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

[Samuel Thibault]

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

-- System Information:
Debian Release: bullseye/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable-debug'), (500, 'testing-debug'), (500, 'stable-debug'), (500, 'proposed-updates-debug'), (500, 'proposed-updates'), (500, 'oldstable-proposed-updates-debug'), (500, 'oldstable-proposed-updates'), (500, 'oldoldstable'), (500, 'buildd-unstable'), (500, 'unstable'), (500, 'stable'), (500, 'oldstable'), (1, 'experimental-debug'), (1, 'buildd-experimental'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.3.0 (SMP w/8 CPU cores)
Kernel taint flags: TAINT_OOT_MODULE
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8), LANGUAGE=fr_FR.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

-- 
Samuel
<y> t1 faich
<y> les programmes ils segfaultent jamais quand on veut
 -+- #ens-mim en plein débogage -+-