- const TargetRegisterClass *TRC = MRI->getRegClass(VReg);
- const TargetRegisterClass *SRC = TRC->getSubRegisterRegClass(SubIdx);
- assert(SRC && "Invalid subregister index in EXTRACT_SUBREG");
-
- // Figure out the register class to create for the destreg.
- // Note that if we're going to directly use an existing register,
- // it must be precisely the required class, and not a subclass
- // thereof.
- if (VRBase == 0 || SRC != MRI->getRegClass(VRBase)) {
- // Create the reg
- assert(SRC && "Couldn't find source register class");
- VRBase = MRI->createVirtualRegister(SRC);
+ MachineInstr *DefMI = MRI->getVRegDef(VReg);
+ unsigned SrcReg, DstReg, DefSubIdx;
+ if (DefMI &&
+ TII->isCoalescableExtInstr(*DefMI, SrcReg, DstReg, DefSubIdx) &&
+ SubIdx == DefSubIdx &&
+ TRC == MRI->getRegClass(SrcReg)) {
+ // Optimize these:
+ // r1025 = s/zext r1024, 4
+ // r1026 = extract_subreg r1025, 4
+ // to a copy
+ // r1026 = copy r1024
+ VRBase = MRI->createVirtualRegister(TRC);
+ BuildMI(*MBB, InsertPos, Node->getDebugLoc(),
+ TII->get(TargetOpcode::COPY), VRBase).addReg(SrcReg);
+ MRI->clearKillFlags(SrcReg);
+ } else {
+ // VReg may not support a SubIdx sub-register, and we may need to
+ // constrain its register class or issue a COPY to a compatible register
+ // class.
+ VReg = ConstrainForSubReg(VReg, SubIdx,
+ Node->getOperand(0).getValueType(),
+ Node->getDebugLoc());
+
+ // Create the destreg if it is missing.
+ if (VRBase == 0)
+ VRBase = MRI->createVirtualRegister(TRC);
+
+ // Create the extract_subreg machine instruction.
+ BuildMI(*MBB, InsertPos, Node->getDebugLoc(),
+ TII->get(TargetOpcode::COPY), VRBase).addReg(VReg, 0, SubIdx);