Store OptTable::Info::Name as a StringRef

This avoids implicit conversion to StringRef at several points, which in
turns avoid redundant calls to strlen.

As a side effect, this greatly simplifies the implementation of
StrCmpOptionNameIgnoreCase.

It also eventually gives a consistent, humble speedup in compilation
time.

https://llvm-compile-time-tracker.com/compare.php?from=5f5b942823474e98e43a27d515a87ce140396c53&to=60e13b778119fc32d50dc38ff1a564a87146e9c6&stat=instructions:u

Differential Revision: https://reviews.llvm.org/D139274

Author: serge-sans-paille

clang/lib/Driver/ToolChains/Gnu.cpp

@@ -331,8 +331,8 @@ static bool getStaticPIE(const ArgList &Args, const ToolChain &TC) {
   if (HasStaticPIE && Args.hasArg(options::OPT_nopie)) {
     const Driver &D = TC.getDriver();
     const llvm::opt::OptTable &Opts = D.getOpts();
-    const char *StaticPIEName = Opts.getOptionName(options::OPT_static_pie);
-    const char *NoPIEName = Opts.getOptionName(options::OPT_nopie);
+    StringRef StaticPIEName = Opts.getOptionName(options::OPT_static_pie);
+    StringRef NoPIEName = Opts.getOptionName(options::OPT_nopie);
     D.Diag(diag::err_drv_cannot_mix_options) << StaticPIEName << NoPIEName;
   }
   return HasStaticPIE;

llvm/include/llvm/Option/OptTable.h

@@ -44,7 +44,7 @@ class OptTable {
     /// A null terminated array of prefix strings to apply to name while
     /// matching.
     const char *const *Prefixes;
-    const char *Name;
+    StringRef Name;
     const char *HelpText;
     const char *MetaVar;
     unsigned ID;
@@ -102,9 +102,7 @@ class OptTable {
   const Option getOption(OptSpecifier Opt) const;
 
   /// Lookup the name of the given option.
-  const char *getOptionName(OptSpecifier id) const {
-    return getInfo(id).Name;
-  }
+  StringRef getOptionName(OptSpecifier id) const { return getInfo(id).Name; }
 
   /// Get the kind of the given option.
   unsigned getOptionKind(OptSpecifier id) const {
@@ -184,7 +182,7 @@ class OptTable {
   ///  takes
   ///
   /// \return true in success, and false in fail.
-  bool addValues(const char *Option, const char *Values);
+  bool addValues(StringRef Option, const char *Values);
 
   /// Parse a single argument; returning the new argument and
   /// updating Index.

llvm/lib/Option/OptTable.cpp

@@ -36,31 +36,23 @@ namespace opt {
 // Ordering on Info. The ordering is *almost* case-insensitive lexicographic,
 // with an exception. '\0' comes at the end of the alphabet instead of the
 // beginning (thus options precede any other options which prefix them).
-static int StrCmpOptionNameIgnoreCase(const char *A, const char *B) {
-  const char *X = A, *Y = B;
-  char a = tolower(*A), b = tolower(*B);
-  while (a == b) {
-    if (a == '\0')
-      return 0;
-
-    a = tolower(*++X);
-    b = tolower(*++Y);
-  }
+static int StrCmpOptionNameIgnoreCase(StringRef A, StringRef B) {
+  size_t MinSize = std::min(A.size(), B.size());
+  if (int Res = A.substr(0, MinSize).compare_insensitive(B.substr(0, MinSize)))
+    return Res;
 
-  if (a == '\0') // A is a prefix of B.
-    return 1;
-  if (b == '\0') // B is a prefix of A.
-    return -1;
+  if (A.size() == B.size())
+    return 0;
 
-  // Otherwise lexicographic.
-  return (a < b) ? -1 : 1;
+  return (A.size() == MinSize) ? 1 /* A is a prefix of B. */
+                               : -1 /* B is a prefix of A */;
 }
 
