+ // Check if any of the successors of TailBB has a PHI node in which the
+ // value corresponding to TailBB uses a subregister.
+ // If a phi node uses a register paired with a subregister, the actual
+ // "value type" of the phi may differ from the type of the register without
+ // any subregisters. Due to a bug, tail duplication may add a new operand
+ // without a necessary subregister, producing an invalid code. This is
+ // demonstrated by test/CodeGen/Hexagon/tail-dup-subreg-abort.ll.
+ // Disable tail duplication for this case for now, until the problem is
+ // fixed.
+ for (auto SB : TailBB.successors()) {
+ for (auto &I : *SB) {
+ if (!I.isPHI())
+ break;
+ unsigned Idx = getPHISrcRegOpIdx(&I, &TailBB);
+ assert(Idx != 0);
+ MachineOperand &PU = I.getOperand(Idx);
+ if (PU.getSubReg() != 0)
+ return false;
+ }
+ }
+