Add a flag to indicate that an instruction is as cheap (or cheaper) than a move

instruction to execute. This can be used for transformations (like two-address
conversion) to remat an instruction instead of generating a "move"
instruction. The idea is to decrease the live ranges and register pressure and
all that jazz.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51660 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetInstrDesc.h

@@ -95,7 +95,8 @@ namespace TID {
     Commutable,
     ConvertibleTo3Addr,
     UsesCustomDAGSchedInserter,
-    Rematerializable
+    Rematerializable,
+    CheapAsAMove
   };
 }
 
@@ -387,6 +388,15 @@ public:
   bool isRematerializable() const {
     return Flags & (1 << TID::Rematerializable);
   }
+
+  /// isAsCheapAsAMove - Returns true if this instruction has the same cost (or
+  /// less) than a move instruction. This is useful during certain types of
+  /// rematerializations (e.g., during two-address conversion) where we would
+  /// like to remat the instruction, but not if it costs more than moving the
+  /// instruction into the appropriate register.
+  bool isAsCheapAsAMove() const {
+    return Flags & (1 << TID::CheapAsAMove);
+  }
 };
 
 } // end namespace llvm

lib/CodeGen/MachineInstr.cpp

@@ -639,9 +639,9 @@ void MachineInstr::copyPredicates(const MachineInstr *MI) {
   }
 }
 
-/// isSafeToMove - Return true if it is safe to this instruction. If SawStore
-/// true, it means there is a store (or call) between the instruction the
-/// localtion and its intended destination.
+/// isSafeToMove - Return true if it is safe to this instruction. If SawStore is
+/// set to true, it means that there is a store (or call) between the
+/// instruction's location and its intended destination.
 bool MachineInstr::isSafeToMove(const TargetInstrInfo *TII, bool &SawStore) {
   // Ignore stuff that we obviously can't move.
   if (TID->mayStore() || TID->isCall()) {

lib/Target/Target.td

@@ -203,22 +203,25 @@ class Instruction {
   bit usesCustomDAGSchedInserter = 0; // Pseudo instr needing special help.
   bit hasCtrlDep   = 0;     // Does this instruction r/w ctrl-flow chains?
   bit isNotDuplicable = 0;  // Is it unsafe to duplicate this instruction?
+  bit isAsCheapAsAMove = 0; // As cheap (or cheaper) than a move instruction.
 
   // Side effect flags - When set, the flags have these meanings:
   //
   //  hasSideEffects - The instruction has side effects that are not
   //    captured by any operands of the instruction or other flags.
+  //
   //  mayHaveSideEffects  - Some instances of the instruction can have side
   //    effects. The virtual method "isReallySideEffectFree" is called to
   //    determine this. Load instructions are an example of where this is
   //    useful. In general, loads always have side effects. However, loads from
   //    constant pools don't. Individual back ends make this determination.
+  //
   //  neverHasSideEffects - Set on an instruction with no pattern if it has no
   //    side effects.
   bit hasSideEffects = 0;
   bit mayHaveSideEffects = 0;
   bit neverHasSideEffects = 0;
-  
+
   InstrItinClass Itinerary = NoItinerary;// Execution steps used for scheduling.
 
   string Constraints = "";  // OperandConstraint, e.g. $src = $dst.

utils/TableGen/CodeGenInstruction.cpp

@@ -99,6 +99,7 @@ CodeGenInstruction::CodeGenInstruction(Record *R, const std::string &AsmStr)
   hasSideEffects = R->getValueAsBit("hasSideEffects");
   mayHaveSideEffects = R->getValueAsBit("mayHaveSideEffects");
   neverHasSideEffects = R->getValueAsBit("neverHasSideEffects");
+  isAsCheapAsAMove = R->getValueAsBit("isAsCheapAsAMove");
   hasOptionalDef = false;
   isVariadic = false;
 

utils/TableGen/CodeGenInstruction.h

@@ -102,7 +102,10 @@ namespace llvm {
     bool hasCtrlDep;
     bool isNotDuplicable;
     bool hasOptionalDef;
-    bool hasSideEffects, mayHaveSideEffects, neverHasSideEffects;
+    bool hasSideEffects;
+    bool mayHaveSideEffects;
+    bool neverHasSideEffects;
+    bool isAsCheapAsAMove;
     
