llvm/utils/TableGen/DAGISelEmitter.cpp

   1 //===- DAGISelEmitter.cpp - Generate an instruction selector --------------===//
   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 //
   9 // This tablegen backend emits a DAG instruction selector.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "Common/CodeGenDAGPatterns.h"
  14 #include "Common/CodeGenInstruction.h"
  15 #include "Common/CodeGenTarget.h"
  16 #include "Common/DAGISelMatcher.h"
  17 #include "llvm/Support/Debug.h"
  18 #include "llvm/TableGen/Record.h"
  19 #include "llvm/TableGen/TGTimer.h"
  20 #include "llvm/TableGen/TableGenBackend.h"
  21 using namespace llvm;
  22
  23 #define DEBUG_TYPE "dag-isel-emitter"
  24
  25 namespace {
  26 /// DAGISelEmitter - The top-level class which coordinates construction
  27 /// and emission of the instruction selector.
  28 class DAGISelEmitter {
  29   const RecordKeeper &Records; // Just so we can get at the timing functions.
  30   const CodeGenDAGPatterns CGP;
  31
  32 public:
  33   explicit DAGISelEmitter(const RecordKeeper &R) : Records(R), CGP(R) {}
  34   void run(raw_ostream &OS);
  35 };
  36 } // End anonymous namespace
  37
  38 //===----------------------------------------------------------------------===//
  39 // DAGISelEmitter Helper methods
  40 //
  41
  42 /// Compute the number of instructions for this pattern.
  43 /// This is a temporary hack.  We should really include the instruction
  44 /// latencies in this calculation.
  45 static unsigned getResultPatternCost(TreePatternNode &P,
  46                                      const CodeGenDAGPatterns &CGP) {
  47   if (P.isLeaf())
  48     return 0;
  49
  50   unsigned Cost = 0;
  51   const Record *Op = P.getOperator();
  52   if (Op->isSubClassOf("Instruction")) {
  53     Cost++;
  54     CodeGenInstruction &II = CGP.getTargetInfo().getInstruction(Op);
  55     if (II.usesCustomInserter)
  56       Cost += 10;
  57   }
  58   for (unsigned I = 0, E = P.getNumChildren(); I != E; ++I)
  59     Cost += getResultPatternCost(P.getChild(I), CGP);
  60   return Cost;
  61 }
  62
  63 /// getResultPatternCodeSize - Compute the code size of instructions for this
  64 /// pattern.
  65 static unsigned getResultPatternSize(TreePatternNode &P,
  66                                      const CodeGenDAGPatterns &CGP) {
  67   if (P.isLeaf())
  68     return 0;
  69
  70   unsigned Cost = 0;
  71   const Record *Op = P.getOperator();
  72   if (Op->isSubClassOf("Instruction")) {
  73     Cost += Op->getValueAsInt("CodeSize");
  74   }
  75   for (unsigned I = 0, E = P.getNumChildren(); I != E; ++I)
  76     Cost += getResultPatternSize(P.getChild(I), CGP);
  77   return Cost;
  78 }
  79
  80 namespace {
  81 // PatternSortingPredicate - return true if we prefer to match LHS before RHS.
  82 // In particular, we want to match maximal patterns first and lowest cost within
  83 // a particular complexity first.
  84 struct PatternSortingPredicate {
  85   PatternSortingPredicate(const CodeGenDAGPatterns &cgp) : CGP(cgp) {}
  86   const CodeGenDAGPatterns &CGP;
  87
  88   bool operator()(const PatternToMatch *LHS, const PatternToMatch *RHS) {
  89     const TreePatternNode &LT = LHS->getSrcPattern();
  90     const TreePatternNode &RT = RHS->getSrcPattern();
  91
  92     MVT LHSVT = LT.getNumTypes() != 0 ? LT.getSimpleType(0) : MVT::Other;
  93     MVT RHSVT = RT.getNumTypes() != 0 ? RT.getSimpleType(0) : MVT::Other;
  94     if (LHSVT.isVector() != RHSVT.isVector())
  95       return RHSVT.isVector();
  96
  97     if (LHSVT.isFloatingPoint() != RHSVT.isFloatingPoint())
  98       return RHSVT.isFloatingPoint();
  99
 100     // Otherwise, if the patterns might both match, sort based on complexity,
 101     // which means that we prefer to match patterns that cover more nodes in the
 102     // input over nodes that cover fewer.
