Do not track subregister liveness when it brings no benefits

Some subregisters are only to indicate different access sizes, while not
providing any way to actually divide the register up into multiple
disjunct parts. Avoid tracking subregister liveness in these cases as it
is not beneficial.

Differential Revision: http://reviews.llvm.org/D8429

llvm-svn: 232695

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/LiveRangeCalc.cpp b/llvm/lib/CodeGen/LiveRangeCalc.cpp
index d804b39c597..45e7265c8f4 100644
--- a/llvm/lib/CodeGen/LiveRangeCalc.cpp
+++ b/llvm/lib/CodeGen/LiveRangeCalc.cpp
@@ -50,7 +50,7 @@ static void createDeadDef(SlotIndexes &Indexes, VNInfo::Allocator &Alloc,
     LR.createDeadDef(DefIdx, Alloc);
 }
 
-void LiveRangeCalc::calculate(LiveInterval &LI) {
+void LiveRangeCalc::calculate(LiveInterval &LI, bool TrackSubRegs) {
   assert(MRI && Indexes && "call reset() first");
 
   // Step 1: Create minimal live segments for every definition of Reg.
@@ -63,7 +63,7 @@ void LiveRangeCalc::calculate(LiveInterval &LI) {
       continue;
 
     unsigned SubReg = MO.getSubReg();
-    if (LI.hasSubRanges() || (SubReg != 0 && MRI->tracksSubRegLiveness())) {
+    if (LI.hasSubRanges() || (SubReg != 0 && TrackSubRegs)) {
       unsigned Mask = SubReg != 0 ? TRI.getSubRegIndexLaneMask(SubReg)
                                   : MRI->getMaxLaneMaskForVReg(Reg);