[clang-tidy][NFC] Tweak GlobList to iterate backwards

By iterating backwards over the globs we can exit the loop as soon as we find a match.

While we're here:
 - Regex doesn't need to be mutable.
 - We can reserve the amount of Globs needed ahead of time.
 - Using a SmallVector with size 0 is slightly more space efficient than a std::vector.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D91033

clang-tools-extra/clang-tidy/GlobList.cpp

@@ -34,7 +34,7 @@ static llvm::Regex ConsumeGlob(StringRef &GlobList) {
   for (char C : Glob) {
     if (C == '*')
       RegexText.push_back('.');
-    else if (MetaChars.find(C) != StringRef::npos)
+    else if (MetaChars.contains(C))
       RegexText.push_back('\\');
     RegexText.push_back(C);
   }
@@ -43,6 +43,7 @@ static llvm::Regex ConsumeGlob(StringRef &GlobList) {
 }
 
 GlobList::GlobList(StringRef Globs) {
+  Items.reserve(Globs.count(',') + 1);
   do {
     GlobListItem Item;
     Item.IsPositive = !ConsumeNegativeIndicator(Globs);
@@ -52,10 +53,11 @@ GlobList::GlobList(StringRef Globs) {
 }
 
 bool GlobList::contains(StringRef S) {
-  bool Contains = false;
-  for (const GlobListItem &Item : Items) {
+  // Iterating the container backwards as the last match determins if S is in
+  // the list.
+  for (const GlobListItem &Item : llvm::reverse(Items)) {
     if (Item.Regex.match(S))
-      Contains = Item.IsPositive;
+      return Item.IsPositive;
   }
-  return Contains;
+  return false;
 }

clang-tools-extra/clang-tidy/GlobList.h

@@ -10,9 +10,9 @@
 #define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GLOBLIST_H
 
 #include "clang/Basic/LLVM.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Regex.h"
-#include <vector>
 
 namespace clang {
 namespace tidy {
@@ -39,9 +39,9 @@ private:
 
   struct GlobListItem {
     bool IsPositive;
-    mutable llvm::Regex Regex;
+    llvm::Regex Regex;
   };
-  std::vector<GlobListItem> Items;
+  SmallVector<GlobListItem, 0> Items;
 };
 
 } // end namespace tidy