1 //===-- FuncletLayout.cpp - Contiguously lay out funclets -----------------===//
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 // This file implements basic block placement transformations which result in
10 // funclets being contiguous.
11 //
12 //===----------------------------------------------------------------------===//
13 #include "llvm/CodeGen/Analysis.h"
14 #include "llvm/CodeGen/MachineFunction.h"
15 #include "llvm/CodeGen/MachineFunctionPass.h"
16 #include "llvm/CodeGen/Passes.h"
17 #include "llvm/InitializePasses.h"
18 using namespace llvm;
19 
20 #define DEBUG_TYPE "funclet-layout"
21 
22 namespace {
23 class FuncletLayout : public MachineFunctionPass {
24 public:
25   static char ID; // Pass identification, replacement for typeid
FuncletLayout()26   FuncletLayout() : MachineFunctionPass(ID) {
27     initializeFuncletLayoutPass(*PassRegistry::getPassRegistry());
28   }
29 
30   bool runOnMachineFunction(MachineFunction &F) override;
getRequiredProperties() const31   MachineFunctionProperties getRequiredProperties() const override {
32     return MachineFunctionProperties().set(
33         MachineFunctionProperties::Property::NoVRegs);
34   }
35 };
36 }
37 
38 char FuncletLayout::ID = 0;
39 char &llvm::FuncletLayoutID = FuncletLayout::ID;
40 INITIALIZE_PASS(FuncletLayout, DEBUG_TYPE,
41                 "Contiguously Lay Out Funclets", false, false)
42 
runOnMachineFunction(MachineFunction & F)43 bool FuncletLayout::runOnMachineFunction(MachineFunction &F) {
44   // Even though this gets information from getEHScopeMembership(), this pass is
45   // only necessary for funclet-based EH personalities, in which these EH scopes
46   // are outlined at the end.
47   DenseMap<const MachineBasicBlock *, int> FuncletMembership =
48       getEHScopeMembership(F);
49   if (FuncletMembership.empty())
50     return false;
51 
52   F.sort([&](MachineBasicBlock &X, MachineBasicBlock &Y) {
53     auto FuncletX = FuncletMembership.find(&X);
54     auto FuncletY = FuncletMembership.find(&Y);
55     assert(FuncletX != FuncletMembership.end());
56     assert(FuncletY != FuncletMembership.end());
57     return FuncletX->second < FuncletY->second;
58   });
59 
60   // Conservatively assume we changed something.
61   return true;
62 }
63