why empty output from gprof on gmon.out produced by Debug+Profile+Asserts/bin/clang?

Compiling a moderately complex template c++ program with the
clang in subject line produced a huge gmon.out:

-rw-r--r-- 1 evansl evansl 18016375 Oct 7 20:28 gmon.out

However, running gprof on that:

~/prog_dev/boost-svn/ro/boost_1_49_0/sandbox/rw/variadic_templates/sandbox/slim/test
$ gprof
/home/evansl/download/llvm/svn/build/Debug+Profile+Asserts/bin/clang
gmon.out > clangxx_dpa.gprof.txt&
[gprof] 27132

took about 1.5 hrs and produced an empty clangxx_dpa.gprof.txt.

What might be going wrong? I did try g++ -pg on a simple hello world
program and gprof on that gmon.out did produce some output.
Has anyone else tried using gprof to analyze where clang is
spending its time?

What's the best way to get profile information about what's
consuming most of the template processing time in clang?

TIA.

-regards,
Larry

Tried the gprof without redirecting to a *.txt file, and now (after
about 1.5 hrs), a huge output is coming out.

I'm not sure why :frowning:

-regards,
Larry