Teach PHI elimination to remove REG_SEQUENCE instructions and update references of the source operands with references of the destination with subreg indices. e.g.

%reg1029<def>, %reg1030<def> = VLD1q16 %reg1024<kill>, ...
%reg1031<def> = REG_SEQUENCE %reg1029<kill>, 5, %reg1030<kill>, 6
=>
%reg1031:5<def>, %reg1031:6<def> = VLD1q16 %reg1024<kill>, ...

PHI elimination now does more than phi elimination. It is really a de-SSA pass.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103039 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveIntervalAnalysis.cpp

@@ -262,6 +262,23 @@ static void printRegName(unsigned reg, const TargetRegisterInfo* tri_) {
 }
 #endif
 
+static
+bool MultipleDefsByMI(const MachineInstr &MI, unsigned MOIdx) {
+  unsigned Reg = MI.getOperand(MOIdx).getReg();
+  for (unsigned i = MOIdx+1, e = MI.getNumOperands(); i < e; ++i) {
+    const MachineOperand &MO = MI.getOperand(i);
+    if (!MO.isReg())
+      continue;
+    if (MO.getReg() == Reg && MO.isDef()) {
+      assert(MI.getOperand(MOIdx).getSubReg() != MO.getSubReg() &&
+             MI.getOperand(MOIdx).getSubReg() &&
+             MO.getSubReg());
+      return true;
+    }
+  }
+  return false;
+}
+
 void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
                                              MachineBasicBlock::iterator mi,
                                              SlotIndex MIIdx,
@@ -372,6 +389,13 @@ void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
     }
 
   } else {
+    if (MultipleDefsByMI(*mi, MOIdx))
+      // Mutple defs of the same virtual register by the same instruction. e.g.
+      // %reg1031:5<def>, %reg1031:6<def> = VLD1q16 %reg1024<kill>, ...
+      // This is likely due to elimination of REG_SEQUENCE instructions. Return
+      // here since there is nothing to do.
+      return;
+
     // If this is the second time we see a virtual register definition, it
     // must be due to phi elimination or two addr elimination.  If this is
     // the result of two address elimination, then the vreg is one of the