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Building a patched GHC 7.8 for hermit-syb:

First, you need to update happy and alex to the very latest versions so they generate correct primops.

cabal update
cabal install alex
cabal install happy

Then, build a modified 7.8:

# If on windows, uncomment the following line:
# git config --global core.autocrlf false
# NB: on a mac `curl -O` instead of `wget`
git clone -b ghc-7.8 git:// ghc-7.8
cd ghc-7.8
./sync-all get -b ghc-7.8
cd libraries/base
patch -p1 < path/to/hermit-syb/base.patch
cd ../ghc-prim
patch -p1 < path/to/hermit-syb/ghc-prim.patch
cd ../..
cp mk/ mk/

Now edit mk/ and uncomment: BuildFlavour = perf

Now build ghc with the following three commands (and grab drink of your choice):

perl boot

See: if you have problems here.

Once done, symlink the stage2 compiler.

cd inplace/bin
ln -s ghc-stage2 ghc

add the result of pwd to the beginning of your PATH. With the symlink, should allow you to use your existing cabal with your newly compiled GHC HEAD try: which ghc and ghc -V to make sure the right one is being used

Now to build HERMIT itself:

cabal update
# kure
cabal install kure
# syb
git clone
cd syb
cabal install -p
cd ..
# haskell-src
git clone git://
cd haskell-src
patch -p1 < path/to/hermit-syb/haskell-src.patch
cabal install -p
cd ..
# hermit
git clone
cd hermit
cabal install
cd ..

Once that is done:

cd hermit-syb
cabal install
cd ..

hermit Sum.hs -opt=HERMIT.Optimization.SYB +Main mapInt
- or -
hermit Sum.hs -opt=HERMIT.Optimization.SYB +Main mapIntM
- or -
hermit Sum.hs -opt=HERMIT.Optimization.SYB +Main mapInt mapIntM

Note about submodules

A version of HERMIT that works with this plugin is pegged as a submodule, in case the most recent HERMIT does not work. When you first clone this repository, you need to:

git submodule init git submodule update

to pull down the contents of the submodules.

Whenever you pull new changes that include new submodule hashes, you must:

git submodule update

More information on working with submodules:


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