Fix a bunch of pessimizing moves which prevent copy elision.

Author: dcci

lib/ClangImporter/ImporterImpl.h

@@ -1214,7 +1214,7 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
     SmallVector<ProtocolConformance *, 4> result
       = std::move(conformances->second);
     DelayedConformances.erase(conformances);
-    return std::move(result);
+    return result;
   }
 
   /// Record the set of imported protocols for the given declaration,

lib/Driver/Driver.cpp

@@ -1377,7 +1377,7 @@ Driver::buildOutputFileMap(const llvm::opt::DerivedArgList &Args) const {
     // TODO: emit diagnostic with error string
     Diags.diagnose(SourceLoc(), diag::error_unable_to_load_output_file_map);
   }
-  return std::move(OFM);
+  return OFM;
 }
 
 void Driver::buildJobs(const ActionList &Actions, const OutputInfo &OI,

lib/IDE/Utils.cpp

@@ -174,7 +174,7 @@ ide::isSourceInputComplete(std::unique_ptr<llvm::MemoryBuffer> MemBuf) {
       break;
   }
   if (!IndentInfos.empty()) {
-    SCR.IndentPrefix = std::move(IndentInfos.back().Prefix.str());
+    SCR.IndentPrefix = IndentInfos.back().Prefix.str();
     // Trim off anything that follows a non-space character
     const size_t pos = SCR.IndentPrefix.find_first_not_of(" \t");
     if (pos != std::string::npos)

lib/SILGen/SILGenApply.cpp

@@ -3208,7 +3208,7 @@ namespace {
       // Reassign ArgValue.
       RValue NewRValue = RValue(gen, ArgLoc, ArgTy.getSwiftRValueType(),
                                  ArgManagedValue);
-      ArgValue = std::move(ArgumentSource(ArgLoc, std::move(NewRValue)));
+      ArgValue = ArgumentSource(ArgLoc, std::move(NewRValue));
     }
   };
 

lib/SILGen/SILGenProlog.cpp

@@ -96,7 +96,7 @@ class EmitBBArguments : public CanTypeVisitor<EmitBBArguments,
       // An unowned parameter is passed at +0, like guaranteed, but it isn't
       // kept alive by the caller, so we need to retain and manage it
       // regardless.
-      return std::move(gen.emitManagedRetain(loc, arg));
+      return gen.emitManagedRetain(loc, arg);
 
     case ParameterConvention::Indirect_Inout:
     case ParameterConvention::Indirect_InoutAliasable:

tools/swift-ide-test/ModuleAPIDiff.cpp

@@ -730,7 +730,7 @@ class SMAModelGenerator : public DeclVisitor<SMAModelGenerator> {
     sma::TypeName ResultTN;
     llvm::raw_string_ostream OS(ResultTN.Name);
     T.print(OS, Options);
-    return std::move(ResultTN);
+    return ResultTN;
   }
 
   llvm::Optional<sma::TypeName> convertToOptionalTypeName(Type T) const {