[llvm] r202225 - Use StringRef in raw_fd_ostream constructor

[Ben Langmuir]

On Feb 25, 2014, at 9:49 PM, Alp Toker <alp at nuanti.com> wrote:

> On 26/02/2014 03:21, Ben Langmuir wrote:
>> Author: benlangmuir
>> Date: Tue Feb 25 21:21:00 2014
>> New Revision: 202225
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=202225&view=rev
>> Log:
>> Use StringRef in raw_fd_ostream constructor
>> 
>> Modified:
>>     llvm/trunk/include/llvm/Support/raw_ostream.h
>>     llvm/trunk/lib/Support/raw_ostream.cpp
>> 
>> Modified: llvm/trunk/include/llvm/Support/raw_ostream.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/raw_ostream.h?rev=202225&r1=202224&r2=202225&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Support/raw_ostream.h (original)
>> +++ llvm/trunk/include/llvm/Support/raw_ostream.h Tue Feb 25 21:21:00 2014
>> @@ -346,7 +346,7 @@ public:
>>    /// itself to own the file descriptor. In particular, it will close the
>>    /// file descriptor when it is done (this is necessary to detect
>>    /// output errors).
>> -  raw_fd_ostream(const char *Filename, std::string &ErrorInfo,
>> +  raw_fd_ostream(StringRef Filename, std::string &ErrorInfo,
>>                   sys::fs::OpenFlags Flags);
> 
> Filenames are a special case in LLVM that get passed around as an opaque const char* often without ever needing having their length measured (like the clang driver code I'm looking at right now).
> 
> Your change will incur a strlen() upon every ctor call: not a great problem, but also somewhat redundant -- was there a need that triggered this change?

I intend to make FileEntry in Clang own the storage for its file name, which seemed like a good opportunity to change the FileEntry getName to return a StringRef, particularly because it is currently being used/abused to also check if the FileEntry is initialized.  This was one of the pieces that uses that name, so I thought I’d avoid a string copy before passing it in.

What if I switch to raw_fd_ostream(const Twine &Filename, …)?  Then if it is null-terminated we don’t need the strlen call.

Ben

> 
> Alp.
> 
>>      /// raw_fd_ostream ctor - FD is the file descriptor that this writes to.  If
>> 
>> Modified: llvm/trunk/lib/Support/raw_ostream.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/raw_ostream.cpp?rev=202225&r1=202224&r2=202225&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Support/raw_ostream.cpp (original)
>> +++ llvm/trunk/lib/Support/raw_ostream.cpp Tue Feb 25 21:21:00 2014
>> @@ -430,16 +430,15 @@ void format_object_base::home() {
>>  /// occurs, information about the error is put into ErrorInfo, and the
>>  /// stream should be immediately destroyed; the string will be empty
>>  /// if no error occurred.
>> -raw_fd_ostream::raw_fd_ostream(const char *Filename, std::string &ErrorInfo,
>> +raw_fd_ostream::raw_fd_ostream(StringRef Filename, std::string &ErrorInfo,
>>                                 sys::fs::OpenFlags Flags)
>>      : Error(false), UseAtomicWrites(false), pos(0) {
>> -  assert(Filename != 0 && "Filename is null");
>>    ErrorInfo.clear();
>>      // Handle "-" as stdout. Note that when we do this, we consider ourself
>>    // the owner of stdout. This means that we can do things like close the
>>    // file descriptor when we're done and set the "binary" flag globally.
>> -  if (Filename[0] == '-' && Filename[1] == 0) {
>> +  if (Filename == "-") {
>>      FD = STDOUT_FILENO;
>>      // If user requested binary then put stdout into binary mode if
>>      // possible.
>> 
>> 
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