LiveIntervalAnalysis: Avoid multiple connected liveness components

[oota-llvm.git] / lib / CodeGen / LiveIntervalAnalysis.cpp

diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 1160dcf4121ae708f651feec8e12f236c5905925..de0fa7c7da5fc36fbb895d11a32de846f6b7750f 100644 (file)
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -198,9 +198,16 @@ LiveInterval* LiveIntervals::createInterval(unsigned reg) {
 void LiveIntervals::computeVirtRegInterval(LiveInterval &LI) {
   assert(LRCalc && "LRCalc not initialized.");
   assert(LI.empty() && "Should only compute empty intervals.");
+  bool ShouldTrackSubRegLiveness = MRI->shouldTrackSubRegLiveness(LI.reg);
   LRCalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
-  LRCalc->calculate(LI, MRI->shouldTrackSubRegLiveness(LI.reg));
-  computeDeadValues(LI, nullptr);
+  LRCalc->calculate(LI, ShouldTrackSubRegLiveness);
+  bool SeparatedComponents = computeDeadValues(LI, nullptr);
+  if (SeparatedComponents) {
+    assert(ShouldTrackSubRegLiveness
+           && "Separated components should only occur for unused subreg defs");
+    SmallVector<LiveInterval*, 8> SplitLIs;
+    splitSeparateComponents(LI, SplitLIs);
+  }
 }
 
 void LiveIntervals::computeVirtRegs() {
@@ -457,7 +464,7 @@ bool LiveIntervals::shrinkToUses(LiveInterval *li,
 
 bool LiveIntervals::computeDeadValues(LiveInterval &LI,
                                       SmallVectorImpl<MachineInstr*> *dead) {
-  bool PHIRemoved = false;
+  bool MayHaveSplitComponents = false;
   for (auto VNI : LI.valnos) {
     if (VNI->isUnused())
       continue;
@@ -467,10 +474,13 @@ 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->shouldTrackSubRegLiveness(LI.reg)) {
+    bool DeadBeforeDef = false;
+    unsigned VReg = LI.reg;
+    if (MRI->shouldTrackSubRegLiveness(VReg)) {
       if ((I == LI.begin() || std::prev(I)->end < Def) && !VNI->isPHIDef()) {
         MachineInstr *MI = getInstructionFromIndex(Def);
-        MI->addRegisterDefReadUndef(LI.reg);
+        MI->addRegisterDefReadUndef(VReg);
+        DeadBeforeDef = true;
       }
     }
 
@@ -481,19 +491,27 @@ bool LiveIntervals::computeDeadValues(LiveInterval &LI,
       VNI->markUnused();
       LI.removeSegment(I);
       DEBUG(dbgs() << "Dead PHI at " << Def << " may separate interval\n");
-      PHIRemoved = true;
+      MayHaveSplitComponents = true;
     } else {
       // This is a dead def. Make sure the instruction knows.
       MachineInstr *MI = getInstructionFromIndex(Def);
       assert(MI && "No instruction defining live value");
-      MI->addRegisterDead(LI.reg, TRI);
+      MI->addRegisterDead(VReg, TRI);
+
+      // If we have a dead def that is completely separate from the rest of
+      // the liverange then we rewrite it to use a different VReg to not violate
+      // the rule that the liveness of a virtual register forms a connected
+      // component. This should only happen if subregister liveness is tracked.
+      if (DeadBeforeDef)
+        MayHaveSplitComponents = true;
+
       if (dead && MI->allDefsAreDead()) {
         DEBUG(dbgs() << "All defs dead: " << Def << '\t' << *MI);
         dead->push_back(MI);
       }
     }
   }
-  return PHIRemoved;
+  return MayHaveSplitComponents;
 }
 
 void LiveIntervals::shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg)