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