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
33using namespace llvm;
34
35namespace {
36
37class MipsMulMulBugFix : public MachineFunctionPass {
38public:
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
54private:
55 bool fixMulMulBB(MachineBasicBlock &MBB, const MipsInstrInfo &MipsII);
56};
57
58} // namespace
59
60INITIALIZE_PASS(MipsMulMulBugFix, "mips-vr4300-mulmul-fix",
61 "Mips VR4300 mulmul bugfix", false, false)
62
63char MipsMulMulBugFix::ID = 0;
64
65bool 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
77static 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
89static 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
109bool 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(It: MII, End: 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(MI: *MII) && isSecondMulOrBranch(MI: *NextMII)) {
125 LLVM_DEBUG(dbgs() << "Found mulmul!\n");
126
127 const MCInstrDesc &NewMCID = MipsII.get(Mips::NOP);
128 BuildMI(BB&: MBB, I: NextMII, MIMD: DebugLoc(), MCID: NewMCID);
129 Modified = true;
130 }
131 }
132
133 return Modified;
134}
135
136FunctionPass *llvm::createMipsMulMulBugPass() { return new MipsMulMulBugFix(); }
137

source code of llvm/lib/Target/Mips/MipsMulMulBugPass.cpp