+} // end anonymous namespace
+
+static unsigned getRelaxedOpcodeBranch(unsigned Op) {
+ switch (Op) {
+ default:
+ return Op;
+
+ case X86::JAE_1: return X86::JAE_4;
+ case X86::JA_1: return X86::JA_4;
+ case X86::JBE_1: return X86::JBE_4;
+ case X86::JB_1: return X86::JB_4;
+ case X86::JE_1: return X86::JE_4;
+ case X86::JGE_1: return X86::JGE_4;
+ case X86::JG_1: return X86::JG_4;
+ case X86::JLE_1: return X86::JLE_4;
+ case X86::JL_1: return X86::JL_4;
+ case X86::JMP_1: return X86::JMP_4;
+ case X86::JNE_1: return X86::JNE_4;
+ case X86::JNO_1: return X86::JNO_4;
+ case X86::JNP_1: return X86::JNP_4;
+ case X86::JNS_1: return X86::JNS_4;
+ case X86::JO_1: return X86::JO_4;
+ case X86::JP_1: return X86::JP_4;
+ case X86::JS_1: return X86::JS_4;
+ }
+}
+
+static unsigned getRelaxedOpcodeArith(unsigned Op) {
+ switch (Op) {
+ default:
+ return Op;
+
+ // IMUL
+ case X86::IMUL16rri8: return X86::IMUL16rri;
+ case X86::IMUL16rmi8: return X86::IMUL16rmi;
+ case X86::IMUL32rri8: return X86::IMUL32rri;
+ case X86::IMUL32rmi8: return X86::IMUL32rmi;
+ case X86::IMUL64rri8: return X86::IMUL64rri32;
+ case X86::IMUL64rmi8: return X86::IMUL64rmi32;
+
+ // AND
+ case X86::AND16ri8: return X86::AND16ri;
+ case X86::AND16mi8: return X86::AND16mi;
+ case X86::AND32ri8: return X86::AND32ri;
+ case X86::AND32mi8: return X86::AND32mi;
+ case X86::AND64ri8: return X86::AND64ri32;
+ case X86::AND64mi8: return X86::AND64mi32;
+
+ // OR
+ case X86::OR16ri8: return X86::OR16ri;
+ case X86::OR16mi8: return X86::OR16mi;
+ case X86::OR32ri8: return X86::OR32ri;
+ case X86::OR32mi8: return X86::OR32mi;
+ case X86::OR64ri8: return X86::OR64ri32;
+ case X86::OR64mi8: return X86::OR64mi32;
+
+ // XOR
+ case X86::XOR16ri8: return X86::XOR16ri;
+ case X86::XOR16mi8: return X86::XOR16mi;
+ case X86::XOR32ri8: return X86::XOR32ri;
+ case X86::XOR32mi8: return X86::XOR32mi;
+ case X86::XOR64ri8: return X86::XOR64ri32;
+ case X86::XOR64mi8: return X86::XOR64mi32;
+
+ // ADD
+ case X86::ADD16ri8: return X86::ADD16ri;
+ case X86::ADD16mi8: return X86::ADD16mi;
+ case X86::ADD32ri8: return X86::ADD32ri;
+ case X86::ADD32mi8: return X86::ADD32mi;
+ case X86::ADD64ri8: return X86::ADD64ri32;
+ case X86::ADD64mi8: return X86::ADD64mi32;
+
+ // SUB
+ case X86::SUB16ri8: return X86::SUB16ri;
+ case X86::SUB16mi8: return X86::SUB16mi;
+ case X86::SUB32ri8: return X86::SUB32ri;
+ case X86::SUB32mi8: return X86::SUB32mi;
+ case X86::SUB64ri8: return X86::SUB64ri32;
+ case X86::SUB64mi8: return X86::SUB64mi32;
+
+ // CMP
+ case X86::CMP16ri8: return X86::CMP16ri;
+ case X86::CMP16mi8: return X86::CMP16mi;
+ case X86::CMP32ri8: return X86::CMP32ri;
+ case X86::CMP32mi8: return X86::CMP32mi;
+ case X86::CMP64ri8: return X86::CMP64ri32;
+ case X86::CMP64mi8: return X86::CMP64mi32;
+ }
+}
+
+static unsigned getRelaxedOpcode(unsigned Op) {
+ unsigned R = getRelaxedOpcodeArith(Op);
+ if (R != Op)
+ return R;
+ return getRelaxedOpcodeBranch(Op);
+}
+
+bool X86AsmBackend::MayNeedRelaxation(const MCInst &Inst) const {
+ // Branches can always be relaxed.
+ if (getRelaxedOpcodeBranch(Inst.getOpcode()) != Inst.getOpcode())
+ return true;
+
+ // Check if this instruction is ever relaxable.
+ if (getRelaxedOpcodeArith(Inst.getOpcode()) == Inst.getOpcode())
+ return false;
+
+
+ // Check if it has an expression and is not RIP relative.
+ bool hasExp = false;
+ bool hasRIP = false;
+ for (unsigned i = 0; i < Inst.getNumOperands(); ++i) {
+ const MCOperand &Op = Inst.getOperand(i);
+ if (Op.isExpr())
+ hasExp = true;
+
+ if (Op.isReg() && Op.getReg() == X86::RIP)
+ hasRIP = true;
+ }
+
+ // FIXME: Why exactly do we need the !hasRIP? Is it just a limitation on
+ // how we do relaxations?
+ return hasExp && !hasRIP;
+}
+
+// FIXME: Can tblgen help at all here to verify there aren't other instructions
+// we can relax?
+void X86AsmBackend::RelaxInstruction(const MCInst &Inst, MCInst &Res) const {
+ // The only relaxations X86 does is from a 1byte pcrel to a 4byte pcrel.
+ unsigned RelaxedOp = getRelaxedOpcode(Inst.getOpcode());
+
+ if (RelaxedOp == Inst.getOpcode()) {
+ SmallString<256> Tmp;
+ raw_svector_ostream OS(Tmp);
+ Inst.dump_pretty(OS);
+ OS << "\n";
+ report_fatal_error("unexpected instruction to relax: " + OS.str());
+ }