Home | History | Annotate | Line # | Download | only in MCA 
      1 //===--------------------- Support.cpp --------------------------*- C++ -*-===//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 /// \file
      9 ///
     10 /// This file implements a few helper functions used by various pipeline
     11 /// components.
     12 ///
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "llvm/MCA/Support.h"
     16 #include "llvm/MC/MCSchedule.h"
     17 
     18 namespace llvm {
     19 namespace mca {
     20 
     21 #define DEBUG_TYPE "llvm-mca"
     22 
     23 ResourceCycles &ResourceCycles::operator+=(const ResourceCycles &RHS) {
     24   if (Denominator == RHS.Denominator)
     25     Numerator += RHS.Numerator;
     26   else {
     27     // Create a common denominator for LHS and RHS by calculating the least
     28     // common multiple from the GCD.
     29     unsigned GCD = GreatestCommonDivisor64(Denominator, RHS.Denominator);
     30     unsigned LCM = (Denominator * RHS.Denominator) / GCD;
     31     unsigned LHSNumerator = Numerator * (LCM / Denominator);
     32     unsigned RHSNumerator = RHS.Numerator * (LCM / RHS.Denominator);
     33     Numerator = LHSNumerator + RHSNumerator;
     34     Denominator = LCM;
     35   }
     36   return *this;
     37 }
     38 
     39 void computeProcResourceMasks(const MCSchedModel &SM,
     40                               MutableArrayRef<uint64_t> Masks) {
     41   unsigned ProcResourceID = 0;
     42 
     43   assert(Masks.size() == SM.getNumProcResourceKinds() &&
     44          "Invalid number of elements");
     45   // Resource at index 0 is the 'InvalidUnit'. Set an invalid mask for it.
     46   Masks[0] = 0;
     47 
     48   // Create a unique bitmask for every processor resource unit.
     49   for (unsigned I = 1, E = SM.getNumProcResourceKinds(); I < E; ++I) {
     50     const MCProcResourceDesc &Desc = *SM.getProcResource(I);
     51     if (Desc.SubUnitsIdxBegin)
     52       continue;
     53     Masks[I] = 1ULL << ProcResourceID;
     54     ProcResourceID++;
     55   }
     56 
     57   // Create a unique bitmask for every processor resource group.
     58   for (unsigned I = 1, E = SM.getNumProcResourceKinds(); I < E; ++I) {
     59     const MCProcResourceDesc &Desc = *SM.getProcResource(I);
     60     if (!Desc.SubUnitsIdxBegin)
     61       continue;
     62     Masks[I] = 1ULL << ProcResourceID;
     63     for (unsigned U = 0; U < Desc.NumUnits; ++U) {
     64       uint64_t OtherMask = Masks[Desc.SubUnitsIdxBegin[U]];
     65       Masks[I] |= OtherMask;
     66     }
     67     ProcResourceID++;
     68   }
     69 
     70 #ifndef NDEBUG
     71   LLVM_DEBUG(dbgs() << "\nProcessor resource masks:"
     72                     << "\n");
     73   for (unsigned I = 0, E = SM.getNumProcResourceKinds(); I < E; ++I) {
     74     const MCProcResourceDesc &Desc = *SM.getProcResource(I);
     75     LLVM_DEBUG(dbgs() << '[' << format_decimal(I,2) << "] " << " - "
     76                       << format_hex(Masks[I],16) << " - "
     77                       << Desc.Name << '\n');
     78   }
     79 #endif
     80 }
     81 
     82 double computeBlockRThroughput(const MCSchedModel &SM, unsigned DispatchWidth,
     83                                unsigned NumMicroOps,
     84                                ArrayRef<unsigned> ProcResourceUsage) {
     85   // The block throughput is bounded from above by the hardware dispatch
     86   // throughput. That is because the DispatchWidth is an upper bound on the
     87   // number of opcodes that can be part of a single dispatch group.
     88   double Max = static_cast<double>(NumMicroOps) / DispatchWidth;
     89 
     90   // The block throughput is also limited by the amount of hardware parallelism.
     91   // The number of available resource units affects the resource pressure
     92   // distribution, as well as how many blocks can be executed every cycle.
     93   for (unsigned I = 0, E = SM.getNumProcResourceKinds(); I < E; ++I) {
     94     unsigned ResourceCycles = ProcResourceUsage[I];
     95     if (!ResourceCycles)
     96       continue;
     97 
     98     const MCProcResourceDesc &MCDesc = *SM.getProcResource(I);
     99     double Throughput = static_cast<double>(ResourceCycles) / MCDesc.NumUnits;
    100     Max = std::max(Max, Throughput);
    101   }
    102 
    103   // The block reciprocal throughput is computed as the MAX of:
    104   //  - (NumMicroOps / DispatchWidth)
    105   //  - (NumUnits / ResourceCycles)   for every consumed processor resource.
    106   return Max;
    107 }
    108 
    109 } // namespace mca
    110 } // namespace llvm
    111