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      1 //===-- TargetSelect.cpp - Target Chooser Code ----------------------------===//
      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 // This just asks the TargetRegistry for the appropriate target to use, and
     11 // allows the user to specify a specific one on the commandline with -march=x,
     12 // -mcpu=y, and -mattr=a,-b,+c. Clients should initialize targets prior to
     13 // calling selectTarget().
     14 //
     15 //===----------------------------------------------------------------------===//
     16 
     17 #include "llvm/ExecutionEngine/ExecutionEngine.h"
     18 #include "llvm/ADT/Triple.h"
     19 #include "llvm/IR/Module.h"
     20 #include "llvm/MC/SubtargetFeature.h"
     21 #include "llvm/Support/CommandLine.h"
     22 #include "llvm/Support/Host.h"
     23 #include "llvm/Support/TargetRegistry.h"
     24 #include "llvm/Target/TargetMachine.h"
     25 
     26 using namespace llvm;
     27 
     28 TargetMachine *EngineBuilder::selectTarget() {
     29   Triple TT;
     30 
     31   // MCJIT can generate code for remote targets, but the old JIT and Interpreter
     32   // must use the host architecture.
     33   if (WhichEngine != EngineKind::Interpreter && M)
     34     TT.setTriple(M->getTargetTriple());
     35 
     36   return selectTarget(TT, MArch, MCPU, MAttrs);
     37 }
     38 
     39 /// selectTarget - Pick a target either via -march or by guessing the native
     40 /// arch.  Add any CPU features specified via -mcpu or -mattr.
     41 TargetMachine *EngineBuilder::selectTarget(const Triple &TargetTriple,
     42                               StringRef MArch,
     43                               StringRef MCPU,
     44                               const SmallVectorImpl<std::string>& MAttrs) {
     45   Triple TheTriple(TargetTriple);
     46   if (TheTriple.getTriple().empty())
     47     TheTriple.setTriple(sys::getProcessTriple());
     48 
     49   // Adjust the triple to match what the user requested.
     50   const Target *TheTarget = nullptr;
     51   if (!MArch.empty()) {
     52     auto I = std::find_if(
     53         TargetRegistry::targets().begin(), TargetRegistry::targets().end(),
     54         [&](const Target &T) { return MArch == T.getName(); });
     55 
     56     if (I == TargetRegistry::targets().end()) {
     57       if (ErrorStr)
     58         *ErrorStr = "No available targets are compatible with this -march, "
     59                     "see -version for the available targets.\n";
     60       return nullptr;
     61     }
     62 
     63     TheTarget = &*I;
     64 
     65     // Adjust the triple to match (if known), otherwise stick with the
     66     // requested/host triple.
     67     Triple::ArchType Type = Triple::getArchTypeForLLVMName(MArch);
     68     if (Type != Triple::UnknownArch)
     69       TheTriple.setArch(Type);
     70   } else {
     71     std::string Error;
     72     TheTarget = TargetRegistry::lookupTarget(TheTriple.getTriple(), Error);
     73     if (!TheTarget) {
     74       if (ErrorStr)
     75         *ErrorStr = Error;
     76       return nullptr;
     77     }
     78   }
     79 
     80   // Package up features to be passed to target/subtarget
     81   std::string FeaturesStr;
     82   if (!MAttrs.empty()) {
     83     SubtargetFeatures Features;
     84     for (unsigned i = 0; i != MAttrs.size(); ++i)
     85       Features.AddFeature(MAttrs[i]);
     86     FeaturesStr = Features.getString();
     87   }
     88 
     89   // FIXME: non-iOS ARM FastISel is broken with MCJIT.
     90   if (TheTriple.getArch() == Triple::arm &&
     91       !TheTriple.isiOS() &&
     92       OptLevel == CodeGenOpt::None) {
     93     OptLevel = CodeGenOpt::Less;
     94   }
     95 
     96   // Allocate a target...
     97   TargetMachine *Target = TheTarget->createTargetMachine(TheTriple.getTriple(),
     98                                                          MCPU, FeaturesStr,
     99                                                          Options,
    100                                                          RelocModel, CMModel,
    101                                                          OptLevel);
    102   assert(Target && "Could not allocate target machine!");
    103   return Target;
    104 }
    105