 103     int LHSSize = LHS->getPatternComplexity(CGP);
 104     int RHSSize = RHS->getPatternComplexity(CGP);
 105     if (LHSSize > RHSSize)
 106       return true; // LHS -> bigger -> less cost
 107     if (LHSSize < RHSSize)
 108       return false;
 109
 110     // If the patterns have equal complexity, compare generated instruction cost
 111     unsigned LHSCost = getResultPatternCost(LHS->getDstPattern(), CGP);
 112     unsigned RHSCost = getResultPatternCost(RHS->getDstPattern(), CGP);
 113     if (LHSCost < RHSCost)
 114       return true;
 115     if (LHSCost > RHSCost)
 116       return false;
 117
 118     unsigned LHSPatSize = getResultPatternSize(LHS->getDstPattern(), CGP);
 119     unsigned RHSPatSize = getResultPatternSize(RHS->getDstPattern(), CGP);
 120     if (LHSPatSize < RHSPatSize)
 121       return true;
 122     if (LHSPatSize > RHSPatSize)
 123       return false;
 124
 125     // Sort based on the UID of the pattern, to reflect source order.
 126     // Note that this is not guaranteed to be unique, since a single source
 127     // pattern may have been resolved into multiple match patterns due to
 128     // alternative fragments.  To ensure deterministic output, always use
 129     // std::stable_sort with this predicate.
 130     return LHS->getID() < RHS->getID();
 131   }
 132 };
 133 } // End anonymous namespace
 134
 135 void DAGISelEmitter::run(raw_ostream &OS) {
 136   TGTimer &Timer = Records.getTimer();
 137   Timer.startTimer("Parse patterns");
 138   emitSourceFileHeader("DAG Instruction Selector for the " +
 139                            CGP.getTargetInfo().getName().str() + " target",
 140                        OS);
 141
 142   OS << "// *** NOTE: This file is #included into the middle of the target\n"
 143      << "// *** instruction selector class.  These functions are really "
 144      << "methods.\n\n";
 145
 146   OS << "// If GET_DAGISEL_DECL is #defined with any value, only function\n"
 147         "// declarations will be included when this file is included.\n"
 148         "// If GET_DAGISEL_BODY is #defined, its value should be the name of\n"
 149         "// the instruction selector class. Function bodies will be emitted\n"
 150         "// and each function's name will be qualified with the name of the\n"
 151         "// class.\n"
 152         "//\n"
 153         "// When neither of the GET_DAGISEL* macros is defined, the functions\n"
 154         "// are emitted inline.\n\n";
 155
 156   LLVM_DEBUG(errs() << "\n\nALL PATTERNS TO MATCH:\n\n";
 157              for (CodeGenDAGPatterns::ptm_iterator I = CGP.ptm_begin(),
 158                   E = CGP.ptm_end();
 159                   I != E; ++I) {
 160                errs() << "PATTERN: ";
 161                I->getSrcPattern().dump();
 162                errs() << "\nRESULT:  ";
 163                I->getDstPattern().dump();
 164                errs() << "\n";
 165              });
 166
 167   // Add all the patterns to a temporary list so we can sort them.
 168   Timer.startTimer("Sort patterns");
 169   std::vector<const PatternToMatch *> Patterns;
 170   for (const PatternToMatch &PTM : CGP.ptms())
 171     Patterns.push_back(&PTM);
 172
 173   // We want to process the matches in order of minimal cost.  Sort the patterns
 174   // so the least cost one is at the start.
 175   llvm::stable_sort(Patterns, PatternSortingPredicate(CGP));
 176
 177   // Convert each variant of each pattern into a Matcher.
 178   Timer.startTimer("Convert to matchers");
 179   SmallVector<Matcher *, 0> PatternMatchers;
 180   for (const PatternToMatch *PTM : Patterns) {
 181     for (unsigned Variant = 0;; ++Variant) {
 182       if (Matcher *M = ConvertPatternToMatcher(*PTM, Variant, CGP))
 183         PatternMatchers.push_back(M);
 184       else
 185         break;
 186     }
 187   }
 188
 189   std::unique_ptr<Matcher> TheMatcher =
 190       std::make_unique<ScopeMatcher>(std::move(PatternMatchers));
 191
 192   Timer.startTimer("Optimize matchers");
 193   OptimizeMatcher(TheMatcher, CGP);
 194
 195   // Matcher->dump();
 196
 197   Timer.startTimer("Emit matcher table");
 198   EmitMatcherTable(TheMatcher.get(), CGP, OS);
 199 }
 200
 201 static TableGen::Emitter::OptClass<DAGISelEmitter>
 202     X("gen-dag-isel", "Generate a DAG instruction selector");