Preserve <def,undef> flags in CoalesceExtSubRegs.
This won't have an effect until EliminateRegSequences() starts setting
the undef flags.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148779 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/TwoAddressInstructionPass.cpp b/lib/CodeGen/TwoAddressInstructionPass.cpp
index dc6b342..8002ff2 100644
--- a/lib/CodeGen/TwoAddressInstructionPass.cpp
+++ b/lib/CodeGen/TwoAddressInstructionPass.cpp
@@ -1728,8 +1728,10 @@
CanCoalesce = false;
break;
}
- // Keep track of one of the uses.
- SomeMI = UseMI;
+ // Keep track of one of the uses. Preferably the first one which has a
+ // <def,undef> flag.
+ if (!SomeMI || UseMI->getOperand(0).isUndef())
+ SomeMI = UseMI;
}
if (!CanCoalesce)
continue;
@@ -1738,7 +1740,9 @@
MachineInstr *CopyMI = BuildMI(*SomeMI->getParent(), SomeMI,
SomeMI->getDebugLoc(),
TII->get(TargetOpcode::COPY))
- .addReg(DstReg, RegState::Define, NewDstSubIdx)
+ .addReg(DstReg, RegState::Define |
+ getUndefRegState(SomeMI->getOperand(0).isUndef()),
+ NewDstSubIdx)
.addReg(SrcReg, 0, NewSrcSubIdx);
// Remove all the old extract instructions.