[PATCH] Verify source files for a module only once during the build

[Dmitri Gribenko]

On Fri, Feb 7, 2014 at 6:31 PM, Argyrios Kyrtzidis <kyrtzidis at apple.com> wrote:
> +def fmodules_skip_verify_if_validated_after : Joined<["-"],
> "fmodules-skip-verify-if-validated-after=">,
>
> Should we use a more general name, like “-fbuild-session-timestamp” or
> something, this seems like it could have other uses in the future.

I like the current name because clang does what the option name says.
If build session timestamp could be used for more features, I'd prefer
to have two options then:

-fbuild-session-timestamp=... -fmodules-validate-once-per-build-session

> +static void updateModuleTimestamp(ModuleFile &MF) {
> +  // Overwrite the timestamp file contents so that file's mtime changes.
> +  std::string TimestampFilename = MF.getTimestampFilename();
> +  std::string ErrorInfo;
> +  llvm::raw_fd_ostream OS(TimestampFilename.c_str(), ErrorInfo);
> +  if (!ErrorInfo.empty())
> +    return;
> +  OS << "Timestamp file\n";
> +}
>
> +    New->InputFilesValidationTimestamp = 0;
> +    if (New->Kind == MK_Module) {
> +      std::string TimestampFilename = New->getTimestampFilename();
> +      llvm::sys::fs::file_status Status;
> +      // A cached stat value would be fine as well.
> +      if (!FileMgr.getNoncachedStatValue(TimestampFilename, Status)) {
> +        llvm::sys::TimeValue MTime = Status.getLastModificationTime();
> +        New->InputFilesValidationTimestamp =
> +            MTime.toEpochTime() * 1000 + MTime.milliseconds();
> +      }
> +    }
> +
>
> I’m concerned that we are depending on being in-sync with the modification
> time given by the file system and the builder that provided the original
> timestamp.

I wanted to avoid the need to do the atomic-rename dance.  What is the
potential for mtime confusion that you see?  We could provide a
function in libclang to get the current timestamp so that clients
don't have to invent their own, potentially incorrect way to get it.

Dmitri

-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/