1 //===-- WebAssemblyArgumentMove.cpp - Argument instruction moving ---------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 /// 10 /// \file 11 /// This file moves ARGUMENT instructions after ScheduleDAG scheduling. 12 /// 13 /// Arguments are really live-in registers, however, since we use virtual 14 /// registers and LLVM doesn't support live-in virtual registers, we're 15 /// currently making do with ARGUMENT instructions which are placed at the top 16 /// of the entry block. The trick is to get them to *stay* at the top of the 17 /// entry block. 18 /// 19 /// The ARGUMENTS physical register keeps these instructions pinned in place 20 /// during liveness-aware CodeGen passes, however one thing which does not 21 /// respect this is the ScheduleDAG scheduler. This pass is therefore run 22 /// immediately after that. 23 /// 24 /// This is all hopefully a temporary solution until we find a better solution 25 /// for describing the live-in nature of arguments. 26 /// 27 //===----------------------------------------------------------------------===// 28 29 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h" 30 #include "WebAssembly.h" 31 #include "WebAssemblyMachineFunctionInfo.h" 32 #include "WebAssemblySubtarget.h" 33 #include "WebAssemblyUtilities.h" 34 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" 35 #include "llvm/CodeGen/MachineRegisterInfo.h" 36 #include "llvm/CodeGen/Passes.h" 37 #include "llvm/Support/Debug.h" 38 #include "llvm/Support/raw_ostream.h" 39 using namespace llvm; 40 41 #define DEBUG_TYPE "wasm-argument-move" 42 43 namespace { 44 class WebAssemblyArgumentMove final : public MachineFunctionPass { 45 public: 46 static char ID; // Pass identification, replacement for typeid 47 WebAssemblyArgumentMove() : MachineFunctionPass(ID) {} 48 49 StringRef getPassName() const override { return "WebAssembly Argument Move"; } 50 51 void getAnalysisUsage(AnalysisUsage &AU) const override { 52 AU.setPreservesCFG(); 53 AU.addPreserved<MachineBlockFrequencyInfo>(); 54 AU.addPreservedID(MachineDominatorsID); 55 MachineFunctionPass::getAnalysisUsage(AU); 56 } 57 58 bool runOnMachineFunction(MachineFunction &MF) override; 59 }; 60 } // end anonymous namespace 61 62 char WebAssemblyArgumentMove::ID = 0; 63 INITIALIZE_PASS(WebAssemblyArgumentMove, DEBUG_TYPE, 64 "Move ARGUMENT instructions for WebAssembly", false, false) 65 66 FunctionPass *llvm::createWebAssemblyArgumentMove() { 67 return new WebAssemblyArgumentMove(); 68 } 69 70 bool WebAssemblyArgumentMove::runOnMachineFunction(MachineFunction &MF) { 71 LLVM_DEBUG({ 72 dbgs() << "********** Argument Move **********\n" 73 << "********** Function: " << MF.getName() << '\n'; 74 }); 75 76 bool Changed = false; 77 MachineBasicBlock &EntryMBB = MF.front(); 78 MachineBasicBlock::iterator InsertPt = EntryMBB.end(); 79 80 // Look for the first NonArg instruction. 81 for (MachineInstr &MI : EntryMBB) { 82 if (!WebAssembly::isArgument(MI)) { 83 InsertPt = MI; 84 break; 85 } 86 } 87 88 // Now move any argument instructions later in the block 89 // to before our first NonArg instruction. 90 for (MachineInstr &MI : llvm::make_range(InsertPt, EntryMBB.end())) { 91 if (WebAssembly::isArgument(MI)) { 92 EntryMBB.insert(InsertPt, MI.removeFromParent()); 93 Changed = true; 94 } 95 } 96 97 return Changed; 98 } 99
