[PATCH] Allow for the use of StringRef command line options instead of cl::opt<std::string>

[Puyan Lotfi]

It wouldn’t be the common case. But it would reduce string copies resulting from parser::parse().

On Aug 15, 2013, at 5:01 PM, Reid Kleckner <rnk at google.com> wrote:

> If CommandLine owns the strings, then why not just use cl::opt<std::string>?
> 
> 
> On Thu, Aug 15, 2013 at 4:56 PM, Puyan Lotfi <plotfi at apple.com> wrote:
> 
> This sounds like a workable compromise.
> To avoid leaking how about a CommandLine.cpp handled string pool that allocates copies on demand (specified maybe by an optional flag to ParseCommandLineOptions/ParseEnvironmentOptions) but also has the option of flushing/deallocating the pool?
> 
> -Puyan
> 
> On Aug 15, 2013, at 1:47 PM, Chris Lattner <clattner at apple.com> wrote:
> 
> >
> > On Aug 14, 2013, at 4:06 PM, Puyan Lotfi <plotfi at apple.com> wrote:
> >
> >> Oh wow. I see that.
> >>
> >> I am not completely sure how the char* arrays would get handled this way.
> >> I did not make any clang modifications in this patch (although since clang is using the cl library it is affected) but I noticed that the use of cl:: in the llvm source tree made use of global cl::opt variables that specify the opt type.
> >> I don’t see that in the files handling the -mllvm options; I’ll have to look at the CommandLine.cpp code a little more closely to be sure in this case that the char*’s aren’t being implicitly put into StringRefs that might have their data pointers deallocated after cl::ParseCommandLineOptions() is called.
> >
> > After thinking about it for a bit, how about we go with this approach:
> >
> > 1. Document ParseCommandLineOptions/ParseEnvironmentOptions to only work with strings that live forever in CommandLine.h
> > 2. Change clang to leak (or store globally) the strings that are affected.
> >
> > I don't think it is worth designing a context system or anything like that to handle this case.
> >
> > -Chris
> 
> 
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