Sanitize the output of llvm-config when building with external LLVM

[ghost]

My LLVM, built with clang:

$ llvm-config --cflags

-I/usr/include -march=native -pipe -O3 -fPIC -Wall -W -Wno-unused-parameter -Wwrite-strings -Wmissing-field-initializers -pedantic -Wno-long-long -Wcovered-switch-default   -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS

Building with gcc:

$ ../configure --llvm-root=/usr --prefix=$HOME/sys && make
<snip>
g++: error: unrecognized command line option ‘-Wcovered-switch-default’
/home/jurily/cucc/src/rust/rust/mk/rustllvm.mk:46: recipe for target 'x86_64-unknown-linux-gnu/rustllvm/RustWrapper.o' failed
make: *** [x86_64-unknown-linux-gnu/rustllvm/RustWrapper.o] Error 1

[tfogal]

I am hitting this error message just trying to build Rust:

llvm[2]: Compiling ConvertUTF.c for Debug+Asserts build
gcc: error: unrecognized command line option ‘-Wcovered-switch-default’
/bin/rm: cannot remove ‘/home/tfogal/dev/rust/x86_64-unknown-linux-gnu/llvm/lib/Support/Debug+Asserts/ConvertUTF.d.tmp’: No such file or directory
make[2]: *** [/home/tfogal/dev/rust/x86_64-unknown-linux-gnu/llvm/lib/Support/Debug+Asserts/ConvertUTF.o] Error 1
make[2]: Leaving directory `/home/tfogal/dev/rust/x86_64-unknown-linux-gnu/llvm/lib/Support'
make[1]: *** [all] Error 1

I configure via:

#!/bin/sh

./configure \
  --disable-docs \
  --disable-optimize-llvm \
  --disable-jemalloc \
  --prefix=${HOME}/sw/ \
  --local-rust-root=${HOME}/sw/ \
  $@

Is there a workaround?

[tamird]

Relevant: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61864

[MagaTailor]

I updated llvm to 3.7.1 on Slackware current to get rid of this issue but suddenly I'm getting the above-mentioned build error using both gcc 5.3.0 and 4.9..

Did the -Wcovered-switch-default flag get there from building llvm with clang? (yes it did)

$ /mnt/usr/bin/llvm-config --cflags

-I/mnt/usr/include -O2 -march=i586 -mtune=i686 -fPIC -Wall -W -Wno-unused-parameter -Wwrite-strings -Wmissing-field-initializers -pedantic -Wno-long-long -Wcovered-switch-default -ffunction-sections -fdata-sections -O3 -DNDEBUG  -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS

[MagaTailor]

It's about compiling just three C++ files so it's a minor mistake in the build scripts.
The correct logic would clear this flag from llvm-config output in case gcc/g++ is being used to build rustc.

[MagaTailor]

@retarded_fag @alexcrichton Someone has just got bitten by this again.

[Mark-Simulacrum]

Okay, to triage this issue a little, I think this is about us using llvm-config's output to generate gcc parameters, which breaks on external LLVM's, since those can get built with different gcc/linker params.

The current situation appears to be unchanged, but cc @brson for confirmation.

[Mark-Simulacrum]

I don't believe this is a bug anymore, closing -- if someone reproduces, let us know and we'll reopen.