 #ifndef NDEBUG
-static int StrCmpOptionName(const char *A, const char *B) {
+static int StrCmpOptionName(StringRef A, StringRef B) {
   if (int N = StrCmpOptionNameIgnoreCase(A, B))
     return N;
-  return strcmp(A, B);
+  return A.compare(B);
 }
 
 static inline bool operator<(const OptTable::Info &A, const OptTable::Info &B) {
@@ -86,7 +78,7 @@ static inline bool operator<(const OptTable::Info &A, const OptTable::Info &B) {
 #endif
 
 // Support lower_bound between info and an option name.
-static inline bool operator<(const OptTable::Info &I, const char *Name) {
+static inline bool operator<(const OptTable::Info &I, StringRef Name) {
   return StrCmpOptionNameIgnoreCase(I.Name, Name) < 0;
 }
 
@@ -321,7 +313,7 @@ unsigned OptTable::findNearest(StringRef Option, std::string &NearestString,
   return BestDistance;
 }
 
-bool OptTable::addValues(const char *Option, const char *Values) {
+bool OptTable::addValues(StringRef Option, const char *Values) {
   for (size_t I = FirstSearchableIndex, E = OptionInfos.size(); I < E; I++) {
     Info &In = OptionInfos[I];
     if (optionMatches(In, Option)) {
@@ -347,8 +339,8 @@ std::unique_ptr<Arg> OptTable::parseOneArgGrouped(InputArgList &Args,
 
   const Info *End = OptionInfos.data() + OptionInfos.size();
   StringRef Name = Str.ltrim(PrefixChars);
-  const Info *Start = std::lower_bound(
-      OptionInfos.data() + FirstSearchableIndex, End, Name.data());
+  const Info *Start =
+      std::lower_bound(OptionInfos.data() + FirstSearchableIndex, End, Name);
   const Info *Fallback = nullptr;
   unsigned Prev = Index;
 
@@ -415,7 +407,7 @@ std::unique_ptr<Arg> OptTable::ParseOneArg(const ArgList &Args, unsigned &Index,
   StringRef Name = StringRef(Str).ltrim(PrefixChars);
 
   // Search for the first next option which could be a prefix.
-  Start = std::lower_bound(Start, End, Name.data());
+  Start = std::lower_bound(Start, End, Name);
 
   // Options are stored in sorted order, with '\0' at the end of the
   // alphabet. Since the only options which can accept a string must

llvm/unittests/Option/OptionMarshallingTest.cpp

@@ -6,10 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/StringRef.h"
 #include "gtest/gtest.h"
 
 struct OptionWithMarshallingInfo {
-  const char *Name;
+  llvm::StringRef Name;
   const char *KeyPath;
   const char *ImpliedCheck;
   const char *ImpliedValue;
@@ -27,10 +28,10 @@ static const OptionWithMarshallingInfo MarshallingTable[] = {
 };
 
 TEST(OptionMarshalling, EmittedOrderSameAsDefinitionOrder) {
-  ASSERT_STREQ(MarshallingTable[0].Name, "marshalled-flag-d");
-  ASSERT_STREQ(MarshallingTable[1].Name, "marshalled-flag-c");
-  ASSERT_STREQ(MarshallingTable[2].Name, "marshalled-flag-b");
-  ASSERT_STREQ(MarshallingTable[3].Name, "marshalled-flag-a");
+  ASSERT_STREQ(MarshallingTable[0].Name.data(), "marshalled-flag-d");
+  ASSERT_STREQ(MarshallingTable[1].Name.data(), "marshalled-flag-c");
+  ASSERT_STREQ(MarshallingTable[2].Name.data(), "marshalled-flag-b");
+  ASSERT_STREQ(MarshallingTable[3].Name.data(), "marshalled-flag-a");
 }
 
 TEST(OptionMarshalling, EmittedSpecifiedKeyPath) {

llvm/utils/TableGen/OptParserEmitter.cpp

@@ -54,9 +54,9 @@ static std::string getOptionSpelling(const Record &R) {
 
 static void emitNameUsingSpelling(raw_ostream &OS, const Record &R) {
   size_t PrefixLength;
-  OS << "&";
+  OS << "llvm::StringRef(";
   write_cstring(OS, StringRef(getOptionSpelling(R, PrefixLength)));
-  OS << "[" << PrefixLength << "]";
+  OS << ").substr(" << PrefixLength << ")";
 }
 
 class MarshallingInfo {