+ // Prevent use of AH in a REX instruction by referencing AX instead.
+ // Shift it down 8 bits.
+ if (HiReg == X86::AH && Subtarget->is64Bit() &&
+ !SDValue(Node, 1).use_empty()) {
+ SDValue Result = CurDAG->getCopyFromReg(CurDAG->getEntryNode(), dl,
+ X86::AX, MVT::i16, InFlag);
+ InFlag = Result.getValue(2);
+
+ // If we also need AL (the quotient), get it by extracting a subreg from
+ // Result. The fast register allocator does not like multiple CopyFromReg
+ // nodes using aliasing registers.
+ if (!SDValue(Node, 0).use_empty())
+ ReplaceUses(SDValue(Node, 0),
+ CurDAG->getTargetExtractSubreg(X86::sub_8bit, dl, MVT::i8, Result));
+
+ // Shift AX right by 8 bits instead of using AH.
+ Result = SDValue(CurDAG->getMachineNode(X86::SHR16ri, dl, MVT::i16,
+ Result,
+ CurDAG->getTargetConstant(8, MVT::i8)),
+ 0);
+ ReplaceUses(SDValue(Node, 1),
+ CurDAG->getTargetExtractSubreg(X86::sub_8bit, dl, MVT::i8, Result));
+ }