doxygen/SCFToControlFlow_8cpp_source.html

 //===- 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


 static void propagateLoopAttrs(Operation *scfOp, Operation *brOp) {

   // 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(scfOp->getAttrs(), std::back_inserter(llvmAttrs),

                 [](auto attr) {

                   return isa<LLVM::LLVMDialect>(attr.getValue().getDialect());

                 });

   brOp->setDiscardableAttrs(llvmAttrs);

 }


 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);


   propagateLoopAttrs(forOp, branchOp);

   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);

   arith::CmpIPredicate predicate = forOp.getUnsignedCmp()

                                        ? arith::CmpIPredicate::ult

                                        : arith::CmpIPredicate::slt;

   auto comparison =

       arith::CmpIOp::create(rewriter, loc, predicate, 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 &region = op.getRegion();

   rewriter.setInsertionPointToEnd(condBlock);

   cf::BranchOp::create(rewriter, loc, &region.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());

   auto latch = rewriter.replaceOpWithNewOp<cf::BranchOp>(yieldOp, before,

                                                          yieldOp.getResults());


   propagateLoopAttrs(whileOp, latch);

   // 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());

   auto latch = cf::CondBranchOp::create(

       rewriter, condOp.getLoc(), condOp.getCondition(), before,

       condOp.getArgs(), continuation, ValueRange());


   propagateLoopAttrs(whileOp, latch);

   // 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 &region) -> FailureOr<Block *> {

     Block *block = &region.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();

 }

Builders.h

ControlFlowOps.h

DialectConversion.h

getContext
static MLIRContext * getContext(OpFoldResult val)
Definition: IndexingUtils.cpp:296

LLVMDialect.h

MLIRContext.h

PatternMatch.h

propagateLoopAttrs
static void propagateLoopAttrs(Operation *scfOp, Operation *brOp)
Definition: SCFToControlFlow.cpp:315

SCFToControlFlow.h

Passes.h

llvm::ArrayRef
Definition: LLVM.h:48

llvm::SmallVector
Definition: LLVM.h:72

mlir::Block
Block represents an ordered list of Operations.
Definition: Block.h:33

mlir::Block::iterator
OpListType::iterator iterator
Definition: Block.h:140

mlir::Block::empty
bool empty()
Definition: Block.h:148

mlir::Block::back
Operation & back()
Definition: Block.h:152

mlir::Block::getTerminator
Operation * getTerminator()
Get the terminator operation of this block.
Definition: Block.cpp:244

mlir::Block::addArgument
BlockArgument addArgument(Type type, Location loc)
Add one value to the argument list.
Definition: Block.cpp:153

mlir::Block::getArguments
BlockArgListType getArguments()
Definition: Block.h:87

mlir::Block::front
Operation & front()
Definition: Block.h:153

mlir::Builder::getDenseI32ArrayAttr
DenseI32ArrayAttr getDenseI32ArrayAttr(ArrayRef< int32_t > values)
Definition: Builders.cpp:162

mlir::Builder::getI32Type
IntegerType getI32Type()
Definition: Builders.cpp:62

mlir::ConversionTarget
This class describes a specific conversion target.
Definition: DialectConversion.h:1034

mlir::Location
This class defines the main interface for locations in MLIR and acts as a non-nullable wrapper around...
Definition: Location.h:76

mlir::OpBuilder::InsertionGuard
RAII guard to reset the insertion point of the builder when destroyed.
Definition: Builders.h:348

mlir::OpBuilder::getInsertionPoint
Block::iterator getInsertionPoint() const
Returns the current insertion point of the builder.
Definition: Builders.h:445

mlir::OpBuilder::createBlock
Block * createBlock(Region *parent, Region::iterator insertPt={}, TypeRange argTypes={}, ArrayRef< Location > locs={})
Add new block with 'argTypes' arguments and set the insertion point to the end of it.
Definition: Builders.cpp:429

mlir::OpBuilder::setInsertionPointToStart
void setInsertionPointToStart(Block *block)
Sets the insertion point to the start of the specified block.
Definition: Builders.h:431

mlir::OpBuilder::setInsertionPoint
void setInsertionPoint(Block *block, Block::iterator insertPoint)
Set the insertion point to the specified location.
Definition: Builders.h:398

mlir::OpBuilder::setInsertionPointToEnd
void setInsertionPointToEnd(Block *block)
Sets the insertion point to the end of the specified block.
Definition: Builders.h:436

mlir::OpBuilder::getInsertionBlock
Block * getInsertionBlock() const
Return the block the current insertion point belongs to.
Definition: Builders.h:442

mlir::Operation
Operation is the basic unit of execution within MLIR.
Definition: Operation.h:88

mlir::Operation::operand_begin
operand_iterator operand_begin()
Definition: Operation.h:374

