[ADT] Add StringRef::{l,r}trim(char) overloads (NFC)

Add support for trimming a single kind of character from a StringRef.
This makes the common case of trimming null bytes much neater. It's also
probably a bit speedier too, since it avoids creating a std::bitset in
find_{first,last}_not_of.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@260925 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/StringRef.h

@@ -539,18 +539,36 @@ namespace llvm {
       return std::make_pair(slice(0, Idx), slice(Idx+1, npos));
     }
 
+    /// Return string with consecutive \p Char characters starting from the
+    /// the left removed.
+    StringRef ltrim(char Char) const {
+      return drop_front(std::min(Length, find_first_not_of(Char)));
+    }
+
     /// Return string with consecutive characters in \p Chars starting from
     /// the left removed.
     StringRef ltrim(StringRef Chars = " \t\n\v\f\r") const {
       return drop_front(std::min(Length, find_first_not_of(Chars)));
     }
 
+    /// Return string with consecutive \p Char characters starting from the
+    /// right removed.
+    StringRef rtrim(char Char) const {
+      return drop_back(Length - std::min(Length, find_last_not_of(Char) + 1));
+    }
+
     /// Return string with consecutive characters in \p Chars starting from
     /// the right removed.
     StringRef rtrim(StringRef Chars = " \t\n\v\f\r") const {
       return drop_back(Length - std::min(Length, find_last_not_of(Chars) + 1));
     }
 
+    /// Return string with consecutive \p Char characters starting from the
+    /// left and right removed.
+    StringRef trim(char Char) const {
+      return ltrim(Char).rtrim(Char);
+    }
+
     /// Return string with consecutive characters in \p Chars starting from
     /// the left and right removed.
     StringRef trim(StringRef Chars = " \t\n\v\f\r") const {

unittests/ADT/StringRefTest.cpp

@@ -301,7 +301,7 @@ TEST(StringRefTest, Trim) {
   EXPECT_EQ(StringRef(""), StringRef(" ").trim());
   EXPECT_EQ(StringRef("\0", 1), StringRef(" \0 ", 3).trim());
   EXPECT_EQ(StringRef("\0\0", 2), StringRef("\0\0", 2).trim());
-  EXPECT_EQ(StringRef("x"), StringRef("\0\0x\0\0", 5).trim(StringRef("\0", 1)));
+  EXPECT_EQ(StringRef("x"), StringRef("\0\0x\0\0", 5).trim('\0'));
 }
 
 TEST(StringRefTest, StartsWith) {