Some formulae are able to detect the features of the runtime CPU, and
execute code accordingly. This typically entails 1) the detection of
features of the build-time CPU in order to determine the targets that
the compiler can generate code for, and 2) generating code for the
targets that the compiler can support.
Our filtering of optimization flags can cause misdetection of compiler
features, leading to failed builds [1], and miscompilation even when the
build does not fail [2].
Let's try to fix this by allowing formulae to declare
`ENV.runtime_cpu_detection` which skips the filtering of `-march` and
related flags.
I've also skipped the filtering of the optimisation
level, since it seems to me that if upstream maintainers have gone to
the lengths of writing code that detects runtime hardware, they probably
also know better about appropriate `-O` flags to use.
This is a partial list of formulae that should make use of this feature:
1. apache-arrow
2. fftw
3. gromacs
4. open-mpi
5. openblas
Partially resolvesHomebrew/homebrew-core#76537.
[1] open-mpi/ompi#8306 and linked issues/PRs
[2] Homebrew/homebrew-core#76537
The shim currently does not handle `--sysroot=` and `-isysroot=` flags
correctly. For example, the LLVM build passes `--sysroot=.`, and this is
incorrectly parsed by the shim.
Combined with https://github.com/Homebrew/homebrew-test-bot/pull/247
this will test Homebrew's use of frozen strings in CI. After this we
will then enable it for Homebrew developers and eventually all Homebrew
users.
The regular expression check for the -mmacosx-version-min value only
looked at a single digit in the minor version number, so it did not
compare correctly if the option was setting the minimum version
to (say) 10.11.
Clang has fully implemented OpenMP support as of LLVM 3.7, so if OpenMP
is required by a formula gcc is no longer the only choice of compiler.
Clang should be preferred over gcc because using gcc meant linking
against libstdc++, which is ABI incompatible with libc++. This may be
unnoticeable for some users, but it causes other builds to fail, e.g.
pstoedit when imagemagick was built with OpenMP. pstoedit is required
for the octave formula, so for some users this could be a significant
problem.
`-Wl,-z,defs` should be pruned out entirely since `-z defs` is not
understood by macOS's `ld`, and the analogue `-undefined error` is
already the default.
Not quite a mass replacement as I've used OS X and Mac OS X where
describing specific older versions and added compatibility methods
for things in the DSL.
/usr/local/lib is removed from the default linker search path when
SDKROOT is defined or sysroot is specified.
Homebrew sometimes sets SDKROOT without setting a sysroot as of 45e138f.
