LiveIntervalAnalysis: Mark subregister defs as undef when we determined they are...

This was not necessary before as this case can only be detected when the
liveness analysis is at subregister level.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226733 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/MachineInstr.h b/include/llvm/CodeGen/MachineInstr.h
index bcf1f5caaa8c6c3c5c3c8850dd3791ca5059c0ac..945ee0f5d734e004c06a549ca620afff22c04ca8 100644 (file)
--- a/include/llvm/CodeGen/MachineInstr.h
+++ b/include/llvm/CodeGen/MachineInstr.h
@@ -1048,6 +1048,11 @@ public:
   bool addRegisterDead(unsigned Reg, const TargetRegisterInfo *RegInfo,
                        bool AddIfNotFound = false);
 
+  /// Mark all subregister defs of register @p Reg with the undef flag.
+  /// This function is used when we determined to have a subregister def in an
+  /// otherwise undefined super register.
+  void addRegisterDefReadUndef(unsigned Reg);
+
   /// addRegisterDefined - We have determined MI defines a register. Make sure
   /// there is an operand defining Reg.
   void addRegisterDefined(unsigned Reg,

diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index c03773f80370bb8f6261c98926bba48764764ca7..16b30ff2c2958ff52a7a43074bd49ad2125b6234 100644 (file)
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -448,23 +448,34 @@ bool LiveIntervals::computeDeadValues(LiveInterval &LI,
   for (auto VNI : LI.valnos) {
     if (VNI->isUnused())
       continue;
-    LiveRange::iterator I = LI.FindSegmentContaining(VNI->def);
+    SlotIndex Def = VNI->def;
+    LiveRange::iterator I = LI.FindSegmentContaining(Def);
     assert(I != LI.end() && "Missing segment for VNI");
-    if (I->end != VNI->def.getDeadSlot())
+
+    // Is the register live before? Otherwise we may have to add a read-undef
+    // flag for subregister defs.
+    if (MRI->tracksSubRegLiveness()) {
+      if ((I == LI.begin() || std::prev(I)->end < Def) && !VNI->isPHIDef()) {
+        MachineInstr *MI = getInstructionFromIndex(Def);
+        MI->addRegisterDefReadUndef(LI.reg);
+      }
+    }
+
+    if (I->end != Def.getDeadSlot())
       continue;
     if (VNI->isPHIDef()) {
       // This is a dead PHI. Remove it.
       VNI->markUnused();
       LI.removeSegment(I);
-      DEBUG(dbgs() << "Dead PHI at " << VNI->def << " may separate interval\n");
+      DEBUG(dbgs() << "Dead PHI at " << Def << " may separate interval\n");
       PHIRemoved = true;
     } else {
       // This is a dead def. Make sure the instruction knows.
-      MachineInstr *MI = getInstructionFromIndex(VNI->def);
+      MachineInstr *MI = getInstructionFromIndex(Def);
       assert(MI && "No instruction defining live value");
       MI->addRegisterDead(LI.reg, TRI);
       if (dead && MI->allDefsAreDead()) {
-        DEBUG(dbgs() << "All defs dead: " << VNI->def << '\t' << *MI);
+        DEBUG(dbgs() << "All defs dead: " << Def << '\t' << *MI);
         dead->push_back(MI);
       }
     }

diff --git a/lib/CodeGen/MachineInstr.cpp b/lib/CodeGen/MachineInstr.cpp
index 968ec2c68e8c9df50865c7f455d401c22efdd26d..470d6cbdb0546b62a706c7c349464fee385c6f49 100644 (file)
--- a/lib/CodeGen/MachineInstr.cpp
+++ b/lib/CodeGen/MachineInstr.cpp
@@ -1889,6 +1889,14 @@ bool MachineInstr::addRegisterDead(unsigned Reg,
   return true;
 }
 
+void MachineInstr::addRegisterDefReadUndef(unsigned Reg) {
+  for (MachineOperand &MO : operands()) {
+    if (!MO.isReg() || !MO.isDef() || MO.getReg() != Reg || MO.getSubReg() == 0)
+      continue;
+    MO.setIsUndef();
+  }
+}
+
 void MachineInstr::addRegisterDefined(unsigned Reg,
                                       const TargetRegisterInfo *RegInfo) {
   if (TargetRegisterInfo::isPhysicalRegister(Reg)) {