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
112