[lli] Make lli support -mcpu=native for CPU autodetection

[craig.topper]

Summary

llc, opt, and clang can all autodetect the CPU and supported features. lli cannot as far as I could tell.

This patch uses the getCPUStr() and introduces a new getCPUFeatureList() and uses those in lli in place of MCPU and MAttrs.

Ideally, we should merge getCPUFeatureList and getCPUFeatureStr, but opt and llc need a string and lli wanted a list. Maybe we should just return the SubtargetFeature object and let the caller decide what it needs?

[davide]

This change looks fine, but can you add a unit test (if possible)?

[craig.topper]

Do you have any suggestions of how to do that? Not sure what features I could guarantee from the build bots.

[davide]

hmm, native makes this a pain. Probably not worth the trouble.

llvm/trunk/include/llvm/CodeGen/CommandFlags.def

LLVM_ATTRIBUTE_UNUSED static std::string getFeaturesStr() {
   }
 
   for (unsigned i = 0; i != MAttrs.size(); ++i)
     Features.AddFeature(MAttrs[i]);
 
   return Features.getString();
 }
 
+LLVM_ATTRIBUTE_UNUSED static std::vector<std::string> getFeatureList() {
+  SubtargetFeatures Features;
+
+  // If user asked for the 'native' CPU, we need to autodetect features.
+  // This is necessary for x86 where the CPU might not support all the
+  // features the autodetected CPU name lists in the target. For example,
+  // not all Sandybridge processors support AVX.
+  if (MCPU == "native") {
+    StringMap<bool> HostFeatures;
+    if (sys::getHostCPUFeatures(HostFeatures))
+      for (auto &F : HostFeatures)
+        Features.AddFeature(F.first(), F.second);
+  }
+
+  for (unsigned i = 0; i != MAttrs.size(); ++i)
+    Features.AddFeature(MAttrs[i]);
+
+  return Features.getFeatures();
+}
+
 /// \brief Set function attributes of functions in Module M based on CPU,
 /// Features, and command line flags.
 LLVM_ATTRIBUTE_UNUSED static void
 setFunctionAttributes(StringRef CPU, StringRef Features, Module &M) {
   for (auto &F : M) {
     auto &Ctx = F.getContext();
     AttributeList Attrs = F.getAttributes();
     AttrBuilder NewAttrs;

llvm/trunk/tools/lli/lli.cpp

if (NoLazyCompilation) {
     ExitOnError ExitOnErr(std::string(*argv) +
                           ": bitcode didn't read correctly: ");
     ExitOnErr(Mod->materializeAll());
   }
 
   std::string ErrorMsg;
   EngineBuilder builder(std::move(Owner));
   builder.setMArch(MArch);
-  builder.setMCPU(MCPU);
-  builder.setMAttrs(MAttrs);
+  builder.setMCPU(getCPUStr());
+  builder.setMAttrs(getFeatureList());
   if (RelocModel.getNumOccurrences())
     builder.setRelocationModel(RelocModel);
   if (CMModel.getNumOccurrences())
     builder.setCodeModel(CMModel);
   builder.setErrorStr(&ErrorMsg);
   builder.setEngineKind(ForceInterpreter
                         ? EngineKind::Interpreter
                         : EngineKind::JIT);