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//===- LegalizeForExport.cpp - Prepare for translation to LLVM IR ---------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "mlir/Dialect/LLVMIR/Transforms/LegalizeForExport.h"
#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
#include "mlir/IR/Block.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/BuiltinOps.h"
#include "mlir/Pass/Pass.h"
namespace mlir {
namespace LLVM {
#define GEN_PASS_DEF_LLVMLEGALIZEFOREXPORT
#include "mlir/Dialect/LLVMIR/Transforms/Passes.h.inc"
} // namespace LLVM
} // namespace mlir
using namespace mlir;
/// If the given block has the same successor with different arguments,
/// introduce dummy successor blocks so that all successors of the given block
/// are different.
static void ensureDistinctSuccessors(Block &bb) {
// Early exit if the block cannot have successors.
if (bb.empty() || !bb.back().mightHaveTrait<OpTrait::IsTerminator>())
return;
auto *terminator = bb.getTerminator();
// Find repeated successors with arguments.
llvm::SmallDenseMap<Block *, SmallVector<int, 4>> successorPositions;
for (int i = 0, e = terminator->getNumSuccessors(); i < e; ++i) {
Block *successor = terminator->getSuccessor(i);
// Blocks with no arguments are safe even if they appear multiple times
// because they don't need PHI nodes.
if (successor->getNumArguments() == 0)
continue;
successorPositions[successor].push_back(i);
}
// If a successor appears for the second or more time in the terminator,
// create a new dummy block that unconditionally branches to the original
// destination, and retarget the terminator to branch to this new block.
// There is no need to pass arguments to the dummy block because it will be
// dominated by the original block and can therefore use any values defined in
// the original block.
OpBuilder builder(terminator->getContext());
for (const auto &successor : successorPositions) {
// Start from the second occurrence of a block in the successor list.
for (int position : llvm::drop_begin(successor.second, 1)) {
Block *dummyBlock = builder.createBlock(bb.getParent());
terminator->setSuccessor(dummyBlock, position);
for (BlockArgument arg : successor.first->getArguments())
dummyBlock->addArgument(arg.getType(), arg.getLoc());
builder.create<LLVM::BrOp>(terminator->getLoc(),
dummyBlock->getArguments(), successor.first);
}
}
}
void mlir::LLVM::ensureDistinctSuccessors(Operation *op) {
op->walk([](Operation *nested) {
for (Region ®ion : llvm::make_early_inc_range(nested->getRegions())) {
for (Block &block : llvm::make_early_inc_range(region)) {
::ensureDistinctSuccessors(block);
}
}
});
}
namespace {
struct LegalizeForExportPass
: public LLVM::impl::LLVMLegalizeForExportBase<LegalizeForExportPass> {
void runOnOperation() override {
LLVM::ensureDistinctSuccessors(getOperation());
}
};
} // namespace
std::unique_ptr<Pass> LLVM::createLegalizeForExportPass() {
return std::make_unique<LegalizeForExportPass>();
}
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