[Target] Make a copy of TargetOptions feature list before sorting during CodeGen

[craig.topper]

Summary

Currently CodeGen is calling std::sort on the features vector in TargetOptions for every function, but I don't think CodeGen should be modifying TargetOptions.

This patch makes a copy before sorting.

[echristo]

This seems strictly more difficult to keep under control? Though I guess the assert helps.

Feel free to go ahead, but...

[craig.topper]

Yeah don't like it either, but was surprised to find that CodeGen even had a non-const reference to TargetOptions. Would it be better to make a copy and sort the copy during CodeGen?

[echristo]

No strong opinion. I think I like that one more though.

[craig.topper]

Make a copy before sorting and combine some repeated code that this exposed.

lib/CodeGen/CGCall.cpp

bool DisableTailCalls =
                         TargetDecl->hasAttr<AnyX86InterruptAttr>()));
     FuncAttrs.addAttribute("disable-tail-calls",
                            llvm::toStringRef(DisableTailCalls));
 
     // Add target-cpu and target-features attributes to functions. If
     // we have a decl for the function and it has a target attribute then
     // parse that and add it to the feature set.
     StringRef TargetCPU = getTarget().getTargetOpts().CPU;
+    std::vector<std::string> Features;
     const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(TargetDecl);
     if (FD && FD->hasAttr<TargetAttr>()) {
       llvm::StringMap<bool> FeatureMap;
       getFunctionFeatureMap(FeatureMap, FD);
 
       // Produce the canonical string for this set of features.
-      std::vector<std::string> Features;
       for (llvm::StringMap<bool>::const_iterator it = FeatureMap.begin(),
                                                  ie = FeatureMap.end();
            it != ie; ++it)
         Features.push_back((it->second ? "+" : "-") + it->first().str());
 
       // Now add the target-cpu and target-features to the function.
       // While we populated the feature map above, we still need to
       // get and parse the target attribute so we can get the cpu for
       // the function.
       const auto *TD = FD->getAttr<TargetAttr>();
       TargetAttr::ParsedTargetAttr ParsedAttr = TD->parse();
       if (ParsedAttr.Architecture != "" &&
           getTarget().isValidCPUName(ParsedAttr.Architecture))
         TargetCPU = ParsedAttr.Architecture;
-      if (TargetCPU != "")
-         FuncAttrs.addAttribute("target-cpu", TargetCPU);
-      if (!Features.empty()) {
-        std::sort(Features.begin(), Features.end());
-        FuncAttrs.addAttribute(
-            "target-features",
-            llvm::join(Features, ","));
-      }
     } else {
       // Otherwise just add the existing target cpu and target features to the
       // function.
-      std::vector<std::string> &Features = getTarget().getTargetOpts().Features;
-      if (TargetCPU != "")
-        FuncAttrs.addAttribute("target-cpu", TargetCPU);
-      if (!Features.empty()) {
-        std::sort(Features.begin(), Features.end());
-        FuncAttrs.addAttribute(
-            "target-features",
-            llvm::join(Features, ","));
-      }
-    }
-  }
+      Features = getTarget().getTargetOpts().Features;
+    }
+
 
   ClangToLLVMArgMapping IRFunctionArgs(getContext(), FI);
 
   QualType RetTy = FI.getReturnType();
   const ABIArgInfo &RetAI = FI.getReturnInfo();
   switch (RetAI.getKind()) {
   case ABIArgInfo::Extend:
     if (RetTy->hasSignedIntegerRepresentation())