Subzero: Slight improvement to phi lowering.

src/IceCfgNode.cpp

 //===- subzero/src/IceCfgNode.cpp - Basic block (node) implementation -----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 562 matching lines @@
     // Guess that the number of live ranges beginning is roughly the
     // number of instructions, and same for live ranges ending.
     LiveBegin->reserve(getInstCountEstimate());
     LiveEnd->reserve(getInstCountEstimate());
   }
   // Initialize Live to be the union of all successors' LiveIn.
   for (CfgNode *Succ : OutEdges) {
     Live |= Liveness->getLiveIn(Succ);
     // Mark corresponding argument of phis in successor as live.
     for (Inst &I : Succ->Phis) {
+      if (I.isDeleted())
+        continue;
       auto Phi = llvm::dyn_cast<InstPhi>(&I);
       Phi->livenessPhiOperand(Live, this, Liveness);
     }
   }
   Liveness->getLiveOut(this) = Live;
 
   // Process regular instructions in reverse order.
   for (Inst &I : reverse_range(Insts)) {
     if (I.isDeleted())
       continue;
@@ skipping 98 matching lines @@
     // the Variable's live range begins and ends in this block.  If
     // i1<i2, then i1's live range begins at instruction IBB->second
     // and extends through the end of the block.  If i1>i2, then i2's
     // live range begins at the first instruction of the block and
     // ends at IEB->second.  In any case, we choose the lesser of i1
     // and i2 and proceed accordingly.
     InstNumberT LB = i == i1 ? IBB->second : FirstInstNum;
     InstNumberT LE = i == i2 ? IEB->second : LastInstNum + 1;
 
     Variable *Var = Liveness->getVariable(i, this);
     if (!Var->getIgnoreLiveness()) {

[jvoung (off chromium), 2015/08/05 19:32:26]

There was also this getIgnoreLiveness, but that sounds like a "permanent"
property of the variable, compared to the RangeMask.

[Jim Stichnoth, 2015/08/05 23:18:54]

That's true.  But it seems like I could set it up so that RangeMask[V]=false
when V->getIgnoreLiveness() is true, such that V would never even be added to
LiveBegin/LiveEnd.  I added a TODO for a follow-on CL.

       if (LB > LE) {
         Var->addLiveRange(FirstInstNum, LE, 1);
         Var->addLiveRange(LB, LastInstNum + 1, 1);
         // Assert that Var is a global variable by checking that its
         // liveness index is less than the number of globals.  This
         // ensures that the LiveInAndOut[] access is valid.
         assert(i < Liveness->getNumGlobalVars());
         LiveInAndOut[i] = false;
       } else {
         Var->addLiveRange(LB, LE, 1);
       }
     }
     if (i == i1)
       ++IBB;
     if (i == i2)
       ++IEB;
   }
   // Process the variables that are live across the entire block.
   for (int i = LiveInAndOut.find_first(); i != -1;
        i = LiveInAndOut.find_next(i)) {
     Variable *Var = Liveness->getVariable(i, this);
-    Var->addLiveRange(FirstInstNum, LastInstNum + 1, 1);
+    if (Liveness->getRangeMask(Var->getIndex()))
+      Var->addLiveRange(FirstInstNum, LastInstNum + 1, 1);
   }
 }
 
 // If this node contains only deleted instructions, and ends in an
 // unconditional branch, contract the node by repointing all its
 // in-edges to its successor.
 void CfgNode::contractIfEmpty() {
   if (InEdges.empty())
     return;
   Inst *Branch = nullptr;
@@ skipping 543 matching lines @@
   InstIntrinsicCall *Inst = InstIntrinsicCall::create(
       Func, 5, Func->makeVariable(IceType_i64), RMWI64Name, Info->Info);
   Inst->addArg(AtomicRMWOp);
   Inst->addArg(Counter);
   Inst->addArg(One);
   Inst->addArg(OrderAcquireRelease);
   Insts.push_front(Inst);
 }
 
 } // end of namespace Ice