1 //===- LegalizeForExport.cpp - Prepare for translation to LLVM IR ---------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include "mlir/Dialect/LLVMIR/Transforms/LegalizeForExport.h"
10
11 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
12 #include "mlir/Dialect/LLVMIR/Transforms/DIExpressionLegalization.h"
13 #include "mlir/IR/Block.h"
14 #include "mlir/IR/Builders.h"
15 #include "mlir/IR/BuiltinOps.h"
16 #include "mlir/Pass/Pass.h"
17
18 namespace mlir {
19 namespace LLVM {
20 #define GEN_PASS_DEF_LLVMLEGALIZEFOREXPORT
21 #include "mlir/Dialect/LLVMIR/Transforms/Passes.h.inc"
22 } // namespace LLVM
23 } // namespace mlir
24
25 using namespace mlir;
26
27 /// If the given block has the same successor with different arguments,
28 /// introduce dummy successor blocks so that all successors of the given block
29 /// are different.
ensureDistinctSuccessors(Block & bb)30 static void ensureDistinctSuccessors(Block &bb) {
31 // Early exit if the block cannot have successors.
32 if (bb.empty() || !bb.back().mightHaveTrait<OpTrait::IsTerminator>())
33 return;
34
35 auto *terminator = bb.getTerminator();
36
37 // Find repeated successors with arguments.
38 llvm::SmallDenseMap<Block *, SmallVector<int, 4>> successorPositions;
39 for (int i = 0, e = terminator->getNumSuccessors(); i < e; ++i) {
40 Block *successor = terminator->getSuccessor(i);
41 // Blocks with no arguments are safe even if they appear multiple times
42 // because they don't need PHI nodes.
43 if (successor->getNumArguments() == 0)
44 continue;
45 successorPositions[successor].push_back(i);
46 }
47
48 // If a successor appears for the second or more time in the terminator,
49 // create a new dummy block that unconditionally branches to the original
50 // destination, and retarget the terminator to branch to this new block.
51 // There is no need to pass arguments to the dummy block because it will be
52 // dominated by the original block and can therefore use any values defined in
53 // the original block.
54 OpBuilder builder(terminator->getContext());
55 for (const auto &successor : successorPositions) {
56 // Start from the second occurrence of a block in the successor list.
57 for (int position : llvm::drop_begin(successor.second, 1)) {
58 Block *dummyBlock = builder.createBlock(bb.getParent());
59 terminator->setSuccessor(dummyBlock, position);
60 for (BlockArgument arg : successor.first->getArguments())
61 dummyBlock->addArgument(arg.getType(), arg.getLoc());
62 builder.create<LLVM::BrOp>(terminator->getLoc(),
63 dummyBlock->getArguments(), successor.first);
64 }
65 }
66 }
67
ensureDistinctSuccessors(Operation * op)68 void mlir::LLVM::ensureDistinctSuccessors(Operation *op) {
69 op->walk([](Operation *nested) {
70 for (Region ®ion : llvm::make_early_inc_range(nested->getRegions())) {
71 for (Block &block : llvm::make_early_inc_range(region)) {
72 ::ensureDistinctSuccessors(block);
73 }
74 }
75 });
76 }
77
78 namespace {
79 struct LegalizeForExportPass
80 : public LLVM::impl::LLVMLegalizeForExportBase<LegalizeForExportPass> {
runOnOperation__anon41e5471a0211::LegalizeForExportPass81 void runOnOperation() override {
82 LLVM::ensureDistinctSuccessors(getOperation());
83 LLVM::legalizeDIExpressionsRecursively(getOperation());
84 }
85 };
86 } // namespace
87
createLegalizeForExportPass()88 std::unique_ptr<Pass> LLVM::createLegalizeForExportPass() {
89 return std::make_unique<LegalizeForExportPass>();
90 }
91