lib/MCA/Support.cpp

   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