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