+bool PPCFrameLowering::findScratchRegister(MachineBasicBlock *MBB,
+ bool UseAtEnd,
+ unsigned *ScratchRegister) const {
+ RegScavenger RS;
+ unsigned R0 = Subtarget.isPPC64() ? PPC::X0 : PPC::R0;
+
+ if (ScratchRegister)
+ *ScratchRegister = R0;
+
+ // If MBB is an entry or exit block, use R0 as the scratch register
+ if ((UseAtEnd && MBB->isReturnBlock()) ||
+ (!UseAtEnd && (&MBB->getParent()->front() == MBB)))
+ return true;
+
+ RS.enterBasicBlock(MBB);
+
+ if (UseAtEnd && !MBB->empty()) {
+ // The scratch register will be used at the end of the block, so must consider
+ // all registers used within the block
+
+ MachineBasicBlock::iterator MBBI = MBB->getFirstTerminator();
+ // If no terminator, back iterator up to previous instruction.
+ if (MBBI == MBB->end())
+ MBBI = std::prev(MBBI);
+
+ if (MBBI != MBB->begin())
+ RS.forward(MBBI);
+ }
+
+ if (!RS.isRegUsed(R0))
+ return true;
+
+ unsigned Reg = RS.FindUnusedReg(Subtarget.isPPC64() ? &PPC::G8RCRegClass
+ : &PPC::GPRCRegClass);
+
+ // Make sure the register scavenger was able to find an available register
+ // If not, use R0 but return false to indicate no register was available and
+ // R0 must be used (as recommended by the ABI)
+ if (Reg == 0)
+ return false;
+
+ if (ScratchRegister)
+ *ScratchRegister = Reg;
+
+ return true;
+}
+
+bool PPCFrameLowering::canUseAsPrologue(const MachineBasicBlock &MBB) const {
+ MachineBasicBlock *TmpMBB = const_cast<MachineBasicBlock *>(&MBB);
+
+ return findScratchRegister(TmpMBB, false, nullptr);
+}
+
+bool PPCFrameLowering::canUseAsEpilogue(const MachineBasicBlock &MBB) const {
+ MachineBasicBlock *TmpMBB = const_cast<MachineBasicBlock *>(&MBB);
+
+ return findScratchRegister(TmpMBB, true, nullptr);
+}
+