {
ValueRange terminatorOperands = terminator->getOperands();
rewriter.setInsertionPointToEnd(&block);
cf::BranchOp::create(rewriter, loc, remainingOpsBlock,
terminatorOperands);
rewriter.eraseOp(terminator);
}
}
rewriter.inlineRegionBefore(region, remainingOpsBlock);
SmallVector<Value> vals;
SmallVector<Location> argLocs(op.getNumResults(), op->getLoc());
for (auto arg :
remainingOpsBlock->addArguments(op->getResultTypes(), argLocs))
vals.push_back(arg);
rewriter.replaceOp(op, vals);
return success();
}
LogicalResult
ParallelLowering::matchAndRewrite(ParallelOp parallelOp,
PatternRewriter &rewriter) const {
Location loc = parallelOp.getLoc();
auto reductionOp = dyn_cast<ReduceOp>(parallelOp.getBody()->getTerminator());
if (!reductionOp) {
return failure();
}
// For a parallel loop, we essentially need to create an n-dimensional loop
// nest. We do this by translating to scf.for ops and have those lowered in
// a further rewrite. If a parallel loop contains reductions (and thus returns
// values), forward the initial values for the reductions down the loop
// hierarchy and bubble up the results by modifying the "yield" terminator.
SmallVector<Value, 4> iterArgs = llvm::to_vector<4>(parallelOp.getInitVals());
SmallVector<Value, 4> ivs;
ivs.reserve(parallelOp.getNumLoops());
bool first = true;
SmallVector<Value, 4> loopResults(iterArgs);
for (auto [iv, lower, upper, step] :
llvm::zip(parallelOp.getInductionVars(), parallelOp.getLowerBound(),
parallelOp.getUpperBound(), parallelOp.getStep())) {
ForOp forOp = ForOp::create(rewriter, loc, lower, upper, step, iterArgs);
ivs.push_back(forOp.getInductionVar());
auto iterRange = forOp.getRegionIterArgs();
iterArgs.assign(iterRange.begin(), iterRange.end());
if (first) {
// Store the results of the outermost loop that will be used to replace
// the results of the parallel loop when it is fully rewritten.
loopResults.assign(forOp.result_begin(), forOp.result_end());
first = false;
} else if (!forOp.getResults().empty()) {
// A loop is constructed with an empty "yield" terminator if there are
// no results.
rewriter.setInsertionPointToEnd(rewriter.getInsertionBlock());
scf::YieldOp::create(rewriter, loc, forOp.getResults());
}
rewriter.setInsertionPointToStart(forOp.getBody());
}
// First, merge reduction blocks into the main region.
SmallVector<Value> yieldOperands;
yieldOperands.reserve(parallelOp.getNumResults());
for (int64_t i = 0, e = parallelOp.getNumResults(); i < e; ++i) {
Block &reductionBody = reductionOp.getReductions()[i].front();
Value arg = iterArgs[yieldOperands.size()];
yieldOperands.push_back(
cast<ReduceReturnOp>(reductionBody.getTerminator()).getResult());
rewriter.eraseOp(reductionBody.getTerminator());
rewriter.inlineBlockBefore(&reductionBody, reductionOp,
{arg, reductionOp.getOperands()[i]});
}
rewriter.eraseOp(reductionOp);
// Then merge the loop body without the terminator.
Block *newBody = rewriter.getInsertionBlock();
if (newBody->empty())
rewriter.mergeBlocks(parallelOp.getBody(), newBody, ivs);
else
rewriter.inlineBlockBefore(parallelOp.getBody(), newBody->getTerminator(),
ivs);
// Finally, create the terminator if required (for loops with no results, it
// has been already created in loop construction).
if (!yieldOperands.empty()) {
rewriter.setInsertionPointToEnd(rewriter.getInsertionBlock());
scf::YieldOp::create(rewriter, loc, yieldOperands);
}
rewriter.replaceOp(parallelOp, loopResults);
return success();
}
LogicalResult WhileLowering::matchAndRewrite(WhileOp whileOp,
PatternRewriter &rewriter) const {
OpBuilder::InsertionGuard guard(rewriter);
Location loc = whileOp.getLoc();
// Split the current block before the WhileOp to create the inlining point.
Block *currentBlock = rewriter.getInsertionBlock();
Block *continuation =
rewriter.splitBlock(currentBlock, rewriter.getInsertionPoint());
// Inline both regions.
Block *after = whileOp.getAfterBody();
Block *before = whileOp.getBeforeBody();
rewriter.inlineRegionBefore(whileOp.getAfter(), continuation);
rewriter.inlineRegionBefore(whileOp.getBefore(), after);
// Branch to the "before" region.
rewriter.setInsertionPointToEnd(currentBlock);
cf::BranchOp::create(rewriter, loc, before, whileOp.getInits());
// Replace terminators with branches. Assuming bodies are SESE, which holds
// given only the patterns from this file, we only need to look at the last
// block. This should be reconsidered if we allow break/continue in SCF.
rewriter.setInsertionPointToEnd(before);
auto condOp = cast<ConditionOp>(before->getTerminator());
SmallVector<Value> args = llvm::to_vector(condOp.getArgs());
rewriter.replaceOpWithNewOp<cf::CondBranchOp>(condOp, condOp.getCondition(),
after, condOp.getArgs(),
continuation, ValueRange());
rewriter.setInsertionPointToEnd(after);
auto yieldOp = cast<scf::YieldOp>(after->getTerminator());
rewriter.replaceOpWithNewOp<cf::BranchOp>(yieldOp, before,
yieldOp.getResults());
// Replace the op with values "yielded" from the "before" region, which are
// visible by dominance.
