-/// FindUnusedRegisters - Gather a list of allocatable registers that
-/// have not been allocated to any virtual register.
-bool VirtRegMap::FindUnusedRegisters(const TargetRegisterInfo *TRI,
- LiveIntervals* LIs) {
- unsigned NumRegs = TRI->getNumRegs();
- UnusedRegs.reset();
- UnusedRegs.resize(NumRegs);
-
- BitVector Used(NumRegs);
- for (unsigned i = TargetRegisterInfo::FirstVirtualRegister,
- e = MF->getRegInfo().getLastVirtReg(); i <= e; ++i)
- if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG)
- Used.set(Virt2PhysMap[i]);
-
- BitVector Allocatable = TRI->getAllocatableSet(*MF);
- bool AnyUnused = false;
- for (unsigned Reg = 1; Reg < NumRegs; ++Reg) {
- if (Allocatable[Reg] && !Used[Reg] && !LIs->hasInterval(Reg)) {
- bool ReallyUnused = true;
- for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
- if (Used[*AS] || LIs->hasInterval(*AS)) {
- ReallyUnused = false;
+void VirtRegRewriter::rewrite() {
+ SmallVector<unsigned, 8> SuperDeads;
+ SmallVector<unsigned, 8> SuperDefs;
+ SmallVector<unsigned, 8> SuperKills;
+ SmallPtrSet<const MachineInstr *, 4> NoReturnInsts;
+
+ // Here we have a SparseSet to hold which PhysRegs are actually encountered
+ // in the MF we are about to iterate over so that later when we call
+ // setPhysRegUsed, we are only doing it for physRegs that were actually found
+ // in the program and not for all of the possible physRegs for the given
+ // target architecture. If the target has a lot of physRegs, then for a small
+ // program there will be a significant compile time reduction here.
+ PhysRegs.clear();
+ PhysRegs.setUniverse(TRI->getNumRegs());
+
+ // The function with uwtable should guarantee that the stack unwinder
+ // can unwind the stack to the previous frame. Thus, we can't apply the
+ // noreturn optimization if the caller function has uwtable attribute.
+ bool HasUWTable = MF->getFunction()->hasFnAttribute(Attribute::UWTable);
+
+ for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
+ MBBI != MBBE; ++MBBI) {
+ DEBUG(MBBI->print(dbgs(), Indexes));
+ bool IsExitBB = MBBI->succ_empty();
+ for (MachineBasicBlock::instr_iterator
+ MII = MBBI->instr_begin(), MIE = MBBI->instr_end(); MII != MIE;) {
+ MachineInstr *MI = MII;
+ ++MII;
+
+ // Check if this instruction is a call to a noreturn function. If this
+ // is a call to noreturn function and we don't need the stack unwinding
+ // functionality (i.e. this function does not have uwtable attribute and
+ // the callee function has the nounwind attribute), then we can ignore
+ // the definitions set by this instruction.
+ if (!HasUWTable && IsExitBB && MI->isCall()) {
+ for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
+ MOE = MI->operands_end(); MOI != MOE; ++MOI) {
+ MachineOperand &MO = *MOI;
+ if (!MO.isGlobal())
+ continue;
+ const Function *Func = dyn_cast<Function>(MO.getGlobal());
+ if (!Func || !Func->hasFnAttribute(Attribute::NoReturn) ||
+ // We need to keep correct unwind information
+ // even if the function will not return, since the
+ // runtime may need it.
+ !Func->hasFnAttribute(Attribute::NoUnwind))
+ continue;
+ NoReturnInsts.insert(MI);