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      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/Support/Host.h"
     21 #include "llvm/Support/TargetRegistry.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