rewriter.replaceOp(whileOp, args);
return success();
}
LogicalResult
DoWhileLowering::matchAndRewrite(WhileOp whileOp,
PatternRewriter &rewriter) const {
Block &afterBlock = *whileOp.getAfterBody();
if (!llvm::hasSingleElement(afterBlock))
return rewriter.notifyMatchFailure(whileOp,
"do-while simplification applicable "
"only if 'after' region has no payload");
auto yield = dyn_cast<scf::YieldOp>(&afterBlock.front());
if (!yield || yield.getResults() != afterBlock.getArguments())
return rewriter.notifyMatchFailure(whileOp,
"do-while simplification applicable "
"only to forwarding 'after' regions");
// Split the current block before the WhileOp to create the inlining point.
OpBuilder::InsertionGuard guard(rewriter);
Block *currentBlock = rewriter.getInsertionBlock();
Block *continuation =
rewriter.splitBlock(currentBlock, rewriter.getInsertionPoint());
// Only the "before" region should be inlined.
Block *before = whileOp.getBeforeBody();
rewriter.inlineRegionBefore(whileOp.getBefore(), continuation);
// Branch to the "before" region.
rewriter.setInsertionPointToEnd(currentBlock);
cf::BranchOp::create(rewriter, whileOp.getLoc(), before, whileOp.getInits());
// Loop around the "before" region based on condition.
rewriter.setInsertionPointToEnd(before);
auto condOp = cast<ConditionOp>(before->getTerminator());
cf::CondBranchOp::create(rewriter, condOp.getLoc(), condOp.getCondition(),
before, condOp.getArgs(), continuation,
ValueRange());
// Replace the op with values "yielded" from the "before" region, which are
// visible by dominance.
rewriter.replaceOp(whileOp, condOp.getArgs());
// Erase the condition op.
rewriter.eraseOp(condOp);
return success();
}
LogicalResult
IndexSwitchLowering::matchAndRewrite(IndexSwitchOp op,
PatternRewriter &rewriter) const {
// Split the block at the op.
Block *condBlock = rewriter.getInsertionBlock();
Block *continueBlock = rewriter.splitBlock(condBlock, Block::iterator(op));
// Create the arguments on the continue block with which to replace the
// results of the op.
SmallVector<Value> results;
results.reserve(op.getNumResults());
for (Type resultType : op.getResultTypes())
results.push_back(continueBlock->addArgument(resultType, op.getLoc()));
// Handle the regions.
auto convertRegion = [&](Region ®ion) -> FailureOr<Block *> {
Block *block = ®ion.front();
// Convert the yield terminator to a branch to the continue block.
auto yield = cast<scf::YieldOp>(block->getTerminator());
rewriter.setInsertionPoint(yield);
rewriter.replaceOpWithNewOp<cf::BranchOp>(yield, continueBlock,
yield.getOperands());
// Inline the region.
rewriter.inlineRegionBefore(region, continueBlock);
return block;
};
// Convert the case regions.
SmallVector<Block *> caseSuccessors;
SmallVector<int32_t> caseValues;
caseSuccessors.reserve(op.getCases().size());
caseValues.reserve(op.getCases().size());
for (auto [region, value] : llvm::zip(op.getCaseRegions(), op.getCases())) {
FailureOr<Block *> block = convertRegion(region);
if (failed(block))
return failure();
caseSuccessors.push_back(*block);
caseValues.push_back(value);
}
// Convert the default region.
FailureOr<Block *> defaultBlock = convertRegion(op.getDefaultRegion());
if (failed(defaultBlock))
return failure();
// Create the switch.
rewriter.setInsertionPointToEnd(condBlock);
SmallVector<ValueRange> caseOperands(caseSuccessors.size(), {});
// Cast switch index to integer case value.
Value caseValue = arith::IndexCastOp::create(
rewriter, op.getLoc(), rewriter.getI32Type(), op.getArg());
cf::SwitchOp::create(rewriter, op.getLoc(), caseValue, *defaultBlock,
ValueRange(), rewriter.getDenseI32ArrayAttr(caseValues),
caseSuccessors, caseOperands);
rewriter.replaceOp(op, continueBlock->getArguments());
return success();
}
LogicalResult ForallLowering::matchAndRewrite(ForallOp forallOp,
PatternRewriter &rewriter) const {
return scf::forallToParallelLoop(rewriter, forallOp);
}
void mlir::populateSCFToControlFlowConversionPatterns(
RewritePatternSet &patterns) {
patterns.add<ForallLowering, ForLowering, IfLowering, ParallelLowering,
WhileLowering, ExecuteRegionLowering, IndexSwitchLowering>(
patterns.getContext());
patterns.add<DoWhileLowering>(patterns.getContext(), /*benefit=*/2);
}
void SCFToControlFlowPass::runOnOperation() {
RewritePatternSet patterns(&getContext());
populateSCFToControlFlowConversionPatterns(patterns);
// Configure conversion to lower out SCF operations.
ConversionTarget target(getContext());
target.addIllegalOp<scf::ForallOp, scf::ForOp, scf::IfOp, scf::IndexSwitchOp,
scf::ParallelOp, scf::WhileOp, scf::ExecuteRegionOp>();
target.markUnknownOpDynamicallyLegal([](Operation *) { return true; });
if (failed(
applyPartialConversion(getOperation(), target, std::move(patterns))))
signalPassFailure();
}
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