     /// ParseOperandName - Parse an operand name like "$foo" or "$foo.bar",
     /// where $foo is a whole operand and $foo.bar refers to a suboperand.

utils/TableGen/InstrInfoEmitter.cpp

@@ -208,26 +208,27 @@ void InstrInfoEmitter::emitRecord(const CodeGenInstruction &Inst, unsigned Num,
      << ",\t\"" << Inst.TheDef->getName() << "\", 0";
 
   // Emit all of the target indepedent flags...
-  if (Inst.isReturn)     OS << "|(1<<TID::Return)";
-  if (Inst.isBranch)     OS << "|(1<<TID::Branch)";
-  if (Inst.isIndirectBranch) OS << "|(1<<TID::IndirectBranch)";
-  if (Inst.isBarrier)    OS << "|(1<<TID::Barrier)";
-  if (Inst.hasDelaySlot) OS << "|(1<<TID::DelaySlot)";
-  if (Inst.isCall)       OS << "|(1<<TID::Call)";
-  if (Inst.isSimpleLoad) OS << "|(1<<TID::SimpleLoad)";
-  if (Inst.mayLoad)      OS << "|(1<<TID::MayLoad)";
-  if (Inst.mayStore)     OS << "|(1<<TID::MayStore)";
-  if (Inst.isPredicable) OS << "|(1<<TID::Predicable)";
+  if (Inst.isReturn)           OS << "|(1<<TID::Return)";
+  if (Inst.isBranch)           OS << "|(1<<TID::Branch)";
+  if (Inst.isIndirectBranch)   OS << "|(1<<TID::IndirectBranch)";
+  if (Inst.isBarrier)          OS << "|(1<<TID::Barrier)";
+  if (Inst.hasDelaySlot)       OS << "|(1<<TID::DelaySlot)";
+  if (Inst.isCall)             OS << "|(1<<TID::Call)";
+  if (Inst.isSimpleLoad)       OS << "|(1<<TID::SimpleLoad)";
+  if (Inst.mayLoad)            OS << "|(1<<TID::MayLoad)";
+  if (Inst.mayStore)           OS << "|(1<<TID::MayStore)";
+  if (Inst.isPredicable)       OS << "|(1<<TID::Predicable)";
   if (Inst.isConvertibleToThreeAddress) OS << "|(1<<TID::ConvertibleTo3Addr)";
-  if (Inst.isCommutable) OS << "|(1<<TID::Commutable)";
-  if (Inst.isTerminator) OS << "|(1<<TID::Terminator)";
+  if (Inst.isCommutable)       OS << "|(1<<TID::Commutable)";
+  if (Inst.isTerminator)       OS << "|(1<<TID::Terminator)";
   if (Inst.isReMaterializable) OS << "|(1<<TID::Rematerializable)";
   if (Inst.isNotDuplicable)    OS << "|(1<<TID::NotDuplicable)";
   if (Inst.hasOptionalDef)     OS << "|(1<<TID::HasOptionalDef)";
   if (Inst.usesCustomDAGSchedInserter)
     OS << "|(1<<TID::UsesCustomDAGSchedInserter)";
   if (Inst.isVariadic)         OS << "|(1<<TID::Variadic)";
-  if (Inst.hasSideEffects)          OS << "|(1<<TID::UnmodeledSideEffects)";
+  if (Inst.hasSideEffects)     OS << "|(1<<TID::UnmodeledSideEffects)";
+  if (Inst.isAsCheapAsAMove)   OS << "|(1<<TID::CheapAsAMove)";
   OS << ", 0";
 
   // Emit all of the target-specific flags...