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 "llvm/Support/Debug.h"
18#include <numeric>
19
20namespace llvm {
21namespace mca {
22
23#define DEBUG_TYPE "llvm-mca"
24
25ReleaseAtCycles &ReleaseAtCycles::operator+=(const ReleaseAtCycles &RHS) {
26 if (Denominator == RHS.Denominator)
27 Numerator += RHS.Numerator;
28 else {
29 // Create a common denominator for LHS and RHS by calculating the least
30 // common multiple from the GCD.
31 unsigned GCD = std::gcd(m: Denominator, n: RHS.Denominator);
32 unsigned LCM = (Denominator * RHS.Denominator) / GCD;
33 unsigned LHSNumerator = Numerator * (LCM / Denominator);
34 unsigned RHSNumerator = RHS.Numerator * (LCM / RHS.Denominator);
35 Numerator = LHSNumerator + RHSNumerator;
36 Denominator = LCM;
37 }
38 return *this;
39}
40
41void computeProcResourceMasks(const MCSchedModel &SM,
42 MutableArrayRef<uint64_t> Masks) {
43 unsigned ProcResourceID = 0;
44
45 assert(Masks.size() == SM.getNumProcResourceKinds() &&
46 "Invalid number of elements");
47 // Resource at index 0 is the 'InvalidUnit'. Set an invalid mask for it.
48 Masks[0] = 0;
49
50 // Create a unique bitmask for every processor resource unit.
51 for (unsigned I = 1, E = SM.getNumProcResourceKinds(); I < E; ++I) {
52 const MCProcResourceDesc &Desc = *SM.getProcResource(ProcResourceIdx: I);
53 if (Desc.SubUnitsIdxBegin)
54 continue;
55 Masks[I] = 1ULL << ProcResourceID;
56 ProcResourceID++;
57 }
58
59 // Create a unique bitmask for every processor resource group.
60 for (unsigned I = 1, E = SM.getNumProcResourceKinds(); I < E; ++I) {
61 const MCProcResourceDesc &Desc = *SM.getProcResource(ProcResourceIdx: I);
62 if (!Desc.SubUnitsIdxBegin)
63 continue;
64 Masks[I] = 1ULL << ProcResourceID;
65 for (unsigned U = 0; U < Desc.NumUnits; ++U) {
66 uint64_t OtherMask = Masks[Desc.SubUnitsIdxBegin[U]];
67 Masks[I] |= OtherMask;
68 }
69 ProcResourceID++;
70 }
71}
72
73#ifndef NDEBUG
74void dumpProcResourceMasks(const MCSchedModel &SM, ArrayRef<uint64_t> Masks) {
75 dbgs() << "\nProcessor resource masks:\n";
76 for (unsigned I = 0, E = SM.getNumProcResourceKinds(); I < E; ++I) {
77 const MCProcResourceDesc &Desc = *SM.getProcResource(I);
78 dbgs() << '[' << format_decimal(I, 2) << "] " << " - "
79 << format_hex(Masks[I], 16) << " - " << Desc.Name << '\n';
80 }
81}
82#endif
83
84double computeBlockRThroughput(const MCSchedModel &SM, unsigned DispatchWidth,
85 unsigned NumMicroOps,
86 ArrayRef<unsigned> ProcResourceUsage) {
87 // The block throughput is bounded from above by the hardware dispatch
88 // throughput. That is because the DispatchWidth is an upper bound on the
89 // number of opcodes that can be part of a single dispatch group.
90 double Max = static_cast<double>(NumMicroOps) / DispatchWidth;
91
92 // The block throughput is also limited by the amount of hardware parallelism.
93 // The number of available resource units affects the resource pressure
94 // distribution, as well as how many blocks can be executed every cycle.
95 for (unsigned I = 0, E = SM.getNumProcResourceKinds(); I < E; ++I) {
96 unsigned ReleaseAtCycles = ProcResourceUsage[I];
97 if (!ReleaseAtCycles)
98 continue;
99
100 const MCProcResourceDesc &MCDesc = *SM.getProcResource(ProcResourceIdx: I);
101 double Throughput = static_cast<double>(ReleaseAtCycles) / MCDesc.NumUnits;
102 Max = std::max(a: Max, b: Throughput);
103 }
104
105 // The block reciprocal throughput is computed as the MAX of:
106 // - (NumMicroOps / DispatchWidth)
107 // - (NumUnits / ReleaseAtCycles) for every consumed processor resource.
108 return Max;
109}
110
111} // namespace mca
112} // namespace llvm
113