1 //===-- WebAssemblyArgumentMove.cpp - Argument instruction moving ---------===// 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 /// \file 10 /// This file moves ARGUMENT instructions after ScheduleDAG scheduling. 11 /// 12 /// Arguments are really live-in registers, however, since we use virtual 13 /// registers and LLVM doesn't support live-in virtual registers, we're 14 /// currently making do with ARGUMENT instructions which are placed at the top 15 /// of the entry block. The trick is to get them to *stay* at the top of the 16 /// entry block. 17 /// 18 /// The ARGUMENTS physical register keeps these instructions pinned in place 19 /// during liveness-aware CodeGen passes, however one thing which does not 20 /// respect this is the ScheduleDAG scheduler. This pass is therefore run 21 /// immediately after that. 22 /// 23 /// This is all hopefully a temporary solution until we find a better solution 24 /// for describing the live-in nature of arguments. 25 /// 26 //===----------------------------------------------------------------------===// 27 28 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h" 29 #include "WebAssembly.h" 30 #include "WebAssemblyUtilities.h" 31 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" 32 #include "llvm/CodeGen/Passes.h" 33 #include "llvm/Support/Debug.h" 34 #include "llvm/Support/raw_ostream.h" 35 using namespace llvm; 36 37 #define DEBUG_TYPE "wasm-argument-move" 38 39 namespace { 40 class WebAssemblyArgumentMove final : public MachineFunctionPass { 41 public: 42 static char ID; // Pass identification, replacement for typeid 43 WebAssemblyArgumentMove() : MachineFunctionPass(ID) {} 44 45 StringRef getPassName() const override { return "WebAssembly Argument Move"; } 46 47 void getAnalysisUsage(AnalysisUsage &AU) const override { 48 AU.setPreservesCFG(); 49 AU.addPreserved<MachineBlockFrequencyInfoWrapperPass>(); 50 AU.addPreservedID(MachineDominatorsID); 51 MachineFunctionPass::getAnalysisUsage(AU); 52 } 53 54 bool runOnMachineFunction(MachineFunction &MF) override; 55 }; 56 } // end anonymous namespace 57 58 char WebAssemblyArgumentMove::ID = 0; 59 INITIALIZE_PASS(WebAssemblyArgumentMove, DEBUG_TYPE, 60 "Move ARGUMENT instructions for WebAssembly", false, false) 61 62 FunctionPass *llvm::createWebAssemblyArgumentMove() { 63 return new WebAssemblyArgumentMove(); 64 } 65 66 bool WebAssemblyArgumentMove::runOnMachineFunction(MachineFunction &MF) { 67 LLVM_DEBUG({ 68 dbgs() << "********** Argument Move **********\n" 69 << "********** Function: " << MF.getName() << '\n'; 70 }); 71 72 bool Changed = false; 73 MachineBasicBlock &EntryMBB = MF.front(); 74 MachineBasicBlock::iterator InsertPt = EntryMBB.end(); 75 76 // Look for the first NonArg instruction. 77 for (MachineInstr &MI : EntryMBB) { 78 if (!WebAssembly::isArgument(MI.getOpcode())) { 79 InsertPt = MI; 80 break; 81 } 82 } 83 84 // Now move any argument instructions later in the block 85 // to before our first NonArg instruction. 86 for (MachineInstr &MI : llvm::make_range(InsertPt, EntryMBB.end())) { 87 if (WebAssembly::isArgument(MI.getOpcode())) { 88 EntryMBB.insert(InsertPt, MI.removeFromParent()); 89 Changed = true; 90 } 91 } 92 93 return Changed; 94 } 95