[Cleanup] Utility function to erase instruction and mark DBG_Values

[Gerolf]

Summary

New function to erase a machine instruction and mark DBG_VALUE
for removal. A DBG_VALUE is marked for removal when it references
an operand defined in the instruction.
Use the new function to cleanup code in dead machine instruction
removal pass.

[dblaikie]

Looks great - thanks!

[Gerolf]

Thanks for your review!
Committed revision 215580.

Cheers,
Gerolf

include/llvm/CodeGen/MachineInstr.h

public:
 
   /// Unlink 'this' from the containing basic block and delete it.
   ///
   /// If this instruction is the header of a bundle, the whole bundle is erased.
   /// This function can not be used for instructions inside a bundle, use
   /// eraseFromBundle() to erase individual bundled instructions.
   void eraseFromParent();
 
+  /// Unlink 'this' from the containing basic block and delete it.
+  ///
+  /// For all definitions mark their uses in DBG_VALUE nodes
+  /// as undefined. Otherwise like eraseFromParent().
+  void eraseFromParentAndMarkDBGValuesForRemoval();
+
   /// Unlink 'this' form its basic block and delete it.
   ///
   /// If the instruction is part of a bundle, the other instructions in the
   /// bundle remain bundled.
   void eraseFromBundle();
 
   bool isEHLabel() const { return getOpcode() == TargetOpcode::EH_LABEL; }
   bool isGCLabel() const { return getOpcode() == TargetOpcode::GC_LABEL; }

lib/CodeGen/DeadMachineInstructionElim.cpp

for (MachineFunction::reverse_iterator I = MF.rbegin(), E = MF.rend();
     for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(),
          MIE = MBB->rend(); MII != MIE; ) {
       MachineInstr *MI = &*MII;
 
       // If the instruction is dead, delete it!
       if (isDead(MI)) {
         DEBUG(dbgs() << "DeadMachineInstructionElim: DELETING: " << *MI);
         // It is possible that some DBG_VALUE instructions refer to this
-        // instruction.  Examine each def operand for such references;
-        // if found, mark the DBG_VALUE as undef (but don't delete it).
-        for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
-          const MachineOperand &MO = MI->getOperand(i);
-          if (!MO.isReg() || !MO.isDef())
-            continue;
-          unsigned Reg = MO.getReg();
-          if (!TargetRegisterInfo::isVirtualRegister(Reg))
-            continue;
-          MRI->markUsesInDebugValueAsUndef(Reg);
-        }
+        // instruction.  They get marked as undef and will be deleted
+        // in the live debug variable analysis.
+        MI->eraseFromParentAndMarkDBGValuesForRemoval();
         AnyChanges = true;
-        MI->eraseFromParent();
         ++NumDeletes;
         MIE = MBB->rend();
         // MII is now pointing to the next instruction to process,
         // so don't increment it.
         continue;
       }
 
       // Record the physreg defs.

lib/CodeGen/MachineInstr.cpp

MachineInstr *MachineInstr::removeFromBundle() {
   return getParent()->remove_instr(this);
 }
 
 void MachineInstr::eraseFromParent() {
   assert(getParent() && "Not embedded in a basic block!");
   getParent()->erase(this);
 }
 
+void MachineInstr::eraseFromParentAndMarkDBGValuesForRemoval() {
+  assert(getParent() && "Not embedded in a basic block!");
+  MachineBasicBlock *MBB = getParent();
+  MachineFunction *MF = MBB->getParent();
+  assert(MF && "Not embedded in a function!");
+
+  MachineInstr *MI = (MachineInstr *)this;
+  MachineRegisterInfo &MRI = MF->getRegInfo();
+
+  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (!MO.isReg() || !MO.isDef())
+      continue;
+    unsigned Reg = MO.getReg();
+    if (!TargetRegisterInfo::isVirtualRegister(Reg))
+      continue;
+    MRI.markUsesInDebugValueAsUndef(Reg);
+  }
+  MI->eraseFromParent();
+}
+
 void MachineInstr::eraseFromBundle() {
   assert(getParent() && "Not embedded in a basic block!");
   getParent()->erase_instr(this);
 }
 
 /// getNumExplicitOperands - Returns the number of non-implicit operands.
 ///
 unsigned MachineInstr::getNumExplicitOperands() const {