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

6 files changed, 12 insertions, 11 deletions

diff --git a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
index cc08045c7b8..adca4cc738e 100644
--- a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -199,7 +199,7 @@ void LiveIntervals::computeVirtRegInterval(LiveInterval &LI) {
   assert(LRCalc && "LRCalc not initialized.");
   assert(LI.empty() && "Should only compute empty intervals.");
   LRCalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
-  LRCalc->calculate(LI);
+  LRCalc->calculate(LI, MRI->shouldTrackSubRegLiveness(LI.reg));
   computeDeadValues(LI, nullptr);
 }
 
@@ -466,7 +466,7 @@ bool LiveIntervals::computeDeadValues(LiveInterval &LI,
 
     // Is the register live before? Otherwise we may have to add a read-undef
     // flag for subregister defs.
-    if (MRI->tracksSubRegLiveness()) {
+    if (MRI->shouldTrackSubRegLiveness(LI.reg)) {
       if ((I == LI.begin() || std::prev(I)->end < Def) && !VNI->isPHIDef()) {
         MachineInstr *MI = getInstructionFromIndex(Def);
         MI->addRegisterDefReadUndef(LI.reg);
@@ -662,7 +662,7 @@ void LiveIntervals::addKillFlags(const VirtRegMap *VRM) {
       RU.push_back(std::make_pair(&RURange, RURange.find(LI.begin()->end)));
     }
 
-    if (MRI->tracksSubRegLiveness()) {
+    if (MRI->subRegLivenessEnabled()) {
       SRs.clear();
       for (const LiveInterval::SubRange &SR : LI.subranges()) {
         SRs.push_back(std::make_pair(&SR, SR.find(LI.begin()->end)));
@@ -700,7 +700,7 @@ void LiveIntervals::addKillFlags(const VirtRegMap *VRM) {
         goto CancelKill;
       }
 
-      if (MRI->tracksSubRegLiveness()) {
+      if (MRI->subRegLivenessEnabled()) {
         // When reading a partial undefined value we must not add a kill flag.
         // The regalloc might have used the undef lane for something else.
         // Example:
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);
 
diff --git a/llvm/lib/CodeGen/LiveRangeCalc.h b/llvm/lib/CodeGen/LiveRangeCalc.h
index 90bf97172e5..34d99534834 100644
--- a/llvm/lib/CodeGen/LiveRangeCalc.h
+++ b/llvm/lib/CodeGen/LiveRangeCalc.h
@@ -187,7 +187,7 @@ public:
   /// Calculates liveness for the register specified in live interval @p LI.
   /// Creates subregister live ranges as needed if subreg liveness tracking is
   /// enabled.
-  void calculate(LiveInterval &LI);
+  void calculate(LiveInterval &LI, bool TrackSubRegs);
 
   //===--------------------------------------------------------------------===//
   // Low-level interface.
diff --git a/llvm/lib/CodeGen/MachineVerifier.cpp b/llvm/lib/CodeGen/MachineVerifier.cpp
index d39733be6c4..22990e3d5d7 100644
--- a/llvm/lib/CodeGen/MachineVerifier.cpp
+++ b/llvm/lib/CodeGen/MachineVerifier.cpp
@@ -1573,7 +1573,8 @@ void MachineVerifier::verifyLiveRangeSegment(const LiveRange &LR,
       if (!hasRead) {
         // When tracking subregister liveness, the main range must start new
         // values on partial register writes, even if there is no read.
-        if (!MRI->tracksSubRegLiveness() || LaneMask != 0 || !hasSubRegDef) {
+        if (!MRI->shouldTrackSubRegLiveness(Reg) || LaneMask != 0 ||
+            !hasSubRegDef) {
           report("Instruction ending live segment doesn't read the register",
                  MI);
           errs() << S << " in " << LR << '\n';
diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
index 0ee149f40b3..47bd4cc2fae 100644
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -1145,7 +1145,7 @@ void RegisterCoalescer::updateRegDefsUses(unsigned SrcReg,
 
       // A subreg use of a partially undef (super) register may be a complete
       // undef use now and then has to be marked that way.
-      if (SubIdx != 0 && MO.isUse() && MRI->tracksSubRegLiveness()) {
+      if (SubIdx != 0 && MO.isUse() && MRI->shouldTrackSubRegLiveness(DstReg)) {
         if (!DstInt->hasSubRanges()) {
           BumpPtrAllocator &Allocator = LIS->getVNInfoAllocator();
           unsigned Mask = MRI->getMaxLaneMaskForVReg(DstInt->reg);
@@ -2479,7 +2479,7 @@ bool RegisterCoalescer::joinVirtRegs(CoalescerPair &CP) {
   SmallVector<VNInfo*, 16> NewVNInfo;
   LiveInterval &RHS = LIS->getInterval(CP.getSrcReg());
   LiveInterval &LHS = LIS->getInterval(CP.getDstReg());
-  bool TrackSubRegLiveness = MRI->tracksSubRegLiveness();
+  bool TrackSubRegLiveness = MRI->shouldTrackSubRegLiveness(*CP.getNewRC());
   JoinVals RHSVals(RHS, CP.getSrcReg(), CP.getSrcIdx(), 0, NewVNInfo, CP, LIS,
                    TRI, false, TrackSubRegLiveness);
   JoinVals LHSVals(LHS, CP.getDstReg(), CP.getDstIdx(), 0, NewVNInfo, CP, LIS,
diff --git a/llvm/lib/CodeGen/VirtRegMap.cpp b/llvm/lib/CodeGen/VirtRegMap.cpp
index 7d3b0cea1c1..d9adfdf7b2e 100644
--- a/llvm/lib/CodeGen/VirtRegMap.cpp
+++ b/llvm/lib/CodeGen/VirtRegMap.cpp
@@ -286,7 +286,7 @@ void VirtRegRewriter::addMBBLiveIns() {
 }
 
 void VirtRegRewriter::rewrite() {
-  bool NoSubRegLiveness = !MRI->tracksSubRegLiveness();
+  bool NoSubRegLiveness = !MRI->subRegLivenessEnabled();
   SmallVector<unsigned, 8> SuperDeads;
   SmallVector<unsigned, 8> SuperDefs;
   SmallVector<unsigned, 8> SuperKills;