Fix Bug 4657: register scavenger asserts with subreg lowering
When LowerSubregsInstructionPass::LowerInsert eliminates an INSERT_SUBREG
instriction because it is an identity copy, make sure that the same registers
are alive before and after the elimination.
When the super-register is marked <undef> this requires inserting an
IMPLICIT_DEF instruction to make sure the super register is live.
Fix a related bug where a kill flag on the inserted sub-register was not transferred properly.
Finally, clear the undef flag in MachineInstr::addRegisterKilled. Undef implies dead and kill implies live, so they cant both be valid.
llvm-svn: 77989
diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index 006a10a..c29a6e3 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -1041,6 +1041,8 @@
if (MO.isKill())
// The register is already marked kill.
return true;
+ // This operand can no longer be undef since Reg is live-in.
+ MO.setIsUndef(false);
if (isPhysReg && isRegTiedToDefOperand(i))
// Two-address uses of physregs must not be marked kill.
return true;