1 //===- SubtargetFeature.cpp - CPU characteristics Implementation ----------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 /// \file Implements the SubtargetFeature interface.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/MC/SubtargetFeature.h"
15 #include "llvm/ADT/ArrayRef.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/StringExtras.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/ADT/Triple.h"
20 #include "llvm/Support/Compiler.h"
21 #include "llvm/Support/Debug.h"
22 #include "llvm/Support/Format.h"
23 #include "llvm/Support/raw_ostream.h"
24 #include <algorithm>
25 #include <cassert>
26 #include <cstddef>
27 #include <cstring>
28 #include <iterator>
29 #include <string>
30 #include <vector>
31 
32 using namespace llvm;
33 
34 /// Determine if a feature has a flag; '+' or '-'
35 static inline bool hasFlag(StringRef Feature) {
36   assert(!Feature.empty() && "Empty string");
37   // Get first character
38   char Ch = Feature[0];
39   // Check if first character is '+' or '-' flag
40   return Ch == '+' || Ch =='-';
41 }
42 
43 /// Return string stripped of flag.
44 static inline std::string StripFlag(StringRef Feature) {
45   return hasFlag(Feature) ? Feature.substr(1) : Feature;
46 }
47 
48 /// Return true if enable flag; '+'.
49 static inline bool isEnabled(StringRef Feature) {
50   assert(!Feature.empty() && "Empty string");
51   // Get first character
52   char Ch = Feature[0];
53   // Check if first character is '+' for enabled
54   return Ch == '+';
55 }
56 
57 /// Splits a string of comma separated items in to a vector of strings.
58 static void Split(std::vector<std::string> &V, StringRef S) {
59   SmallVector<StringRef, 3> Tmp;
60   S.split(Tmp, ',', -1, false /* KeepEmpty */);
61   V.assign(Tmp.begin(), Tmp.end());
62 }
63 
64 void SubtargetFeatures::AddFeature(StringRef String, bool Enable) {
65   // Don't add empty features.
66   if (!String.empty())
67     // Convert to lowercase, prepend flag if we don't already have a flag.
68     Features.push_back(hasFlag(String) ? String.lower()
69                                        : (Enable ? "+" : "-") + String.lower());
70 }
71 
72 /// Find KV in array using binary search.
73 static const SubtargetFeatureKV *Find(StringRef S,
74                                       ArrayRef<SubtargetFeatureKV> A) {
75   // Binary search the array
76   auto F = std::lower_bound(A.begin(), A.end(), S);
77   // If not found then return NULL
78   if (F == A.end() || StringRef(F->Key) != S) return nullptr;
79   // Return the found array item
80   return F;
81 }
82 
83 /// Return the length of the longest entry in the table.
84 static size_t getLongestEntryLength(ArrayRef<SubtargetFeatureKV> Table) {
85   size_t MaxLen = 0;
86   for (auto &I : Table)
87     MaxLen = std::max(MaxLen, std::strlen(I.Key));
88   return MaxLen;
89 }
90 
91 /// Display help for feature choices.
92 static void Help(ArrayRef<SubtargetFeatureKV> CPUTable,
93                  ArrayRef<SubtargetFeatureKV> FeatTable) {
94   // Determine the length of the longest CPU and Feature entries.
95   unsigned MaxCPULen  = getLongestEntryLength(CPUTable);
96   unsigned MaxFeatLen = getLongestEntryLength(FeatTable);
97 
98   // Print the CPU table.
99   errs() << "Available CPUs for this target:\n\n";
100   for (auto &CPU : CPUTable)
101     errs() << format("  %-*s - %s.\n", MaxCPULen, CPU.Key, CPU.Desc);
102   errs() << '\n';
103 
104   // Print the Feature table.
105   errs() << "Available features for this target:\n\n";
106   for (auto &Feature : FeatTable)
107     errs() << format("  %-*s - %s.\n", MaxFeatLen, Feature.Key, Feature.Desc);
108   errs() << '\n';
109 
110   errs() << "Use +feature to enable a feature, or -feature to disable it.\n"
111             "For example, llc -mcpu=mycpu -mattr=+feature1,-feature2\n";
112 }
113 
114 SubtargetFeatures::SubtargetFeatures(StringRef Initial) {
115   // Break up string into separate features
116   Split(Features, Initial);
117 }
118 
119 std::string SubtargetFeatures::getString() const {
120   return join(Features.begin(), Features.end(), ",");
121 }
122 
123 /// For each feature that is (transitively) implied by this feature, set it.
124 static
125 void SetImpliedBits(FeatureBitset &Bits, const SubtargetFeatureKV &FeatureEntry,
126                     ArrayRef<SubtargetFeatureKV> FeatureTable) {
127   for (const SubtargetFeatureKV &FE : FeatureTable) {
128     if (FeatureEntry.Value == FE.Value) continue;
129 
130     if ((FeatureEntry.Implies & FE.Value).any()) {
131       Bits |= FE.Value;
132       SetImpliedBits(Bits, FE, FeatureTable);
133     }
134   }
135 }
136 
137 /// For each feature that (transitively) implies this feature, clear it.
