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 "WebAssemblyMachineFunctionInfo.h" 31 #include "WebAssemblySubtarget.h" 32 #include "WebAssemblyUtilities.h" 33 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" 34 #include "llvm/CodeGen/MachineRegisterInfo.h" 35 #include "llvm/CodeGen/Passes.h" 36 #include "llvm/Support/Debug.h" 37 #include "llvm/Support/raw_ostream.h" 38 using namespace llvm; 39 40 #define DEBUG_TYPE "wasm-argument-move" 41 42 namespace { 43 class WebAssemblyArgumentMove final : public MachineFunctionPass { 44 public: 45 static char ID; // Pass identification, replacement for typeid 46 WebAssemblyArgumentMove() : MachineFunctionPass(ID) {} 47 48 StringRef getPassName() const override { return "WebAssembly Argument Move"; } 49 50 void getAnalysisUsage(AnalysisUsage &AU) const override { 51 AU.setPreservesCFG(); 52 AU.addPreserved<MachineBlockFrequencyInfo>(); 53 AU.addPreservedID(MachineDominatorsID); 54 MachineFunctionPass::getAnalysisUsage(AU); 55 } 56 57 bool runOnMachineFunction(MachineFunction &MF) override; 58 }; 59 } // end anonymous namespace 60 61 char WebAssemblyArgumentMove::ID = 0; 62 INITIALIZE_PASS(WebAssemblyArgumentMove, DEBUG_TYPE, 63 "Move ARGUMENT instructions for WebAssembly", false, false) 64 65 FunctionPass *llvm::createWebAssemblyArgumentMove() { 66 return new WebAssemblyArgumentMove(); 67 } 68 69 bool WebAssemblyArgumentMove::runOnMachineFunction(MachineFunction &MF) { 70 LLVM_DEBUG({ 71 dbgs() << "********** Argument Move **********\n" 72 << "********** Function: " << MF.getName() << '\n'; 73 }); 74 75 bool Changed = false; 76 MachineBasicBlock &EntryMBB = MF.front(); 77 MachineBasicBlock::iterator InsertPt = EntryMBB.end(); 78 79 // Look for the first NonArg instruction. 80 for (MachineInstr &MI : EntryMBB) { 81 if (!WebAssembly::isArgument(MI.getOpcode())) { 82 InsertPt = MI; 83 break; 84 } 85 } 86 87 // Now move any argument instructions later in the block 88 // to before our first NonArg instruction. 89 for (MachineInstr &MI : llvm::make_range(InsertPt, EntryMBB.end())) { 90 if (WebAssembly::isArgument(MI.getOpcode())) { 91 EntryMBB.insert(InsertPt, MI.removeFromParent()); 92 Changed = true; 93 } 94 } 95 96 return Changed; 97 } 98