pdp11: 'src' may be used uninitialized in this function

[Jan-Benedict Glaw]

Hi Paul,

using a recent GCC when building GCC results in a possibly
uninitialized access:

$ .../gcc/configure --target=pdp11-aout --enable-werror-always --enable-languages=all --disable-gcov --disable-shared --disable-threads --without-headers
[...]
$ make all-gcc
[...]
[all 2021-09-04 17:21:14] /usr/lib/gcc-snapshot/bin/g++  -fno-PIE -c   -g -O2 -DIN_GCC  -DCROSS_DIRECTORY_STRUCTURE   -fno-exceptions -fno-rtti -fasynchronous-unwind-tables -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wno-error=format-diag -Wmissing-format-attribute -Woverloaded-virtual -pedantic -Wno-long-long -Wno-variadic-macros -Wno-overlength-strings -Werror -fno-common  -DHAVE_CONFIG_H -I. -I. -I../../gcc/gcc -I../../gcc/gcc/. -I../../gcc/gcc/../include -I../../gcc/gcc/../libcpp/include -I../../gcc/gcc/../libcody  -I../../gcc/gcc/../libdecnumber -I../../gcc/gcc/../libdecnumber/dpd -I../libdecnumber -I../../gcc/gcc/../libbacktrace   -o xcoffout.o -MT xcoffout.o -MMD -MP -MF ./.deps/xcoffout.TPo ../../gcc/gcc/xcoffout.c
[all 2021-09-04 17:21:16] /usr/lib/gcc-snapshot/bin/g++  -fno-PIE -c   -g -O2 -DIN_GCC  -DCROSS_DIRECTORY_STRUCTURE   -fno-exceptions -fno-rtti -fasynchronous-unwind-tables -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wno-error=format-diag -Wmissing-format-attribute -Woverloaded-virtual -pedantic -Wno-long-long -Wno-variadic-macros -Wno-overlength-strings -Werror -fno-common  -DHAVE_CONFIG_H -I. -I. -I../../gcc/gcc -I../../gcc/gcc/. -I../../gcc/gcc/../include -I../../gcc/gcc/../libcpp/include -I../../gcc/gcc/../libcody  -I../../gcc/gcc/../libdecnumber -I../../gcc/gcc/../libdecnumber/dpd -I../libdecnumber -I../../gcc/gcc/../libbacktrace   -o pdp11.o -MT pdp11.o -MMD -MP -MF ./.deps/pdp11.TPo ../../gcc/gcc/config/pdp11/pdp11.c
[all 2021-09-04 17:21:19] ../../gcc/gcc/config/pdp11/pdp11.c: In function 'bool pdp11_rtx_costs(rtx, machine_mode, int, int, int*, bool)':
[all 2021-09-04 17:21:19] ../../gcc/gcc/config/pdp11/pdp11.c:1113:39: error: 'src' may be used uninitialized in this function [-Werror=maybe-uninitialized]
[all 2021-09-04 17:21:19]  1113 |             *total += pdp11_addr_cost (src, mode, ADDR_SPACE_GENERIC, speed);
[all 2021-09-04 17:21:19]       |                       ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[all 2021-09-04 17:21:20] cc1plus: all warnings being treated as errors
[all 2021-09-04 17:21:20] make[1]: *** [Makefile:2421: pdp11.o] Error 1
[all 2021-09-04 17:21:20] make[1]: Leaving directory '/var/lib/laminar/run/gcc-pdp11-aout/11/toolchain-build/gcc'
[all 2021-09-04 17:21:20] make: *** [Makefile:4422: all-gcc] Error 2

The warning seems legit, though hardly reachable in reality. Maybe fix
it for sure, though?

Thanks,
  Jan-Benedict

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