Build fails with LTO

[eli-schwartz]

I tried to build with the following *FLAGS to optimize the build: -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing

Note the -Werror=* flags are used to help detect cases where the compiler tries to optimize by assuming UB cannot exist in the source code -- if it does exist, ordinarily the code would be miscompiled, and this says to make the miscompilation a fatal error.

I got this error:

make[1]: Entering directory '/var/tmp/portage/media-plugins/x42-plugins-20220714/work/x42-plugins-20220714/meters.lv2'
x86_64-pc-linux-gnu-g++  -I. -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat -Werror=format-security -Werror=implicit-function-declaration -Werror=implicit-int -Werror=int-conversion -Werror=incompatible-pointer-types -g -msse -msse2 -mfpmath=sse -fomit-frame-pointer -O3 -fno-finite-math-only -DNDEBUG -DXTERNAL_UI -DHAVE_LV2_1_8 -fPIC -fvisibility=hidden `pkg-config --cflags lv2` -DVERSION="\"0.9.22\"" -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat -Werror=format-security -DVERSION="\"0.9.22\"" `pkg-config --cflags cairo pangocairo pango` -I../robtk/ -DDISPLAY_INTERFACE -I.  `pkg-config --cflags jack lv2 pango pangocairo ` `pkg-config  --cflags liblo` -DHAVE_LIBLO -pthread -DDEFAULT_NOT_ONTOP \
  -DXTERNAL_UI -DHAVE_IDLE_IFACE \
  -DJACK_DESCRIPT="\"lv2ttl/plugins.h\"" \
  -DAPPNAME="\"meter\"" \
  -o x42/x42-meter-collection \
  ../robtk/jackwrap.c ../robtk/pugl/pugl_x11.c   \
  -DX42_MULTIPLUGIN src/meters.cc jmeters/vumeterdsp.cc jmeters/iec1ppmdsp.cc jmeters/iec2ppmdsp.cc jmeters/stcorrdsp.cc jmeters/msppmdsp.cc ebumeter/ebu_r128_proc.cc jmeters/truepeakdsp.cc jmeters/kmeterdsp.cc zita-resampler/resampler.cc zita-resampler/resampler-table.cc x42/x42-ebur128.o x42/x42-phase-correlation.o x42/x42-dr14.o x42/x42-k20rms.o x42/x42-goniometer.o x42/x42-phasewheel.o x42/x42-histogram.o x42/x42-bitmeter.o x42/x42-surmeter.o x42/x42-spectrum30.o x42/x42-stereoscope.o x42/x42-truepeakrms.o `pkg-config --cflags --libs fftw3f` -lm \
  -Wl,-O1 -Wl,--as-needed -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Wl,--defsym=__gentoo_check_ldflags__=0 -lm -lX11 `pkg-config --libs  cairo pangocairo pango glu gl`  `pkg-config  --libs jack` `pkg-config  --libs liblo`
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
../robtk/jackwrap.c: In function ‘int main(int, char**)’:
../robtk/jackwrap.c:1671:30: warning: ignoring return value of ‘int system(const char*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
 1671 |                 (void)system ("xmessage -button ok -center \"Cannot connect to JACK.\nPlease start the JACK Server first.\" &");
      |                       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-int’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=int-conversion’ is not valid for C++
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=incompatible-pointer-types’ is not valid for C++
src/goniometer.h:168:3: error: type ‘struct LV2gm’ violates the C++ One Definition Rule [-Werror=odr]
  168 | } LV2gm;
      |   ^
./gui/../src/goniometer.h:168:3: note: a different type is defined in another translation unit
  168 | } LV2gm;
      |   ^
src/goniometer.h:151:20: note: the first difference of corresponding definitions is field ‘cor’
  151 |         Stcorrdsp *cor;
      |                    ^
./gui/../src/goniometer.h:151:20: note: a field of same name but different type is defined in another translation unit
  151 |         Stcorrdsp *cor;
      |                    ^
src/../jmeters/stcorrdsp.h:27:7: note: type ‘struct Stcorrdsp’ should match type ‘Stcorrdsp’
   27 | class Stcorrdsp
      |       ^
src/meters.cc:68:6: error: type ‘MtrType’ violates the C++ One Definition Rule [-Werror=odr]
   68 | enum MtrType {
      |      ^
./gui/needle.c:34:6: note: an enum with different value name is defined in another translation unit
   34 | enum MtrType {
      |      ^
src/meters.cc:69:9: note: name ‘MT_NONE’ differs from name ‘MT_BBC’ defined in another translation unit
   69 |         MT_NONE = 0,
      |         ^
./gui/needle.c:35:9: note: mismatching definition
   35 |         MT_BBC = 1,
      |         ^
lto1: some warnings being treated as errors
lto-wrapper: fatal error: x86_64-pc-linux-gnu-g++ returned 1 exit status
compilation terminated.
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: error: lto-wrapper failed
collect2: error: ld returned 1 exit status
make[1]: *** [../robtk/robtk.mk:125: x42/x42-meter-collection] Error 1
make[1]: Leaving directory '/var/tmp/portage/media-plugins/x42-plugins-20220714/work/x42-plugins-20220714/meters.lv2'
make: *** [Makefile:40: meters.lv2] Error 2
 * ERROR: media-plugins/x42-plugins-20220714::gentoo failed (compile phase):

Note this is built via the x42-plugins repo, but I checked this repo and the code pattern is still there.

Originally reported downstream: https://bugs.gentoo.org/860402
Full build log: build.log