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      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
     26   FuncletLayout() : MachineFunctionPass(ID) {
     27     initializeFuncletLayoutPass(*PassRegistry::getPassRegistry());
     28   }
     29 
     30   bool runOnMachineFunction(MachineFunction &F) override;
     31   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 
     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