Handle non-~0 lane masks on live-in registers in LivePhysRegs

When LivePhysRegs adds live-in registers, it recognizes ~0 as a special
lane mask indicating the entire register. If the lane mask is not ~0,
it will only add the subregisters that overlap the specified lane mask.

The problem is that if a live-in register does not have subregisters,
and the lane mask is not ~0, it will not be added to the live set.
(The given lane mask may simply be the lane mask of its register class.)

If a register does not have subregisters, add it to the live set if
the lane mask is non-zero.

Differential Revision: https://reviews.llvm.org/D26094

llvm-svn: 285440

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/LivePhysRegs.cpp b/llvm/lib/CodeGen/LivePhysRegs.cpp
index 7d0bf743f31..9b5d7843463 100644
--- a/llvm/lib/CodeGen/LivePhysRegs.cpp
+++ b/llvm/lib/CodeGen/LivePhysRegs.cpp
@@ -143,11 +143,12 @@ bool LivePhysRegs::available(const MachineRegisterInfo &MRI,
 /// Add live-in registers of basic block \p MBB to \p LiveRegs.
 void LivePhysRegs::addBlockLiveIns(const MachineBasicBlock &MBB) {
   for (const auto &LI : MBB.liveins()) {
-    if (LI.LaneMask == ~0u) {
+    MCSubRegIndexIterator S(LI.PhysReg, TRI);
+    if (LI.LaneMask == ~0u || (LI.LaneMask != 0 && !S.isValid())) {
       addReg(LI.PhysReg);
       continue;
     }
-    for (MCSubRegIndexIterator S(LI.PhysReg, TRI); S.isValid(); ++S)
+    for (; S.isValid(); ++S)
       if (LI.LaneMask & TRI->getSubRegIndexLaneMask(S.getSubRegIndex()))
         addReg(S.getSubReg());
   }