- // not in the same basic block as the given instruction.
- MachineBasicBlock *MBB = MI->getParent();
- if (CSMI->getParent() != MBB)
- return false;
+ // not in the same basic block as the given instruction. The only exception
+ // is if the common subexpression is in the sole predecessor block.
+ const MachineBasicBlock *MBB = MI->getParent();
+ const MachineBasicBlock *CSMBB = CSMI->getParent();
+
+ bool CrossMBB = false;
+ if (CSMBB != MBB) {
+ if (MBB->pred_size() != 1 || *MBB->pred_begin() != CSMBB)
+ return false;
+
+ for (unsigned i = 0, e = PhysDefs.size(); i != e; ++i) {
+ if (AllocatableRegs.test(PhysDefs[i]) || ReservedRegs.test(PhysDefs[i]))
+ // Avoid extending live range of physical registers if they are
+ //allocatable or reserved.
+ return false;
+ }
+ CrossMBB = true;
+ }