1 //===-- TargetSelect.cpp - Target Chooser Code ----------------------------===//
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 just asks the TargetRegistry for the appropriate target to use, and
10 // allows the user to specify a specific one on the commandline with -march=x,
11 // -mcpu=y, and -mattr=a,-b,+c. Clients should initialize targets prior to
12 // calling selectTarget().
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "llvm/ADT/Triple.h"
17 #include "llvm/ExecutionEngine/ExecutionEngine.h"
18 #include "llvm/IR/Module.h"
19 #include "llvm/MC/SubtargetFeature.h"
20 #include "llvm/MC/TargetRegistry.h"
21 #include "llvm/Support/Host.h"
22 #include "llvm/Target/TargetMachine.h"
23 
24 using namespace llvm;
25 
26 TargetMachine *EngineBuilder::selectTarget() {
27   Triple TT;
28 
29   // MCJIT can generate code for remote targets, but the old JIT and Interpreter
30   // must use the host architecture.
31   if (WhichEngine != EngineKind::Interpreter && M)
32     TT.setTriple(M->getTargetTriple());
33 
34   return selectTarget(TT, MArch, MCPU, MAttrs);
35 }
36 
37 /// selectTarget - Pick a target either via -march or by guessing the native
38 /// arch.  Add any CPU features specified via -mcpu or -mattr.
39 TargetMachine *EngineBuilder::selectTarget(const Triple &TargetTriple,
40                               StringRef MArch,
41                               StringRef MCPU,
42                               const SmallVectorImpl<std::string>& MAttrs) {
43   Triple TheTriple(TargetTriple);
44   if (TheTriple.getTriple().empty())
45     TheTriple.setTriple(sys::getProcessTriple());
46 
47   // Adjust the triple to match what the user requested.
48   const Target *TheTarget = nullptr;
49   if (!MArch.empty()) {
50     auto I = find_if(TargetRegistry::targets(),
51                      [&](const Target &T) { return MArch == T.getName(); });
52 
53     if (I == TargetRegistry::targets().end()) {
54       if (ErrorStr)
55         *ErrorStr = "No available targets are compatible with this -march, "
56                     "see -version for the available targets.\n";
57       return nullptr;
58     }
59 
60     TheTarget = &*I;
61 
62     // Adjust the triple to match (if known), otherwise stick with the
63     // requested/host triple.
64     Triple::ArchType Type = Triple::getArchTypeForLLVMName(MArch);
65     if (Type != Triple::UnknownArch)
66       TheTriple.setArch(Type);
67   } else {
68     std::string Error;
69     TheTarget = TargetRegistry::lookupTarget(TheTriple.getTriple(), Error);
70     if (!TheTarget) {
71       if (ErrorStr)
72         *ErrorStr = Error;
73       return nullptr;
74     }
75   }
76 
77   // Package up features to be passed to target/subtarget
78   std::string FeaturesStr;
79   if (!MAttrs.empty()) {
80     SubtargetFeatures Features;
81     for (unsigned i = 0; i != MAttrs.size(); ++i)
82       Features.AddFeature(MAttrs[i]);
83     FeaturesStr = Features.getString();
84   }
85 
86   // Allocate a target...
87   TargetMachine *Target =
88       TheTarget->createTargetMachine(TheTriple.getTriple(), MCPU, FeaturesStr,
89                                      Options, RelocModel, CMModel, OptLevel,
90 				     /*JIT*/ true);
91   Target->Options.EmulatedTLS = EmulatedTLS;
92   Target->Options.ExplicitEmulatedTLS = true;
93 
94   assert(Target && "Could not allocate target machine!");
95   return Target;
96 }
97