+static bool isSimpleIndexCalc(MachineInstr &I, unsigned EntryReg,
+ unsigned BaseReg) {
+ if (I.getOpcode() != ARM::t2ADDrs)
+ return false;
+
+ if (I.getOperand(0).getReg() != EntryReg)
+ return false;
+
+ if (I.getOperand(1).getReg() != BaseReg)
+ return false;
+
+ // FIXME: what about CC and IdxReg?
+ return true;
+}
+
+/// \brief While trying to form a TBB/TBH instruction, we may (if the table
+/// doesn't immediately follow the BR_JT) need access to the start of the
+/// jump-table. We know one instruction that produces such a register; this
+/// function works out whether that definition can be preserved to the BR_JT,
+/// possibly by removing an intervening addition (which is usually needed to
+/// calculate the actual entry to jump to).
+bool ARMConstantIslands::preserveBaseRegister(MachineInstr *JumpMI,
+ MachineInstr *LEAMI,
+ unsigned &DeadSize,
+ bool &CanDeleteLEA,
+ bool &BaseRegKill) {
+ if (JumpMI->getParent() != LEAMI->getParent())
+ return false;
+
+ // Now we hope that we have at least these instructions in the basic block:
+ // BaseReg = t2LEA ...
+ // [...]
+ // EntryReg = t2ADDrs BaseReg, ...
+ // [...]
+ // t2BR_JT EntryReg
+ //
+ // We have to be very conservative about what we recognise here though. The
+ // main perturbing factors to watch out for are:
+ // + Spills at any point in the chain: not direct problems but we would
+ // expect a blocking Def of the spilled register so in practice what we
+ // can do is limited.
+ // + EntryReg == BaseReg: this is the one situation we should allow a Def
+ // of BaseReg, but only if the t2ADDrs can be removed.
+ // + Some instruction other than t2ADDrs computing the entry. Not seen in
+ // the wild, but we should be careful.
+ unsigned EntryReg = JumpMI->getOperand(0).getReg();
+ unsigned BaseReg = LEAMI->getOperand(0).getReg();
+
+ CanDeleteLEA = true;
+ BaseRegKill = false;
+ MachineInstr *RemovableAdd = nullptr;
+ MachineBasicBlock::iterator I(LEAMI);
+ for (++I; &*I != JumpMI; ++I) {
+ if (isSimpleIndexCalc(*I, EntryReg, BaseReg)) {
+ RemovableAdd = &*I;
+ break;
+ }
+
+ for (unsigned K = 0, E = I->getNumOperands(); K != E; ++K) {
+ const MachineOperand &MO = I->getOperand(K);
+ if (!MO.isReg() || !MO.getReg())
+ continue;
+ if (MO.isDef() && MO.getReg() == BaseReg)
+ return false;
+ if (MO.isUse() && MO.getReg() == BaseReg) {
+ BaseRegKill = BaseRegKill || MO.isKill();
+ CanDeleteLEA = false;
+ }
+ }
+ }
+
+ if (!RemovableAdd)
+ return true;
+
+ // Check the add really is removable, and that nothing else in the block
+ // clobbers BaseReg.
+ for (++I; &*I != JumpMI; ++I) {
+ for (unsigned K = 0, E = I->getNumOperands(); K != E; ++K) {
+ const MachineOperand &MO = I->getOperand(K);
+ if (!MO.isReg() || !MO.getReg())
+ continue;
+ if (MO.isDef() && MO.getReg() == BaseReg)
+ return false;
+ if (MO.isUse() && MO.getReg() == EntryReg)
+ RemovableAdd = nullptr;
+ }
+ }
+
+ if (RemovableAdd) {
+ RemovableAdd->eraseFromParent();
+ DeadSize += 4;
+ } else if (BaseReg == EntryReg) {
+ // The add wasn't removable, but clobbered the base for the TBB. So we can't
+ // preserve it.
+ return false;
+ }
+
+ // We reached the end of the block without seeing another definition of
+ // BaseReg (except, possibly the t2ADDrs, which was removed). BaseReg can be
+ // used in the TBB/TBH if necessary.
+ return true;
+}
+
+/// \brief Returns whether CPEMI is the first instruction in the block
+/// immediately following JTMI (assumed to be a TBB or TBH terminator). If so,
+/// we can switch the first register to PC and usually remove the address
+/// calculation that preceded it.
+static bool jumpTableFollowsTB(MachineInstr *JTMI, MachineInstr *CPEMI) {
+ MachineFunction::iterator MBB = JTMI->getParent()->getIterator();
+ MachineFunction *MF = MBB->getParent();
+ ++MBB;
+
+ return MBB != MF->end() && MBB->begin() != MBB->end() &&
+ &*MBB->begin() == CPEMI;
+}
+
+/// optimizeThumb2JumpTables - Use tbb / tbh instructions to generate smaller