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
19namespace llvm {
20namespace mca {
21
22#define DEBUG_TYPE "llvm-mca"
23
24ReleaseAtCycles &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(m: Denominator, n: 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
40void 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(ProcResourceIdx: 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(ProcResourceIdx: 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
83double 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(ProcResourceIdx: I);
100 double Throughput = static_cast<double>(ReleaseAtCycles) / MCDesc.NumUnits;
101 Max = std::max(a: Max, b: 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