+/// isPostDominatedBy - Return true if A is post dominated by B.
+static bool isPostDominatedBy(MachineBasicBlock *A, MachineBasicBlock *B) {
+
+ // FIXME - Use real post dominator.
+ if (A->succ_size() != 2)
+ return false;
+ MachineBasicBlock::succ_iterator I = A->succ_begin();
+ if (B == *I)
+ ++I;
+ MachineBasicBlock *OtherSuccBlock = *I;
+ if (OtherSuccBlock->succ_size() != 1 ||
+ *(OtherSuccBlock->succ_begin()) != B)
+ return false;
+
+ return true;
+}
+
+/// isProfitableToSinkTo - Return true if it is profitable to sink MI.
+bool MachineSinking::isProfitableToSinkTo(unsigned Reg, MachineInstr *MI,
+ MachineBasicBlock *MBB,
+ MachineBasicBlock *SuccToSinkTo) {
+ assert (MI && "Invalid MachineInstr!");
+ assert (SuccToSinkTo && "Invalid SinkTo Candidate BB");
+
+ if (MBB == SuccToSinkTo)
+ return false;
+
+ // It is profitable if SuccToSinkTo does not post dominate current block.
+ if (!isPostDominatedBy(MBB, SuccToSinkTo))
+ return true;
+
+ // Check if only use in post dominated block is PHI instruction.
+ bool NonPHIUse = false;
+ for (MachineRegisterInfo::use_nodbg_iterator
+ I = MRI->use_nodbg_begin(Reg), E = MRI->use_nodbg_end();
+ I != E; ++I) {
+ MachineInstr *UseInst = &*I;
+ MachineBasicBlock *UseBlock = UseInst->getParent();
+ if (UseBlock == SuccToSinkTo && !UseInst->isPHI())
+ NonPHIUse = true;
+ }
+ if (!NonPHIUse)
+ return true;
+
+ // If SuccToSinkTo post dominates then also it may be profitable if MI
+ // can further profitably sinked into another block in next round.
+ bool BreakPHIEdge = false;
+ // FIXME - If finding successor is compile time expensive then catch results.
+ if (MachineBasicBlock *MBB2 = FindSuccToSinkTo(MI, SuccToSinkTo, BreakPHIEdge))
+ return isProfitableToSinkTo(Reg, MI, SuccToSinkTo, MBB2);
+
+ // If SuccToSinkTo is final destination and it is a post dominator of current
+ // block then it is not profitable to sink MI into SuccToSinkTo block.
+ return false;
+}
+