Create subranges for new intervals resulting from live interval splitting

The register allocator can split a live interval of a register into a set
of smaller intervals. After the allocation of registers is complete, the
rewriter will modify the IR to replace virtual registers with the corres-
ponding physical registers. At this stage, if a register corresponding
to a subregister of a virtual register is used, the rewriter will check
if that subregister is undefined, and if so, it will add the <undef> flag
to the machine operand. The function verifying liveness of the subregis-
ter would assume that it is undefined, unless any of the subranges of the
live interval proves otherwise.
The problem is that the live intervals created during splitting do not
have any subranges, even if the original parent interval did. This could
result in the <undef> flag placed on a register that is actually defined.

Differential Revision: http://reviews.llvm.org/D21189

llvm-svn: 279625

1 files changed, 16 insertions, 10 deletions

diff --git a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
index 26b5cba3294..574684b19f2 100644
--- a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -504,8 +504,7 @@ bool LiveIntervals::computeDeadValues(LiveInterval &LI,
   return MayHaveSplitComponents;
 }
 
-void LiveIntervals::shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg)
-{
+void LiveIntervals::shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg) {
   DEBUG(dbgs() << "Shrink: " << SR << '\n');
   assert(TargetRegisterInfo::isVirtualRegister(Reg)
          && "Can only shrink virtual registers");
@@ -516,12 +515,14 @@ void LiveIntervals::shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg)
   SlotIndex LastIdx;
   for (MachineOperand &MO : MRI->reg_operands(Reg)) {
     MachineInstr *UseMI = MO.getParent();
-    if (UseMI->isDebugValue())
+    if (UseMI->isDebugValue() || !MO.readsReg())
       continue;
     // Maybe the operand is for a subregister we don't care about.
     unsigned SubReg = MO.getSubReg();
     if (SubReg != 0) {
       LaneBitmask LaneMask = TRI->getSubRegIndexLaneMask(SubReg);
+      if (MO.isDef())
+        LaneMask = ~LaneMask & MRI->getMaxLaneMaskForVReg(Reg);
       if ((LaneMask & SR.LaneMask) == 0)
         continue;
     }
@@ -578,7 +579,7 @@ void LiveIntervals::extendToIndices(LiveRange &LR,
   assert(LRCalc && "LRCalc not initialized.");
   LRCalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
   for (unsigned i = 0, e = Indices.size(); i != e; ++i)
-    LRCalc->extend(LR, Indices[i]);
+    LRCalc->extend(LR, Indices[i], /*PhysReg=*/0, /*Undefs=*/{});
 }
 
 void LiveIntervals::pruneValue(LiveRange &LR, SlotIndex Kill,
@@ -954,7 +955,8 @@ public:
         LiveInterval &LI = LIS.getInterval(Reg);
         if (LI.hasSubRanges()) {
           unsigned SubReg = MO.getSubReg();
-          LaneBitmask LaneMask = TRI.getSubRegIndexLaneMask(SubReg);
+          LaneBitmask LaneMask = SubReg ? TRI.getSubRegIndexLaneMask(SubReg)
+                                        : MRI.getMaxLaneMaskForVReg(Reg);
           for (LiveInterval::SubRange &S : LI.subranges()) {
             if ((S.LaneMask & LaneMask) == 0)
               continue;
@@ -1545,15 +1547,19 @@ void LiveIntervals::removePhysRegDefAt(unsigned Reg, SlotIndex Pos) {
 }
 
 void LiveIntervals::removeVRegDefAt(LiveInterval &LI, SlotIndex Pos) {
+  // LI may not have the main range computed yet, but its subranges may
+  // be present.
   VNInfo *VNI = LI.getVNInfoAt(Pos);
-  if (VNI == nullptr)
-    return;
-  LI.removeValNo(VNI);
+  if (VNI != nullptr) {
+    assert(VNI->def.getBaseIndex() == Pos.getBaseIndex());
+    LI.removeValNo(VNI);
+  }
 
-  // Also remove the value in subranges.
+  // Also remove the value defined in subranges.
   for (LiveInterval::SubRange &S : LI.subranges()) {
     if (VNInfo *SVNI = S.getVNInfoAt(Pos))
-      S.removeValNo(SVNI);
+      if (SVNI->def.getBaseIndex() == Pos.getBaseIndex())
+        S.removeValNo(SVNI);
   }
   LI.removeEmptySubRanges();
 }