LiveRangeEdit: Fix liveranges not shrinking on subrange kill.

If a dead instruction we may not only have a last-use in the main live
range but also in a subregister range if subregisters are tracked. We
need to partially rebuild live ranges in both cases.

The testcase only broke when subregister liveness was enabled. I
commited it in the current form because there is currently no flag to
enable/disable subregister liveness.

This fixes PR23720.

llvm-svn: 238785

1 files changed, 18 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/LiveRangeEdit.cpp b/llvm/lib/CodeGen/LiveRangeEdit.cpp
index 27c57d5f302..08bbe0c3f37 100644
--- a/llvm/lib/CodeGen/LiveRangeEdit.cpp
+++ b/llvm/lib/CodeGen/LiveRangeEdit.cpp
@@ -218,6 +218,22 @@ bool LiveRangeEdit::foldAsLoad(LiveInterval *LI,
   return true;
 }
 
+bool LiveRangeEdit::useIsKill(const LiveInterval &LI,
+                              const MachineOperand &MO) const {
+  const MachineInstr *MI = MO.getParent();
+  SlotIndex Idx = LIS.getInstructionIndex(MI).getRegSlot();
+  if (LI.Query(Idx).isKill())
+    return true;
+  const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo();
+  unsigned SubReg = MO.getSubReg();
+  unsigned LaneMask = TRI.getSubRegIndexLaneMask(SubReg);
+  for (const LiveInterval::SubRange &S : LI.subranges()) {
+    if ((S.LaneMask & LaneMask) != 0 && S.Query(Idx).isKill())
+      return true;
+  }
+  return false;
+}
+
 /// Find all live intervals that need to shrink, then remove the instruction.
 void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
   assert(MI->allDefsAreDead() && "Def isn't really dead");
@@ -266,9 +282,8 @@ void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
     // unlikely to change anything. We typically don't want to shrink the
     // PIC base register that has lots of uses everywhere.
     // Always shrink COPY uses that probably come from live range splitting.
-    if (MI->readsVirtualRegister(Reg) &&
-        (MI->isCopy() || MOI->isDef() || MRI.hasOneNonDBGUse(Reg) ||
-         LI.Query(Idx).isKill()))
+    if ((MI->readsVirtualRegister(Reg) && (MI->isCopy() || MOI->isDef())) ||
+        (MOI->readsReg() && (MRI.hasOneNonDBGUse(Reg) || useIsKill(LI, *MOI))))
       ToShrink.insert(&LI);
 
     // Remove defined value.