To use the GHC profiler:

first, add -auto-all to ghc-options in pandoc.cabal.  then

make clean
make templates
runhaskell Setup.hs configure --enable-library-profiling --enable-executable-profiling
runhaskell Setup.hs build
dist/build/pandoc/pandoc +RTS -p -RTS [file]...
less pandoc.prof