git diff of clang-omp

I know this is somewhat off-topic for this mailing list but it does relate to the use of openmp and the clang-omp github doesn’t have an associated mailing list. I have been trying to generate a diff of what changes residing in clang-omp (based on 3.4) still have to be merged into clang svn. To do this, I started with…

% git clone -b release_34
% cd clang
% git checkout a335ba031b18e2736120b5b82bfee08c50ec522c

to checkout the release_34 branch and roll it back to the 3.4 release (which is what clang-omp is supposed to be based on).
I then though I should be able to generate a git diff with…

% git remote add -f b

% git diff master remotes/b/master

but this seems to be ignoring the roll-back of the the clang release_34 branch. Do I need to do something for the last two commands in order to ensure that the git diff is against the release_34 branch at commit a335ba031b18e2736120b5b82bfee08c50ec522c?
ps My goal was to be able to compare the commits already made into clang svn at with the generated diff see how far away we are from a complete merge.