From b382c4dc235b78b606b305f1913fafc20eca472c Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Thu, 16 Oct 2008 00:11:23 +0000
Subject: [PATCH] Fix a subtle bug in DeadMachineInstructionElim's liveness
 computation. A def of a register doesn't necessarily kill live
 super-registers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57614 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/DeadMachineInstructionElim.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/CodeGen/DeadMachineInstructionElim.cpp b/lib/CodeGen/DeadMachineInstructionElim.cpp
index 305ec0e7988..0d043f795a2 100644
--- a/lib/CodeGen/DeadMachineInstructionElim.cpp
+++ b/lib/CodeGen/DeadMachineInstructionElim.cpp
@@ -126,7 +126,10 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
           unsigned Reg = MO.getReg();
           if (Reg != 0 && TargetRegisterInfo::isPhysicalRegister(Reg)) {
             LivePhysRegs.reset(Reg);
-            for (const unsigned *AliasSet = TRI->getAliasSet(Reg);
+            // Check the subreg set, not the alias set, because a def
+            // of a super-register may still be partially live after
+            // this def.
+            for (const unsigned *AliasSet = TRI->getSubRegisters(Reg);
                  *AliasSet; ++AliasSet)
               LivePhysRegs.reset(*AliasSet);
           }