138 static
139 void ClearImpliedBits(FeatureBitset &Bits,
140                       const SubtargetFeatureKV &FeatureEntry,
141                       ArrayRef<SubtargetFeatureKV> FeatureTable) {
142   for (const SubtargetFeatureKV &FE : FeatureTable) {
143     if (FeatureEntry.Value == FE.Value) continue;
144 
145     if ((FE.Implies & FeatureEntry.Value).any()) {
146       Bits &= ~FE.Value;
147       ClearImpliedBits(Bits, FE, FeatureTable);
148     }
149   }
150 }
151 
152 void
153 SubtargetFeatures::ToggleFeature(FeatureBitset &Bits, StringRef Feature,
154                                  ArrayRef<SubtargetFeatureKV> FeatureTable) {
155   // Find feature in table.
156   const SubtargetFeatureKV *FeatureEntry =
157       Find(StripFlag(Feature), FeatureTable);
158   // If there is a match
159   if (FeatureEntry) {
160     if ((Bits & FeatureEntry->Value) == FeatureEntry->Value) {
161       Bits &= ~FeatureEntry->Value;
162       // For each feature that implies this, clear it.
163       ClearImpliedBits(Bits, *FeatureEntry, FeatureTable);
164     } else {
165       Bits |=  FeatureEntry->Value;
166 
167       // For each feature that this implies, set it.
168       SetImpliedBits(Bits, *FeatureEntry, FeatureTable);
169     }
170   } else {
171     errs() << "'" << Feature << "' is not a recognized feature for this target"
172            << " (ignoring feature)\n";
173   }
174 }
175 
176 void SubtargetFeatures::ApplyFeatureFlag(FeatureBitset &Bits, StringRef Feature,
177                                     ArrayRef<SubtargetFeatureKV> FeatureTable) {
178   assert(hasFlag(Feature));
179 
180   // Find feature in table.
181   const SubtargetFeatureKV *FeatureEntry =
182       Find(StripFlag(Feature), FeatureTable);
183   // If there is a match
184   if (FeatureEntry) {
185     // Enable/disable feature in bits
186     if (isEnabled(Feature)) {
187       Bits |= FeatureEntry->Value;
188 
189       // For each feature that this implies, set it.
190       SetImpliedBits(Bits, *FeatureEntry, FeatureTable);
191     } else {
192       Bits &= ~FeatureEntry->Value;
193 
194       // For each feature that implies this, clear it.
195       ClearImpliedBits(Bits, *FeatureEntry, FeatureTable);
196     }
197   } else {
198     errs() << "'" << Feature << "' is not a recognized feature for this target"
199            << " (ignoring feature)\n";
200   }
201 }
202 
203 FeatureBitset
204 SubtargetFeatures::getFeatureBits(StringRef CPU,
205                                   ArrayRef<SubtargetFeatureKV> CPUTable,
206                                   ArrayRef<SubtargetFeatureKV> FeatureTable) {
207   if (CPUTable.empty() || FeatureTable.empty())
208     return FeatureBitset();
209 
210   assert(std::is_sorted(std::begin(CPUTable), std::end(CPUTable)) &&
211          "CPU table is not sorted");
212   assert(std::is_sorted(std::begin(FeatureTable), std::end(FeatureTable)) &&
213          "CPU features table is not sorted");
214   // Resulting bits
215   FeatureBitset Bits;
216 
217   // Check if help is needed
218   if (CPU == "help")
219     Help(CPUTable, FeatureTable);
220 
221   // Find CPU entry if CPU name is specified.
222   else if (!CPU.empty()) {
223     const SubtargetFeatureKV *CPUEntry = Find(CPU, CPUTable);
224 
225     // If there is a match
226     if (CPUEntry) {
227       // Set base feature bits
228       Bits = CPUEntry->Value;
229 
230       // Set the feature implied by this CPU feature, if any.
231       for (auto &FE : FeatureTable) {
232         if ((CPUEntry->Value & FE.Value).any())
233           SetImpliedBits(Bits, FE, FeatureTable);
234       }
235     } else {
236       errs() << "'" << CPU << "' is not a recognized processor for this target"
237              << " (ignoring processor)\n";
238     }
239   }
240 
241   // Iterate through each feature
242   for (const std::string &Feature : Features) {
243     // Check for help
244     if (Feature == "+help")
245       Help(CPUTable, FeatureTable);
246 
247     ApplyFeatureFlag(Bits, Feature, FeatureTable);
248   }
249 
250   return Bits;
251 }
252 
253 void SubtargetFeatures::print(raw_ostream &OS) const {
254   for (auto &F : Features)
255     OS << F << " ";
256   OS << "\n";
257 }
258 
259 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
260 LLVM_DUMP_METHOD void SubtargetFeatures::dump() const {
261   print(dbgs());
262 }
263 #endif
264 
265 void SubtargetFeatures::getDefaultSubtargetFeatures(const Triple& Triple) {
266   // FIXME: This is an inelegant way of specifying the features of a
267   // subtarget. It would be better if we could encode this information
268   // into the IR. See <rdar://5972456>.
269   if (Triple.getVendor() == Triple::Apple) {
270     if (Triple.getArch() == Triple::ppc) {
271       // powerpc-apple-*
272       AddFeature("altivec");
273     } else if (Triple.getArch() == Triple::ppc64) {
274       // powerpc64-apple-*
275       AddFeature("64bit");
276       AddFeature("altivec");
277     }
278   }
279 }
280