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Make it clearer how the user can control compiler optimization #530

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Merged
merged 7 commits into from
Sep 21, 2021
Merged

Make it clearer how the user can control compiler optimization #530

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5a9c6f6
Make it clearer how the user can control compiler optimization
gareth-nx Sep 19, 2021
6da1672
fix suggested by awvwgk
gareth-nx Sep 19, 2021
6ec8d6b
remove -fPIC from compiler flags
gareth-nx Sep 20, 2021
cbc8dd6
Mention deletion of the build folder as a strategy for recompiling
gareth-nx Sep 20, 2021
58c9b37
Enable Makefile.manual to use environmental variables for FC, FFLAGS,…
gareth-nx Sep 20, 2021
8178a1c
Remove -flto to make the example almost compiler independent
gareth-nx Sep 20, 2021
dba123d
Quotes for stdlib
gareth-nx Sep 20, 2021
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7 changes: 5 additions & 2 deletions README.md
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Expand Up @@ -125,7 +125,7 @@ cmake -B build
You can pass additional options to CMake to customize the build.
Important options are

- `-G Ninja` to use the Ninja backend instead of the default Make backend. Other build backends are available with a similar syntax.
- `-G Ninja` to use the Ninja backend instead of the default Make backend. This makes it easy to specify compiler flags for the build. Other build backends are available with a similar syntax.
- `-DCMAKE_INSTALL_PREFIX` is used to provide the install location for the library. If not provided the defaults will depend on your operating system, [see here](https://cmake.org/cmake/help/latest/variable/CMAKE_INSTALL_PREFIX.html).
- `-DCMAKE_MAXIMUM_RANK` the maximum array rank procedures should be generated for.
The default value is chosen as 4.
Expand All @@ -134,9 +134,10 @@ Important options are
Compiling with maximum rank 15 can be resource intensive and requires at least 16 GB of memory to allow parallel compilation or 4 GB memory for sequential compilation.
- `-DBUILD_SHARED_LIBS` set to `on` in case you want link your application dynamically against the standard library (default: `off`).

For example, to configure a build using the Ninja backend and generating procedures up to rank 7, which is installed to your home directory use
For example, to configure a build using the Ninja backend while specifying compiler flags `FFLAGS`, generating procedures up to rank 7, and installing to your home directory, use

```sh
export FFLAGS="-O3 -flto -fPIC"
cmake -B build -G Ninja -DCMAKE_MAXIMUM_RANK:String=7 -DCMAKE_INSTALL_PREFIX=$HOME/.local
```

Expand Down Expand Up @@ -177,6 +178,8 @@ You can limit the maximum rank by setting ``-DMAXRANK=<num>`` in the ``FYPPFLAGS
make -f Makefile.manual FYPPFLAGS=-DMAXRANK=4
```

You can edit the compiler and its optimization flags by specifying the `FC` and `FFLAGS` variables in Makefile.manual. The default `FFLAGS` does not include any optimization, and you may want to add `-O3 -flto` to its definition.

### Build with [fortran-lang/fpm](https://github.com/fortran-lang/fpm)

Fortran Package Manager (fpm) is a package manager and build system for Fortran.
Expand Down