+bool ARMAsmBackend::fixupNeedsRelaxation(const MCFixup &Fixup,
+ uint64_t Value,
+ const MCInstFragment *DF,
+ const MCAsmLayout &Layout) const {
+ switch ((unsigned)Fixup.getKind()) {
+ case ARM::fixup_arm_thumb_br: {
+ // Relaxing tB to t2B. tB has a signed 12-bit displacement with the
+ // low bit being an implied zero. There's an implied +4 offset for the
+ // branch, so we adjust the other way here to determine what's
+ // encodable.
+ //
+ // Relax if the value is too big for a (signed) i8.
+ int64_t Offset = int64_t(Value) - 4;
+ return Offset > 2046 || Offset < -2048;
+ }
+ case ARM::fixup_arm_thumb_bcc: {
+ // Relaxing tBcc to t2Bcc. tBcc has a signed 9-bit displacement with the
+ // low bit being an implied zero. There's an implied +4 offset for the
+ // branch, so we adjust the other way here to determine what's
+ // encodable.
+ //
+ // Relax if the value is too big for a (signed) i8.
+ int64_t Offset = int64_t(Value) - 4;
+ return Offset > 254 || Offset < -256;
+ }
+ case ARM::fixup_thumb_adr_pcrel_10:
+ case ARM::fixup_arm_thumb_cp: {
+ // If the immediate is negative, greater than 1020, or not a multiple
+ // of four, the wide version of the instruction must be used.
+ int64_t Offset = int64_t(Value) - 4;
+ return Offset > 1020 || Offset < 0 || Offset & 3;
+ }
+ }
+ llvm_unreachable("Unexpected fixup kind in fixupNeedsRelaxation()!");
+}
+
+void ARMAsmBackend::relaxInstruction(const MCInst &Inst, MCInst &Res) const {
+ unsigned RelaxedOp = getRelaxedOpcode(Inst.getOpcode());
+
+ // Sanity check w/ diagnostic if we get here w/ a bogus instruction.
+ 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());
+ }
+
+ // The instructions we're relaxing have (so far) the same operands.
+ // We just need to update to the proper opcode.
+ Res = Inst;
+ Res.setOpcode(RelaxedOp);