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/CommandLine.h" 28 #include "llvm/Support/Debug.h" 29 #include "llvm/Target/TargetMachine.h" 30 31 #define DEBUG_TYPE "mips-vr4300-mulmul-fix" 32 33 using namespace llvm; 34 35 namespace { 36 37 class MipsMulMulBugFix : public MachineFunctionPass { 38 public: 39 MipsMulMulBugFix() : MachineFunctionPass(ID) { 40 initializeMipsMulMulBugFixPass(*PassRegistry::getPassRegistry()); 41 } 42 43 StringRef getPassName() const override { return "Mips VR4300 mulmul bugfix"; } 44 45 MachineFunctionProperties getRequiredProperties() const override { 46 return MachineFunctionProperties().set( 47 MachineFunctionProperties::Property::NoVRegs); 48 } 49 50 bool runOnMachineFunction(MachineFunction &MF) override; 51 52 static char ID; 53 54 private: 55 bool fixMulMulBB(MachineBasicBlock &MBB, const MipsInstrInfo &MipsII); 56 }; 57 58 } // namespace 59 60 INITIALIZE_PASS(MipsMulMulBugFix, "mips-vr4300-mulmul-fix", 61 "Mips VR4300 mulmul bugfix", false, false) 62 63 char MipsMulMulBugFix::ID = 0; 64 65 bool MipsMulMulBugFix::runOnMachineFunction(MachineFunction &MF) { 66 const MipsInstrInfo &MipsII = 67 *static_cast<const MipsInstrInfo *>(MF.getSubtarget().getInstrInfo()); 68 69 bool Modified = false; 70 71 for (auto &MBB : MF) 72 Modified |= fixMulMulBB(MBB, MipsII); 73 74 return Modified; 75 } 76 77 static bool isFirstMul(const MachineInstr &MI) { 78 switch (MI.getOpcode()) { 79 case Mips::FMUL_S: 80 case Mips::FMUL_D: 81 case Mips::FMUL_D32: 82 case Mips::FMUL_D64: 83 return true; 84 default: 85 return false; 86 } 87 } 88 89 static bool isSecondMulOrBranch(const MachineInstr &MI) { 90 if (MI.isBranch() || MI.isIndirectBranch() || MI.isCall()) 91 return true; 92 93 switch (MI.getOpcode()) { 94 case Mips::MUL: 95 case Mips::FMUL_S: 96 case Mips::FMUL_D: 97 case Mips::FMUL_D32: 98 case Mips::FMUL_D64: 99 case Mips::MULT: 100 case Mips::MULTu: 101 case Mips::DMULT: 102 case Mips::DMULTu: 103 return true; 104 default: 105 return false; 106 } 107 } 108 109 bool MipsMulMulBugFix::fixMulMulBB(MachineBasicBlock &MBB, 110 const MipsInstrInfo &MipsII) { 111 bool Modified = false; 112 113 MachineBasicBlock::instr_iterator NextMII; 114 115 // Iterate through the instructions in the basic block 116 for (MachineBasicBlock::instr_iterator MII = MBB.instr_begin(), 117 E = MBB.instr_end(); 118 MII != E; MII = NextMII) { 119 120 NextMII = next_nodbg(MII, E); 121 122 // Trigger when the current instruction is a mul and the next instruction 123 // is either a mul or a branch in case the branch target start with a mul 124 if (NextMII != E && isFirstMul(*MII) && isSecondMulOrBranch(*NextMII)) { 125 LLVM_DEBUG(dbgs() << "Found mulmul!\n"); 126 127 const MCInstrDesc &NewMCID = MipsII.get(Mips::NOP); 128 BuildMI(MBB, NextMII, DebugLoc(), NewMCID); 129 Modified = true; 130 } 131 } 132 133 return Modified; 134 } 135 136 FunctionPass *llvm::createMipsMulMulBugPass() { return new MipsMulMulBugFix(); } 137