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 #include "PassDetail.h"
11 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
12 #include "mlir/IR/Block.h"
13 #include "mlir/IR/Builders.h"
14 #include "mlir/IR/BuiltinOps.h"
15
16 using namespace mlir;
17
ensureDistinctSuccessors(Block & bb)18 static void ensureDistinctSuccessors(Block &bb) {
19 auto *terminator = bb.getTerminator();
20
21 // Find repeated successors with arguments.
22 llvm::SmallDenseMap<Block *, SmallVector<int, 4>> successorPositions;
23 for (int i = 0, e = terminator->getNumSuccessors(); i < e; ++i) {
24 Block *successor = terminator->getSuccessor(i);
25 // Blocks with no arguments are safe even if they appear multiple times
26 // because they don't need PHI nodes.
27 if (successor->getNumArguments() == 0)
28 continue;
29 successorPositions[successor].push_back(i);
30 }
31
32 // If a successor appears for the second or more time in the terminator,
33 // create a new dummy block that unconditionally branches to the original
34 // destination, and retarget the terminator to branch to this new block.
35 // There is no need to pass arguments to the dummy block because it will be
36 // dominated by the original block and can therefore use any values defined in
37 // the original block.
38 OpBuilder builder(terminator->getContext());
39 for (const auto &successor : successorPositions) {
40 // Start from the second occurrence of a block in the successor list.
41 for (int position : llvm::drop_begin(successor.second, 1)) {
42 Block *dummyBlock = builder.createBlock(bb.getParent());
43 terminator->setSuccessor(dummyBlock, position);
44 dummyBlock->addArguments(successor.first->getArgumentTypes());
45 builder.create<LLVM::BrOp>(terminator->getLoc(),
46 dummyBlock->getArguments(), successor.first);
47 }
48 }
49 }
50
ensureDistinctSuccessors(Operation * op)51 void mlir::LLVM::ensureDistinctSuccessors(Operation *op) {
52 op->walk([](LLVMFuncOp f) {
53 for (auto &bb : f) {
54 ::ensureDistinctSuccessors(bb);
55 }
56 });
57 }
58
59 namespace {
60 struct LegalizeForExportPass
61 : public LLVMLegalizeForExportBase<LegalizeForExportPass> {
runOnOperation__anona2ba9db70211::LegalizeForExportPass62 void runOnOperation() override {
63 LLVM::ensureDistinctSuccessors(getOperation());
64 }
65 };
66 } // end namespace
67
createLegalizeForExportPass()68 std::unique_ptr<Pass> LLVM::createLegalizeForExportPass() {
69 return std::make_unique<LegalizeForExportPass>();
70 }
71