Bug#943920: llvm-toolchain-8: FTBFS since migration of gcc-defaults to gcc-9

[Sylvestre Ledru]

Le 31/10/2019 à 22:51, Samuel Thibault a écrit :
> Source: llvm-toolchain-8
> Version: 1:8.0.1-3
> Severity: serious
> Justification: FTBFS
>
> Hello,
>
> Since the migration of gcc-defaults to gcc-9, llvm-toolchain-8 FTBFS,
> with
>
>
>
> CMake Error at tools/polly/lib/External/CMakeLists.txt:91 (message):
>    No ffs implementation found
>
>
> looking at CMakeError.log, one actually see:
>
>
> Source file was:
>
>    int main() { (void)__builtin_ffs(0); return 0; }
>    
> Performing C SOURCE FILE Test HAVE_DECL__BITSCANFORWARD failed with the following output:
> Change Dir: /build/llvm-toolchain-8-8.0.1/build-llvm/CMakeFiles/CMakeTmp
>
> Run Build Command:"/usr/bin/make" "cmTC_11f2c/fast"
> make[2]: Entering directory '/build/llvm-toolchain-8-8.0.1/build-llvm/CMakeFiles/CMakeTmp'
> /usr/bin/make -f CMakeFiles/cmTC_11f2c.dir/build.make CMakeFiles/cmTC_11f2c.dir/build
> make[3]: Entering directory '/build/llvm-toolchain-8-8.0.1/build-llvm/CMakeFiles/CMakeTmp'
> Building C object CMakeFiles/cmTC_11f2c.dir/src.c.o
> /usr/bin/gcc-9 -D_GNU_SOURCE  -g -O2 -fdebug-prefix-map=/build/llvm-toolchain-8-8.0.1=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-comment -ffunction-sections -fdata-sections -flto=thin -DHAVE_DECL__BITSCANFORWARD   -o CMakeFiles/cmTC_11f2c.dir/src.c.o   -c /build/llvm-toolchain-8-8.0.1/build-llvm/CMakeFiles/CMakeTmp/src.c
> cc1: error: unrecognized argument to '-flto=' option: 'thin'
>
>
> i.e. llvm passed -flto=thin to gcc-9, which does not understand it.
> gcc-8 used to understand it, but not gcc-9 any more. I had to comment in
> debian/rules CMAKE_EXTRA += -DLLVM_ENABLE_LTO="Thin" to get it built.
>
> Samuel

Indeed, this is why I am forcing the build of -9 with gcc-8 for now :)

See https://bugs.llvm.org/show_bug.cgi?id=43193 for more info!

S