Subzero: Ignore variables with no actual uses.

src/IceOperand.cpp

 //===- subzero/src/IceOperand.cpp - High-level operand implementation -----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 238 matching lines @@
   // A phi source variable conservatively needs to be marked as multi-block,
   // even if its definition is in the same block. This is because there can be
   // additional control flow before branching back to this node, and the
   // variable is live throughout those nodes.
   if (Instr && llvm::isa<InstPhi>(Instr))
     MakeMulti = true;
 
   if (!MakeMulti) {
     switch (MultiBlock) {
     case MBS_Unknown:
+    case MBS_NoUses:
       MultiBlock = MBS_SingleBlock;
       SingleUseNode = Node;
       break;
     case MBS_SingleBlock:
       if (SingleUseNode != Node)
         MakeMulti = true;
       break;
     case MBS_MultiBlock:
       break;
     }
@@ skipping 94 matching lines @@
     assert(FirstOrSingleDefinition);
     return FirstOrSingleDefinition;
   }
   return nullptr;
 }
 
 void VariablesMetadata::init(MetadataKind TrackingKind) {
   TimerMarker T(TimerStack::TT_vmetadata, Func);
   Kind = TrackingKind;
   Metadata.clear();
-  Metadata.resize(Func->getNumVariables());
+  Metadata.resize(Func->getNumVariables(), VariableTracking::MBS_NoUses);
 
   // Mark implicit args as being used in the entry node.
   for (Variable *Var : Func->getImplicitArgs()) {
     constexpr Inst *NoInst = nullptr;
     CfgNode *EntryNode = Func->getEntryNode();
     constexpr bool IsImplicit = true;
     Metadata[Var->getIndex()].markUse(Kind, NoInst, EntryNode, IsImplicit);
   }
 
   for (CfgNode *Node : Func->getNodes())
@@ skipping 48 matching lines @@
   if (!isTracked(Var))
     return true; // conservative answer
   SizeT VarNum = Var->getIndex();
   // Conservatively return true if the state is unknown.
   return Metadata[VarNum].getMultiDef() != VariableTracking::MDS_SingleDef;
 }
 
 bool VariablesMetadata::isMultiBlock(const Variable *Var) const {
   if (Var->getIsArg())
     return true;
+  if (Var->isRematerializable())
+    return false;
   if (!isTracked(Var))
     return true; // conservative answer
   SizeT VarNum = Var->getIndex();
+  switch (Metadata[VarNum].getMultiBlock()) {
+  case VariableTracking::MBS_NoUses:
+  case VariableTracking::MBS_SingleBlock:
+    return false;
   // Conservatively return true if the state is unknown.
-  return Metadata[VarNum].getMultiBlock() != VariableTracking::MBS_SingleBlock;
+  case VariableTracking::MBS_Unknown:
+  case VariableTracking::MBS_MultiBlock:
+    return true;
+  }
+  assert(0);
+  return true;
+}
+
+bool VariablesMetadata::isSingleBlock(const Variable *Var) const {
+  if (Var->getIsArg())
+    return false;
+  if (Var->isRematerializable())
+    return false;
+  if (!isTracked(Var))
+    return false; // conservative answer
+  SizeT VarNum = Var->getIndex();
+  switch (Metadata[VarNum].getMultiBlock()) {
+  case VariableTracking::MBS_SingleBlock:
+    return true;
+  case VariableTracking::MBS_Unknown:
+  case VariableTracking::MBS_NoUses:
+  case VariableTracking::MBS_MultiBlock:
+    return false;
+  }
+  assert(0);
+  return false;
 }
 
 const Inst *
 VariablesMetadata::getFirstDefinitionSingleBlock(const Variable *Var) const {
   assert(Kind != VMK_Uses);
   if (!isTracked(Var))
     return nullptr; // conservative answer
   SizeT VarNum = Var->getIndex();
   return Metadata[VarNum].getFirstDefinitionSingleBlock();
 }
@@ skipping 162 matching lines @@
   if (getType() != IceType_i32 && getType() != IceType_i16 &&
       getType() != IceType_i8)
     return false;
   // The Following checks if the signed representation of Value is between
   // -Threshold/2 and +Threshold/2
   bool largerThanThreshold = Threshold / 2 + Value >= Threshold;
   return largerThanThreshold;
 }
 
 } // end of namespace Ice