[ADT] Add `StringRef::rsplit(StringRef Separator)`.

Summary: Add `StringRef::rsplit(StringRef Separator)` to achieve the function of getting the tail substring according to the separator. A typical usage is to get `data` in `std::basic_string::data`.

Reviewers: mehdi_amini, zturner, beanz, xbolva00, vsk

Reviewed By: zturner, xbolva00, vsk

Subscribers: vsk, xbolva00, llvm-commits, MTC

Differential Revision: https://reviews.llvm.org/D47406

llvm-svn: 334283

llvm/include/llvm/ADT/StringRef.h

@@ -725,10 +725,7 @@ namespace llvm {
     /// \returns The split substrings.
     LLVM_NODISCARD
     std::pair<StringRef, StringRef> split(char Separator) const {
-      size_t Idx = find(Separator);
-      if (Idx == npos)
-        return std::make_pair(*this, StringRef());
-      return std::make_pair(slice(0, Idx), slice(Idx+1, npos));
+      return split(StringRef(&Separator, 1));
     }
 
     /// Split into two substrings around the first occurrence of a separator
@@ -749,6 +746,24 @@ namespace llvm {
       return std::make_pair(slice(0, Idx), slice(Idx + Separator.size(), npos));
     }
 
+    /// Split into two substrings around the last occurrence of a separator
+    /// string.
+    ///
+    /// If \p Separator is in the string, then the result is a pair (LHS, RHS)
+    /// such that (*this == LHS + Separator + RHS) is true and RHS is
+    /// minimal. If \p Separator is not in the string, then the result is a
+    /// pair (LHS, RHS) where (*this == LHS) and (RHS == "").
+    ///
+    /// \param Separator - The string to split on.
+    /// \return - The split substrings.
+    LLVM_NODISCARD
+    std::pair<StringRef, StringRef> rsplit(StringRef Separator) const {
+      size_t Idx = rfind(Separator);
+      if (Idx == npos)
+        return std::make_pair(*this, StringRef());
+      return std::make_pair(slice(0, Idx), slice(Idx + Separator.size(), npos));
+    }
+
     /// Split into substrings around the occurrences of a separator string.
     ///
     /// Each substring is stored in \p A. If \p MaxSplit is >= 0, at most
@@ -796,10 +811,7 @@ namespace llvm {
     /// \return - The split substrings.
     LLVM_NODISCARD
     std::pair<StringRef, StringRef> rsplit(char Separator) const {
-      size_t Idx = rfind(Separator);
-      if (Idx == npos)
-        return std::make_pair(*this, StringRef());
-      return std::make_pair(slice(0, Idx), slice(Idx+1, npos));
+      return rsplit(StringRef(&Separator, 1));
     }
 
     /// Return string with consecutive \p Char characters starting from the

llvm/unittests/ADT/StringRefTest.cpp

@@ -181,6 +181,17 @@ TEST(StringRefTest, Split) {
             Str.rsplit('l'));
   EXPECT_EQ(std::make_pair(StringRef("hell"), StringRef("")),
             Str.rsplit('o'));
+
+  EXPECT_EQ(std::make_pair(StringRef("he"), StringRef("o")),
+		    Str.rsplit("ll"));
+  EXPECT_EQ(std::make_pair(StringRef(""), StringRef("ello")),
+		    Str.rsplit("h"));
+  EXPECT_EQ(std::make_pair(StringRef("hell"), StringRef("")),
+	      Str.rsplit("o"));
+  EXPECT_EQ(std::make_pair(StringRef("hello"), StringRef("")),
+		    Str.rsplit("::"));
+  EXPECT_EQ(std::make_pair(StringRef("hel"), StringRef("o")),
+		    Str.rsplit("l"));
 }
 
 TEST(StringRefTest, Split2) {