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 dc6b3420ab1425170c7af5aff7a5f1d3f4d29c17..8002ff2c64e08aecc295a3a2b268ae324d387125 100644 (file)
--- a/lib/CodeGen/TwoAddressInstructionPass.cpp
+++ b/lib/CodeGen/TwoAddressInstructionPass.cpp
@@ -1728,8 +1728,10 @@ TwoAddressInstructionPass::CoalesceExtSubRegs(SmallVector<unsigned,4> &Srcs,
         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 @@ TwoAddressInstructionPass::CoalesceExtSubRegs(SmallVector<unsigned,4> &Srcs,
     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.