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//===- MipsAnalyzeImmediate.cpp - Analyze Immediates ----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "MipsAnalyzeImmediate.h"
#include "Mips.h"
#include "llvm/Support/MathExtras.h"
#include <cassert>
#include <cstdint>
#include <iterator>
using namespace llvm;
MipsAnalyzeImmediate::Inst::Inst(unsigned O, unsigned I) : Opc(O), ImmOpnd(I) {}
// Add I to the instruction sequences.
void MipsAnalyzeImmediate::AddInstr(InstSeqLs &SeqLs, const Inst &I) {
// Add an instruction seqeunce consisting of just I.
if (SeqLs.empty()) {
SeqLs.push_back(InstSeq(1, I));
return;
}
for (auto &S : SeqLs)
S.push_back(I);
}
void MipsAnalyzeImmediate::GetInstSeqLsADDiu(uint64_t Imm, unsigned RemSize,
InstSeqLs &SeqLs) {
GetInstSeqLs((Imm + 0x8000ULL) & 0xffffffffffff0000ULL, RemSize, SeqLs);
AddInstr(SeqLs, Inst(ADDiu, Imm & 0xffffULL));
}
void MipsAnalyzeImmediate::GetInstSeqLsORi(uint64_t Imm, unsigned RemSize,
InstSeqLs &SeqLs) {
GetInstSeqLs(Imm & 0xffffffffffff0000ULL, RemSize, SeqLs);
AddInstr(SeqLs, Inst(ORi, Imm & 0xffffULL));
}
void MipsAnalyzeImmediate::GetInstSeqLsSLL(uint64_t Imm, unsigned RemSize,
InstSeqLs &SeqLs) {
unsigned Shamt = llvm::countr_zero(Imm);
GetInstSeqLs(Imm >> Shamt, RemSize - Shamt, SeqLs);
AddInstr(SeqLs, Inst(SLL, Shamt));
}
void MipsAnalyzeImmediate::GetInstSeqLs(uint64_t Imm, unsigned RemSize,
InstSeqLs &SeqLs) {
uint64_t MaskedImm = Imm & (0xffffffffffffffffULL >> (64 - Size));
// Do nothing if Imm is 0.
if (!MaskedImm)
return;
// A single ADDiu will do if RemSize <= 16.
if (RemSize <= 16) {
AddInstr(SeqLs, Inst(ADDiu, MaskedImm));
return;
}
// Shift if the lower 16-bit is cleared.
if (!(Imm & 0xffff)) {
GetInstSeqLsSLL(Imm, RemSize, SeqLs);
return;
}
GetInstSeqLsADDiu(Imm, RemSize, SeqLs);
// If bit 15 is cleared, it doesn't make a difference whether the last
// instruction is an ADDiu or ORi. In that case, do not call GetInstSeqLsORi.
if (Imm & 0x8000) {
InstSeqLs SeqLsORi;
GetInstSeqLsORi(Imm, RemSize, SeqLsORi);
SeqLs.append(std::make_move_iterator(SeqLsORi.begin()),
std::make_move_iterator(SeqLsORi.end()));
}
}
// Replace a ADDiu & SLL pair with a LUi.
// e.g. the following two instructions
// ADDiu 0x0111
// SLL 18
// are replaced with
// LUi 0x444
void MipsAnalyzeImmediate::ReplaceADDiuSLLWithLUi(InstSeq &Seq) {
// Check if the first two instructions are ADDiu and SLL and the shift amount
// is at least 16.
if ((Seq.size() < 2) || (Seq[0].Opc != ADDiu) ||
(Seq[1].Opc != SLL) || (Seq[1].ImmOpnd < 16))
return;
// Sign-extend and shift operand of ADDiu and see if it still fits in 16-bit.
int64_t Imm = SignExtend64<16>(Seq[0].ImmOpnd);
int64_t ShiftedImm = (uint64_t)Imm << (Seq[1].ImmOpnd - 16);
if (!isInt<16>(ShiftedImm))
return;
// Replace the first instruction and erase the second.
Seq[0].Opc = LUi;
Seq[0].ImmOpnd = (unsigned)(ShiftedImm & 0xffff);
Seq.erase(Seq.begin() + 1);
}
void MipsAnalyzeImmediate::GetShortestSeq(InstSeqLs &SeqLs, InstSeq &Insts) {
InstSeqLs::iterator ShortestSeq = SeqLs.end();
// The length of an instruction sequence is at most 7.
unsigned ShortestLength = 8;
for (InstSeqLs::iterator S = SeqLs.begin(); S != SeqLs.end(); ++S) {
ReplaceADDiuSLLWithLUi(*S);
assert(S->size() <= 7);
if (S->size() < ShortestLength) {
ShortestSeq = S;
ShortestLength = S->size();
}
}
Insts.clear();
Insts.append(ShortestSeq->begin(), ShortestSeq->end());
}
const MipsAnalyzeImmediate::InstSeq
&MipsAnalyzeImmediate::Analyze(uint64_t Imm, unsigned Size,
bool LastInstrIsADDiu) {
this->Size = Size;
if (Size == 32) {
ADDiu = Mips::ADDiu;
ORi = Mips::ORi;
SLL = Mips::SLL;
LUi = Mips::LUi;
} else {
ADDiu = Mips::DADDiu;
ORi = Mips::ORi64;
SLL = Mips::DSLL;
LUi = Mips::LUi64;
}
InstSeqLs SeqLs;
// Get the list of instruction sequences.
if (LastInstrIsADDiu | !Imm)
GetInstSeqLsADDiu(Imm, Size, SeqLs);
else
GetInstSeqLs(Imm, Size, SeqLs);
// Set Insts to the shortest instruction sequence.
GetShortestSeq(SeqLs, Insts);
return Insts;
}
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