[PATCH] D27686: Add llvm::StringLiteral

[Zachary Turner via Phabricator via llvm-commits]

zturner created this revision.
zturner added reviewers: malcolm.parsons, mehdi_amini.
zturner added a subscriber: llvm-commits.

As discussed on the mailing list, this allows us to create global tables of StringRefs that don't incur a global constructor.


https://reviews.llvm.org/D27686

Files:
  include/llvm/ADT/StringRef.h
  unittests/ADT/StringRefTest.cpp


Index: unittests/ADT/StringRefTest.cpp
===================================================================
--- unittests/ADT/StringRefTest.cpp
+++ unittests/ADT/StringRefTest.cpp
@@ -1002,4 +1002,10 @@
   EXPECT_EQ("", Taken);
 }
 
+TEST(StringRefTest, StringLiteral) {
+  constexpr StringLiteral Strings[] = {"Foo", "Bar"};
+  EXPECT_STREQ("Foo", Strings[0].data());
+  EXPECT_STREQ("Bar", Strings[1].data());
+}
+
 } // end anonymous namespace
Index: include/llvm/ADT/StringRef.h
===================================================================
--- include/llvm/ADT/StringRef.h
+++ include/llvm/ADT/StringRef.h
@@ -84,11 +84,8 @@
 
     /// Construct a string ref from a pointer and length.
     LLVM_ATTRIBUTE_ALWAYS_INLINE
-    /*implicit*/ StringRef(const char *data, size_t length)
-      : Data(data), Length(length) {
-        assert((data || length == 0) &&
-        "StringRef cannot be built from a NULL argument with non-null length");
-      }
+    /*implicit*/ constexpr StringRef(const char *data, size_t length)
+        : Data(data), Length(length) {}
 
     /// Construct a string ref from an std::string.
     LLVM_ATTRIBUTE_ALWAYS_INLINE
@@ -839,6 +836,20 @@
     /// @}
   };
 
+  /// StringLiteral - A wrapper around a StringLiteral that serves as a proxy
+  /// for constructing global tables of StringRefs with the length computed
+  /// at compile time.  Using this class with a non-literal char array is
+  /// considered undefined behavior.  To prevent this, it is recommended
+  /// that StringLiteral *only* be used in a constexpr context, as such:
+  ///
+  /// constexpr StringLiteral S("test");
+  ///
+  class StringLiteral : public StringRef {
+  public:
+    template <size_t N>
+    constexpr StringLiteral(const char (&Str)[N]) : StringRef(Str, N) {}
+  };
+
   /// @name StringRef Comparison Operators
   /// @{
 


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