[CleanUp] Remove NumInstructions field from LoopVectorizer's RegisterUsage struct.

[mattd]

Summary

This variable is largely going unused; aside from reporting number of instructions for in DEBUG builds.

The only use of NumInstructions is in debug output to represent the LoopSize. That value can be can be misleading as it also includes metadata instructions (e.g., DBG_VALUE) which have no real impact. If we do choose to keep this around, we probably should guard it by a DEBUG macro, as it's not used in production builds.

[rengolin]

The original code was calculating the unroll factor by NumInstructions like:

UF = std::min(UF, (32 / R.NumInstructions));

which has been replaced a long time ago, so yeah, left overs. :)

LGTM, thanks!

[mattd]

In D44495#1037956, @rengolin wrote:

The original code was calculating the unroll factor by NumInstructions like:

UF = std::min(UF, (32 / R.NumInstructions));

which has been replaced a long time ago, so yeah, left overs. :)

LGTM, thanks!

Great, thank you!

lib/Transforms/Vectorize/LoopVectorize.cpp

public:
   /// \brief A struct that represents some properties of the register usage
   /// of a loop.
   struct RegisterUsage {
     /// Holds the number of loop invariant values that are used in the loop.
     unsigned LoopInvariantRegs;
 
     /// Holds the maximum number of concurrent live intervals in the loop.
     unsigned MaxLocalUsers;
-
-    /// Holds the number of instructions in the loop.
-    unsigned NumInstructions;
   };
 
   /// \return Returns information about the register usages of the loop for the
   /// given vectorization factors.
   SmallVector<RegisterUsage, 8> calculateRegisterUsage(ArrayRef<unsigned> VFs);
 
   /// Collect values we want to ignore in the cost model.
   void collectValuesToIgnore();
if (VF == 1) {
     if (ForceTargetNumVectorRegs.getNumOccurrences() > 0)
       TargetNumRegisters = ForceTargetNumVectorRegs;
   }
 
   RegisterUsage R = calculateRegisterUsage({VF})[0];
   // We divide by these constants so assume that we have at least one
   // instruction that uses at least one register.
   R.MaxLocalUsers = std::max(R.MaxLocalUsers, 1U);
-  R.NumInstructions = std::max(R.NumInstructions, 1U);
 
   // We calculate the interleave count using the following formula.
   // Subtract the number of loop invariants from the number of available
   // registers. These registers are used by all of the interleaved instances.
   // Next, divide the remaining registers by the number of registers that is
   // required by the loop, in order to estimate how many parallel instances
   // fit without causing spills. All of this is rounded down if necessary to be
   // a power of two. We want power of two interleave count to simplify any
LoopVectorizationCostModel::calculateRegisterUsage(ArrayRef<unsigned> VFs) {
   // We also search for instructions that are defined outside the loop, but are
   // used inside the loop. We need this number separately from the max-interval
   // usage number because when we unroll, loop-invariant values do not take
   // more register.
   LoopBlocksDFS DFS(TheLoop);
   DFS.perform(LI);
 
   RegisterUsage RU;
-  RU.NumInstructions = 0;
 
   // Each 'key' in the map opens a new interval. The values
   // of the map are the index of the 'last seen' usage of the
   // instruction that is the key.
   using IntervalMap = DenseMap<Instruction *, unsigned>;
 
   // Maps instruction to its index.
   DenseMap<unsigned, Instruction *> IdxToInstr;
   // Marks the end of each interval.
   IntervalMap EndPoint;
   // Saves the list of instruction indices that are used in the loop.
   SmallSet<Instruction *, 8> Ends;
   // Saves the list of values that are used in the loop but are
   // defined outside the loop, such as arguments and constants.
   SmallPtrSet<Value *, 8> LoopInvariants;
 
   unsigned Index = 0;
   for (BasicBlock *BB : make_range(DFS.beginRPO(), DFS.endRPO())) {
-    RU.NumInstructions += BB->size();
     for (Instruction &I : *BB) {
       IdxToInstr[Index++] = &I;
 
       // Save the end location of each USE.
       for (Value *U : I.operands()) {
         auto *Instr = dyn_cast<Instruction>(U);
 
         // Ignore non-instruction values such as arguments, constants, etc.
for (unsigned i = 0, e = VFs.size(); i < e; ++i) {
     else {
       for (auto Inst : LoopInvariants)
         Invariant += GetRegUsage(Inst->getType(), VFs[i]);
     }
 
     DEBUG(dbgs() << "LV(REG): VF = " << VFs[i] << '\n');
     DEBUG(dbgs() << "LV(REG): Found max usage: " << MaxUsages[i] << '\n');
     DEBUG(dbgs() << "LV(REG): Found invariant usage: " << Invariant << '\n');
-    DEBUG(dbgs() << "LV(REG): LoopSize: " << RU.NumInstructions << '\n');
 
     RU.LoopInvariantRegs = Invariant;
     RU.MaxLocalUsers = MaxUsages[i];
     RUs[i] = RU;
   }
 
   return RUs;
 }