[PATCH] D26568: [ADT] Delete Twine constructors which accept StringRef rvalues (NFC)

[Vedant Kumar via llvm-commits]

vsk created this revision.
vsk added reviewers: aprantl, dblaikie.
vsk added a subscriber: llvm-commits.

Twine stores a *pointer to a StringRef*, not a StringRef. Taking the address of a StringRef rvalue could easily give us a dangling pointer.

Adrian ran into this issue in the wild (see r286640). Deleting these constructors was his idea.

llvm/clang are teeming with Twine abuse, so landing this patch right now would break all of our builds. If this patch looks OK, I can start weeding out the issues.


https://reviews.llvm.org/D26568

Files:
  include/llvm/ADT/Twine.h


Index: include/llvm/ADT/Twine.h
===================================================================
--- include/llvm/ADT/Twine.h
+++ include/llvm/ADT/Twine.h
@@ -370,6 +370,13 @@
       assert(isValid() && "Invalid twine!");
     }
 
+    /// Do not construct from StringRef rvalues. Twine stores a *pointer to a
+    /// StringRef*, not a StringRef. Taking the address of a StringRef rvalue
+    /// could easily give us a dangling pointer.
+    /*implicit*/ Twine(StringRef &&) = delete;
+    /*implicit*/ Twine(const char *, StringRef &&) = delete;
+    /*implicit*/ Twine(StringRef &&, const char *) = delete;
+
     /// Create a 'null' string, which is an empty string that always
     /// concatenates to form another empty string.
     static Twine createNull() {
@@ -522,6 +529,8 @@
     return Twine(LHS, RHS);
   }
 
+  inline Twine operator+(const char *, StringRef &&) = delete;
+
   /// Additional overload to guarantee simplified codegen; this is equivalent to
   /// concat().
 
@@ -529,6 +538,8 @@
     return Twine(LHS, RHS);
   }
 
+  inline Twine operator+(StringRef &&, const char *) = delete;
+
   inline raw_ostream &operator<<(raw_ostream &OS, const Twine &RHS) {
     RHS.print(OS);
     return OS;


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