1 //===- SubtargetFeature.cpp - CPU characteristics Implementation ----------===//
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 /// \file Implements the SubtargetFeature interface.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/MC/SubtargetFeature.h"
14 #include "llvm/ADT/ArrayRef.h"
15 #include "llvm/ADT/SmallVector.h"
16 #include "llvm/ADT/StringExtras.h"
17 #include "llvm/ADT/StringRef.h"
18 #include "llvm/ADT/Triple.h"
19 #include "llvm/Config/llvm-config.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 FeatureBitset &Implies,
126                     ArrayRef<SubtargetFeatureKV> FeatureTable) {
127   // OR the Implies bits in outside the loop. This allows the Implies for CPUs
128   // which might imply features not in FeatureTable to use this.
129   Bits |= Implies;
130   for (const SubtargetFeatureKV &FE : FeatureTable)
131     if (Implies.test(FE.Value))
132       SetImpliedBits(Bits, FE.Implies.getAsBitset(), FeatureTable);
133 }
134 
135 /// For each feature that (transitively) implies this feature, clear it.
136 static
137 void ClearImpliedBits(FeatureBitset &Bits, unsigned Value,
138                       ArrayRef<SubtargetFeatureKV> FeatureTable) {
139   for (const SubtargetFeatureKV &FE : FeatureTable) {
140     if (FE.Implies.getAsBitset().test(Value)) {
141       Bits.reset(FE.Value);
142       ClearImpliedBits(Bits, FE.Value, FeatureTable);
143     }
144   }
145 }
146 
147 void
148 SubtargetFeatures::ToggleFeature(FeatureBitset &Bits, StringRef Feature,
149                                  ArrayRef<SubtargetFeatureKV> FeatureTable) {
150   // Find feature in table.
151   const SubtargetFeatureKV *FeatureEntry =
152       Find(StripFlag(Feature), FeatureTable);
153   // If there is a match
154   if (FeatureEntry) {
155     if (Bits.test(FeatureEntry->Value)) {
156       Bits.reset(FeatureEntry->Value);
157       // For each feature that implies this, clear it.
158       ClearImpliedBits(Bits, FeatureEntry->Value, FeatureTable);
159     } else {
160       Bits.set(FeatureEntry->Value);
161 
162       // For each feature that this implies, set it.
163       SetImpliedBits(Bits, FeatureEntry->Implies.getAsBitset(), FeatureTable);
164     }
165   } else {
166     errs() << "'" << Feature << "' is not a recognized feature for this target"
167            << " (ignoring feature)\n";
168   }
169 }
170 
171 void SubtargetFeatures::ApplyFeatureFlag(FeatureBitset &Bits, StringRef Feature,
172                                     ArrayRef<SubtargetFeatureKV> FeatureTable) {
173   assert(hasFlag(Feature));
174 
175   // Find feature in table.
176   const SubtargetFeatureKV *FeatureEntry =
177       Find(StripFlag(Feature), FeatureTable);
178   // If there is a match
179   if (FeatureEntry) {
180     // Enable/disable feature in bits
181     if (isEnabled(Feature)) {
182       Bits.set(FeatureEntry->Value);
183 
184       // For each feature that this implies, set it.
185       SetImpliedBits(Bits, FeatureEntry->Implies.getAsBitset(), FeatureTable);
186     } else {
187       Bits.reset(FeatureEntry->Value);
188 
189       // For each feature that implies this, clear it.
190       ClearImpliedBits(Bits, FeatureEntry->Value, FeatureTable);
191     }
192   } else {
193     errs() << "'" << Feature << "' is not a recognized feature for this target"
194            << " (ignoring feature)\n";
195   }
196 }
197 
198 FeatureBitset
199 SubtargetFeatures::getFeatureBits(StringRef CPU,
200                                   ArrayRef<SubtargetFeatureKV> CPUTable,
201                                   ArrayRef<SubtargetFeatureKV> FeatureTable) {
202   if (CPUTable.empty() || FeatureTable.empty())
203     return FeatureBitset();
204 
205   assert(std::is_sorted(std::begin(CPUTable), std::end(CPUTable)) &&
206          "CPU table is not sorted");
207   assert(std::is_sorted(std::begin(FeatureTable), std::end(FeatureTable)) &&
208          "CPU features table is not sorted");
209   // Resulting bits
210   FeatureBitset Bits;
211 
212   // Check if help is needed
213   if (CPU == "help")
214     Help(CPUTable, FeatureTable);
215 
216   // Find CPU entry if CPU name is specified.
217   else if (!CPU.empty()) {
218     const SubtargetFeatureKV *CPUEntry = Find(CPU, CPUTable);
219 
220     // If there is a match
221     if (CPUEntry) {
222       // Set the features implied by this CPU feature, if any.
223       SetImpliedBits(Bits, CPUEntry->Implies.getAsBitset(), FeatureTable);
224     } else {
225       errs() << "'" << CPU << "' is not a recognized processor for this target"
226              << " (ignoring processor)\n";
227     }
228   }
229 
230   // Iterate through each feature
231   for (const std::string &Feature : Features) {
232     // Check for help
233     if (Feature == "+help")
234       Help(CPUTable, FeatureTable);
235     else
236       ApplyFeatureFlag(Bits, Feature, FeatureTable);
237   }
238 
239   return Bits;
240 }
241 
242 void SubtargetFeatures::print(raw_ostream &OS) const {
243   for (auto &F : Features)
244     OS << F << " ";
245   OS << "\n";
246 }
247 
248 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
249 LLVM_DUMP_METHOD void SubtargetFeatures::dump() const {
250   print(dbgs());
251 }
252 #endif
253 
254 void SubtargetFeatures::getDefaultSubtargetFeatures(const Triple& Triple) {
255   // FIXME: This is an inelegant way of specifying the features of a
256   // subtarget. It would be better if we could encode this information
257   // into the IR. See <rdar://5972456>.
258   if (Triple.getVendor() == Triple::Apple) {
259     if (Triple.getArch() == Triple::ppc) {
260       // powerpc-apple-*
261       AddFeature("altivec");
262     } else if (Triple.getArch() == Triple::ppc64) {
263       // powerpc64-apple-*
264       AddFeature("64bit");
265       AddFeature("altivec");
266     }
267   }
268 }
269