mlir::Operation::getAttrs
ArrayRef< NamedAttribute > getAttrs()
Return all of the attributes on this operation.
Definition: Operation.h:512

mlir::Operation::operand_end
operand_iterator operand_end()
Definition: Operation.h:375

mlir::Operation::getOperands
operand_range getOperands()
Returns an iterator on the underlying Value's.
Definition: Operation.h:378

mlir::Operation::setDiscardableAttrs
void setDiscardableAttrs(DictionaryAttr newAttrs)
Set the discardable attribute dictionary on this operation.
Definition: Operation.h:523

mlir::PatternRewriter
A special type of RewriterBase that coordinates the application of a rewrite pattern on the current I...
Definition: PatternMatch.h:793

mlir::Region
This class contains a list of basic blocks and a link to the parent operation it is attached to.
Definition: Region.h:26

mlir::RewritePatternSet
Definition: PatternMatch.h:816

mlir::RewriterBase::notifyMatchFailure
std::enable_if_t<!std::is_convertible< CallbackT, Twine >::value, LogicalResult > notifyMatchFailure(Location loc, CallbackT &&reasonCallback)
Used to notify the listener that the IR failed to be rewritten because of a match failure,...
Definition: PatternMatch.h:726

mlir::RewriterBase::splitBlock
Block * splitBlock(Block *block, Block::iterator before)
Split the operations starting at "before" (inclusive) out of the given block into a new block,...
Definition: PatternMatch.cpp:350

mlir::RewriterBase::replaceOp
virtual void replaceOp(Operation *op, ValueRange newValues)
Replace the results of the given (original) operation with the specified list of values (replacements...
Definition: PatternMatch.cpp:127

mlir::RewriterBase::eraseOp
virtual void eraseOp(Operation *op)
This method erases an operation that is known to have no uses.
Definition: PatternMatch.cpp:155

mlir::RewriterBase::inlineBlockBefore
virtual void inlineBlockBefore(Block *source, Block *dest, Block::iterator before, ValueRange argValues={})
Inline the operations of block 'source' into block 'dest' before the given position.
Definition: PatternMatch.cpp:290

mlir::RewriterBase::mergeBlocks
void mergeBlocks(Block *source, Block *dest, ValueRange argValues={})
Inline the operations of block 'source' into the end of block 'dest'.
Definition: PatternMatch.cpp:343

mlir::RewriterBase::inlineRegionBefore
void inlineRegionBefore(Region &region, Region &parent, Region::iterator before)
Move the blocks that belong to "region" before the given position in another region "parent".
Definition: PatternMatch.cpp:376

mlir::RewriterBase::replaceOpWithNewOp
OpTy replaceOpWithNewOp(Operation *op, Args &&...args)
Replace the results of the given (original) op with a new op that is created without verification (re...
Definition: PatternMatch.h:529

mlir::Type
Instances of the Type class are uniqued, have an immutable identifier and an optional mutable compone...
Definition: Types.h:74

mlir::ValueRange
This class provides an abstraction over the different types of ranges over Values.
Definition: ValueRange.h:387

mlir::Value
This class represents an instance of an SSA value in the MLIR system, representing a computable value...
Definition: Value.h:96

Arith.h

SCF.h

Transforms.h

mlir::remark::failed
detail::InFlightRemark failed(Location loc, RemarkOpts opts)
Report an optimization remark that failed.
Definition: Remarks.h:491

mlir::scf
Definition: SCFToGPU.h:24

mlir::scf::forallToParallelLoop
LogicalResult forallToParallelLoop(RewriterBase &rewriter, ForallOp forallOp, ParallelOp *result=nullptr)
Try converting scf.forall into an scf.parallel loop.

mlir
Include the generated interface declarations.
Definition: LocalAliasAnalysis.h:20

mlir::patterns
const FrozenRewritePatternSet & patterns
Definition: GreedyPatternRewriteDriver.h:283

mlir::populateSCFToControlFlowConversionPatterns
void populateSCFToControlFlowConversionPatterns(RewritePatternSet &patterns)
Collect a set of patterns to convert SCF operations to CFG branch-based operations within the Control...
Definition: SCFToControlFlow.cpp:722

mlir::applyPartialConversion
LogicalResult applyPartialConversion(ArrayRef< Operation * > ops, const ConversionTarget &target, const FrozenRewritePatternSet &patterns, ConversionConfig config=ConversionConfig())
Below we define several entry points for operation conversion.
Definition: DialectConversion.cpp:4117

mlir::OpRewritePattern
OpRewritePattern is a wrapper around RewritePattern that allows for matching and rewriting against an...
Definition: PatternMatch.h:314

mlir::OpRewritePattern::OpRewritePattern
OpRewritePattern(MLIRContext *context, PatternBenefit benefit=1, ArrayRef< StringRef > generatedNames={})
Patterns must specify the root operation name they match against, and can also specify the benefit of...
Definition: PatternMatch.h:322