1 //===- MipsMulMulBugPass.cpp - Mips VR4300 mulmul bugfix pass -------------===// 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 // Early revisions of the VR4300 have a hardware bug where two consecutive 10 // multiplications can produce an incorrect result in the second multiply. 11 // 12 // This pass scans for mul instructions in each basic block and inserts 13 // a nop whenever the following conditions are met: 14 // 15 // - The current instruction is a single or double-precision floating-point 16 // mul instruction. 17 // - The next instruction is either a mul instruction (any kind) 18 // or a branch instruction. 19 //===----------------------------------------------------------------------===// 20 21 #include "Mips.h" 22 #include "MipsInstrInfo.h" 23 #include "MipsSubtarget.h" 24 #include "llvm/CodeGen/MachineBasicBlock.h" 25 #include "llvm/CodeGen/MachineFunction.h" 26 #include "llvm/CodeGen/MachineFunctionPass.h" 27 #include "llvm/Support/Debug.h" 28 #include "llvm/Target/TargetMachine.h" 29 30 #define DEBUG_TYPE "mips-vr4300-mulmul-fix" 31 32 using namespace llvm; 33 34 namespace { 35 36 class MipsMulMulBugFix : public MachineFunctionPass { 37 public: 38 MipsMulMulBugFix() : MachineFunctionPass(ID) { 39 initializeMipsMulMulBugFixPass(*PassRegistry::getPassRegistry()); 40 } 41 42 StringRef getPassName() const override { return "Mips VR4300 mulmul bugfix"; } 43 44 MachineFunctionProperties getRequiredProperties() const override { 45 return MachineFunctionProperties().set( 46 MachineFunctionProperties::Property::NoVRegs); 47 } 48 49 bool runOnMachineFunction(MachineFunction &MF) override; 50 51 static char ID; 52 53 private: 54 bool fixMulMulBB(MachineBasicBlock &MBB, const MipsInstrInfo &MipsII); 55 }; 56 57 } // namespace 58 59 INITIALIZE_PASS(MipsMulMulBugFix, "mips-vr4300-mulmul-fix", 60 "Mips VR4300 mulmul bugfix", false, false) 61 62 char MipsMulMulBugFix::ID = 0; 63 64 bool MipsMulMulBugFix::runOnMachineFunction(MachineFunction &MF) { 65 const MipsInstrInfo &MipsII = 66 *static_cast<const MipsInstrInfo *>(MF.getSubtarget().getInstrInfo()); 67 68 bool Modified = false; 69 70 for (auto &MBB : MF) 71 Modified |= fixMulMulBB(MBB, MipsII); 72 73 return Modified; 74 } 75 76 static bool isFirstMul(const MachineInstr &MI) { 77 switch (MI.getOpcode()) { 78 case Mips::FMUL_S: 79 case Mips::FMUL_D: 80 case Mips::FMUL_D32: 81 case Mips::FMUL_D64: 82 return true; 83 default: 84 return false; 85 } 86 } 87 88 static bool isSecondMulOrBranch(const MachineInstr &MI) { 89 if (MI.isBranch() || MI.isIndirectBranch() || MI.isCall()) 90 return true; 91 92 switch (MI.getOpcode()) { 93 case Mips::MUL: 94 case Mips::FMUL_S: 95 case Mips::FMUL_D: 96 case Mips::FMUL_D32: 97 case Mips::FMUL_D64: 98 case Mips::MULT: 99 case Mips::MULTu: 100 case Mips::DMULT: 101 case Mips::DMULTu: 102 return true; 103 default: 104 return false; 105 } 106 } 107 108 bool MipsMulMulBugFix::fixMulMulBB(MachineBasicBlock &MBB, 109 const MipsInstrInfo &MipsII) { 110 bool Modified = false; 111 112 MachineBasicBlock::instr_iterator NextMII; 113 114 // Iterate through the instructions in the basic block 115 for (MachineBasicBlock::instr_iterator MII = MBB.instr_begin(), 116 E = MBB.instr_end(); 117 MII != E; MII = NextMII) { 118 119 NextMII = next_nodbg(MII, E); 120 121 // Trigger when the current instruction is a mul and the next instruction 122 // is either a mul or a branch in case the branch target start with a mul 123 if (NextMII != E && isFirstMul(*MII) && isSecondMulOrBranch(*NextMII)) { 124 LLVM_DEBUG(dbgs() << "Found mulmul!\n"); 125 126 const MCInstrDesc &NewMCID = MipsII.get(Mips::NOP); 127 BuildMI(MBB, NextMII, DebugLoc(), NewMCID); 128 Modified = true; 129 } 130 } 131 132 return Modified; 133 } 134 135 FunctionPass *llvm::createMipsMulMulBugPass() { return new MipsMulMulBugFix(); } 136