Use linear search instead of std::lower_bound

Author: kparzysz

llvm/lib/Frontend/Directive/Spelling.cpp

@@ -8,24 +8,30 @@
 
 #include "llvm/Frontend/Directive/Spelling.h"
 
-#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/MathExtras.h"
 
 #include <cassert>
 
+static bool Contains(llvm::directive::VersionRange V, int P) {
+  return V.Min <= P && P <= V.Max;
+}
+
 llvm::StringRef llvm::directive::FindName(
     llvm::iterator_range<const llvm::directive::Spelling *> Range,
     unsigned Version) {
   assert(llvm::isInt<8 * sizeof(int)>(Version) && "Version value out of range");
 
   int V = Version;
-  Spelling Tmp{StringRef(), {V, V}};
-  auto F =
-      llvm::lower_bound(Range, Tmp, [](const Spelling &A, const Spelling &B) {
-        return A.Versions < B.Versions;
-      });
-  if (F != Range.end())
-    return F->Name;
+  // Do a linear search to find the first Spelling that contains Version.
+  // The condition "contains(S, Version)" does not partition the list of
+  // spellings, so std::[lower|upper]_bound cannot be used.
+  // In practice the list of spellings is expected to be very short, so
+  // linear search seems appropriate. In general, an interval tree may be
+  // a better choice, but in this case it may be an overkill.
+  for (auto &S : Range) {
+    if (Contains(S.Versions, V))
+      return S.Name;
+  }
   return StringRef();
 }