1 files changed, 11 insertions, 2 deletions
diff --git a/lib/CodeGen/RegAllocFast.cpp b/lib/CodeGen/RegAllocFast.cpp
index c606b7b833104..d5538be4bba25 100644
--- a/lib/CodeGen/RegAllocFast.cpp
+++ b/lib/CodeGen/RegAllocFast.cpp
@@ -203,6 +203,8 @@ namespace {
   char RAFast::ID = 0;
 }
 
+INITIALIZE_PASS(RAFast, "regallocfast", "Fast Register Allocator", false, false)
+
 /// getStackSpaceFor - This allocates space for the specified virtual register
 /// to be held on the stack.
 int RAFast::getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC) {
@@ -244,8 +246,15 @@ void RAFast::addKillFlag(const LiveReg &LR) {
   if (MO.isUse() && !LR.LastUse->isRegTiedToDefOperand(LR.LastOpNum)) {
     if (MO.getReg() == LR.PhysReg)
       MO.setIsKill();
-    else
-      LR.LastUse->addRegisterKilled(LR.PhysReg, TRI, true);
+    // else, don't do anything we are problably redefining a
+    // subreg of this register and given we don't track which
+    // lanes are actually dead, we cannot insert a kill flag here.
+    // Otherwise we may end up in a situation like this:
+    // ... = (MO) physreg:sub1, physreg <implicit-use, kill>
+    // ... <== Here we would allow later pass to reuse physreg:sub1
+    //         which is potentially wrong.
+    // LR:sub0 = ...
+    // ... = LR.sub1 <== This is going to use physreg:sub1
   }
 }