[clang-tidy][NFC] IdentifierNaming: Remove unnecessary string allocations

[njames93]

Summary

Remove the need to heap allocate a string for each style option lookup while reading or writing options.p

[aaron.ballman]

Was this caused by a performance concern when profiling something? I'm not opposed to the changes, but I do think the original formulation is easier to read.

[njames93]

In D90244#2357130, @aaron.ballman wrote:

Was this caused by a performance concern when profiling something? I'm not opposed to the changes, but I do think the original formulation is easier to read.

It's not a huge performance concern, but removing up to 156 malloc calls* for each time we read** or store the style is certainly reason for this.

*Depends on standard library implementations small string optimisation buffer size.
**Happens multiple times as of 4888c9ce.

[aaron.ballman]

In D90244#2357510, @njames93 wrote:

In D90244#2357130, @aaron.ballman wrote:

Was this caused by a performance concern when profiling something? I'm not opposed to the changes, but I do think the original formulation is easier to read.

It's not a huge performance concern, but removing up to 156 malloc calls* for each time we read** or store the style is certainly reason for this.

*Depends on standard library implementations small string optimisation buffer size.
**Happens multiple times as of 4888c9ce.

Okay, that's sufficiently motivating to me. Thank you, LGTM!

clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp

 #undef STRINGIZE
 };
 
 #undef NAMING_KEYS
 // clang-format on
 
 static std::vector<llvm::Optional<IdentifierNamingCheck::NamingStyle>>
 getNamingStyles(const ClangTidyCheck::OptionsView &Options) {
-  std::vector<llvm::Optional<IdentifierNamingCheck::NamingStyle>> Styles;
-  Styles.reserve(array_lengthof(StyleNames));
-  for (auto const &StyleName : StyleNames) {
-    auto CaseOptional = Options.getOptional<IdentifierNamingCheck::CaseType>(
-        (StyleName + "Case").str());
-    auto Prefix = Options.get((StyleName + "Prefix").str(), "");
-    auto Postfix = Options.get((StyleName + "Suffix").str(), "");
+  std::vector<llvm::Optional<IdentifierNamingCheck::NamingStyle>> Styles(
+      SK_Count);
+  SmallString<64> StyleString;
+  for (unsigned I = 0; I < SK_Count; ++I) {
+    StyleString = StyleNames[I];
+    size_t StyleSize = StyleString.size();
+    StyleString.append("Prefix");
+    std::string Prefix(Options.get(StyleString, ""));
+    // Fast replacement of [Pre]fix -> [Suf]fix.
+    memcpy(&StyleString[StyleSize], "Suf", 3);
+    std::string Postfix(Options.get(StyleString, ""));
+    memcpy(&StyleString[StyleSize], "Case", 4);
+    StyleString.pop_back();
+    StyleString.pop_back();
+    auto CaseOptional =
+        Options.getOptional<IdentifierNamingCheck::CaseType>(StyleString);
 
     if (CaseOptional || !Prefix.empty() || !Postfix.empty())
-      Styles.emplace_back(IdentifierNamingCheck::NamingStyle{
-          std::move(CaseOptional), std::move(Prefix), std::move(Postfix)});
-    else
-      Styles.emplace_back(llvm::None);
+      Styles[I].emplace(std::move(CaseOptional), std::move(Prefix),
+                        std::move(Postfix));
   }
   return Styles;
 }
 
 IdentifierNamingCheck::IdentifierNamingCheck(StringRef Name,
                                              ClangTidyContext *Context)
     : RenamerClangTidyCheck(Name, Context), Context(Context), CheckName(Name),
       GetConfigPerFile(Options.get("GetConfigPerFile", true)),
       IgnoreFailedSplit(Options.get("IgnoreFailedSplit", false)),
       IgnoreMainLikeFunctions(Options.get("IgnoreMainLikeFunctions", false)) {
 
   auto IterAndInserted = NamingStylesCache.try_emplace(
       llvm::sys::path::parent_path(Context->getCurrentFile()),
       getNamingStyles(Options));
   assert(IterAndInserted.second && "Couldn't insert Style");
   // Holding a reference to the data in the vector is safe as it should never
   // move.
   MainFileStyle = IterAndInserted.first->getValue();
 }
 
 IdentifierNamingCheck::~IdentifierNamingCheck() = default;
 
 void IdentifierNamingCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
   RenamerClangTidyCheck::storeOptions(Opts);
-  ArrayRef<llvm::Optional<NamingStyle>> NamingStyles =
-      getStyleForFile(Context->getCurrentFile());
+  SmallString<64> StyleString;
   for (size_t I = 0; I < SK_Count; ++I) {
-    if (!NamingStyles[I])
+    if (!MainFileStyle[I])
       continue;
-    if (NamingStyles[I]->Case)
-      Options.store(Opts, (StyleNames[I] + "Case").str(),
-                    *NamingStyles[I]->Case);
-    Options.store(Opts, (StyleNames[I] + "Prefix").str(),
-                  NamingStyles[I]->Prefix);
-    Options.store(Opts, (StyleNames[I] + "Suffix").str(),
-                  NamingStyles[I]->Suffix);
+    StyleString = StyleNames[I];
+    size_t StyleSize = StyleString.size();
+    StyleString.append("Prefix");
+    Options.store(Opts, StyleString, MainFileStyle[I]->Prefix);
+    // Fast replacement of [Pre]fix -> [Suf]fix.
+    memcpy(&StyleString[StyleSize], "Suf", 3);
+    Options.store(Opts, StyleString, MainFileStyle[I]->Suffix);
+    if (MainFileStyle[I]->Case) {
+      memcpy(&StyleString[StyleSize], "Case", 4);
+      StyleString.pop_back();
+      StyleString.pop_back();
+      Options.store(Opts, StyleString, *MainFileStyle[I]->Case);
+    }
   }
   Options.store(Opts, "GetConfigPerFile", GetConfigPerFile);
   Options.store(Opts, "IgnoreFailedSplit", IgnoreFailedSplit);
   Options.store(Opts, "IgnoreMainLikeFunctions", IgnoreMainLikeFunctions);
 }
 
 static bool matchesStyle(StringRef Name,
                          IdentifierNamingCheck::NamingStyle Style) {