133 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// Early revisions of the VR4300 have a hardware bug where two consecutive10// multiplications can produce an incorrect result in the second multiply.11//12// This pass scans for mul instructions in each basic block and inserts13// a nop whenever the following conditions are met:14//15// - The current instruction is a single or double-precision floating-point16// 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 32using namespace llvm;33 34namespace {35 36class MipsMulMulBugFix : public MachineFunctionPass {37public:38 MipsMulMulBugFix() : MachineFunctionPass(ID) {}39 40 StringRef getPassName() const override { return "Mips VR4300 mulmul bugfix"; }41 42 MachineFunctionProperties getRequiredProperties() const override {43 return MachineFunctionProperties().setNoVRegs();44 }45 46 bool runOnMachineFunction(MachineFunction &MF) override;47 48 static char ID;49 50private:51 bool fixMulMulBB(MachineBasicBlock &MBB, const MipsInstrInfo &MipsII);52};53 54} // namespace55 56INITIALIZE_PASS(MipsMulMulBugFix, "mips-vr4300-mulmul-fix",57 "Mips VR4300 mulmul bugfix", false, false)58 59char MipsMulMulBugFix::ID = 0;60 61bool MipsMulMulBugFix::runOnMachineFunction(MachineFunction &MF) {62 const MipsInstrInfo &MipsII =63 *static_cast<const MipsInstrInfo *>(MF.getSubtarget().getInstrInfo());64 65 bool Modified = false;66 67 for (auto &MBB : MF)68 Modified |= fixMulMulBB(MBB, MipsII);69 70 return Modified;71}72 73static bool isFirstMul(const MachineInstr &MI) {74 switch (MI.getOpcode()) {75 case Mips::FMUL_S:76 case Mips::FMUL_D:77 case Mips::FMUL_D32:78 case Mips::FMUL_D64:79 return true;80 default:81 return false;82 }83}84 85static bool isSecondMulOrBranch(const MachineInstr &MI) {86 if (MI.isBranch() || MI.isIndirectBranch() || MI.isCall())87 return true;88 89 switch (MI.getOpcode()) {90 case Mips::MUL:91 case Mips::FMUL_S:92 case Mips::FMUL_D:93 case Mips::FMUL_D32:94 case Mips::FMUL_D64:95 case Mips::MULT:96 case Mips::MULTu:97 case Mips::DMULT:98 case Mips::DMULTu:99 return true;100 default:101 return false;102 }103}104 105bool MipsMulMulBugFix::fixMulMulBB(MachineBasicBlock &MBB,106 const MipsInstrInfo &MipsII) {107 bool Modified = false;108 109 MachineBasicBlock::instr_iterator NextMII;110 111 // Iterate through the instructions in the basic block112 for (MachineBasicBlock::instr_iterator MII = MBB.instr_begin(),113 E = MBB.instr_end();114 MII != E; MII = NextMII) {115 116 NextMII = next_nodbg(MII, E);117 118 // Trigger when the current instruction is a mul and the next instruction119 // is either a mul or a branch in case the branch target start with a mul120 if (NextMII != E && isFirstMul(*MII) && isSecondMulOrBranch(*NextMII)) {121 LLVM_DEBUG(dbgs() << "Found mulmul!\n");122 123 const MCInstrDesc &NewMCID = MipsII.get(Mips::NOP);124 BuildMI(MBB, NextMII, DebugLoc(), NewMCID);125 Modified = true;126 }127 }128 129 return Modified;130}131 132FunctionPass *llvm::createMipsMulMulBugPass() { return new MipsMulMulBugFix(); }133