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