Linaro GCC 4.5 switch optimization breaks profiled bootstrap

This bug was split off LP #759409 to track one of the failures discussed there:

Michael Hope wrote on 2011-04-13:

Running a profiled bootstrap of gcc-linaro-4.5+bzr99492 on i686 fails in a couple of places:

http://ex.seabright.co.nz/build/gcc-linaro-4.5+bzr99492%5Eprofiled/logs/i686-lucid-cbuild109-scorpius-profiled/gcc-build.txt
  ../../../gcc-linaro-4.5/gcc/c-opts.c -o c-opts.o
../../../gcc-linaro-4.5/gcc/c-opts.c: In function 'c_common_handle_option':
../../../gcc-linaro-4.5/gcc/c-opts.c:1673:5: internal compiler error: Floating point exception

../../../gcc-linaro-4.5/gcc/config/i386/predicates.md: In function 'fcmov_comparison_operator':
../../../gcc-linaro-4.5/gcc/config/i386/predicates.md:975:3: internal compiler error: Floating point exception

../../../gcc-linaro-4.5/gcc/gcse.c: In function 'oprs_not_set_p':
../../../gcc-linaro-4.5/gcc/gcse.c:1933:3: internal compiler error: Floating point exception

../../../gcc-linaro-4.5/gcc/plugin.c: In function 'invoke_plugin_callbacks':
../../../gcc-linaro-4.5/gcc/plugin.c:476:3: internal compiler error: Floating point exception

../../../gcc-linaro-4.5/gcc/reload1.c: In function 'choose_reload_regs':
../../../gcc-linaro-4.5/gcc/reload1.c:6704:7: internal compiler error: Floating point exception

This is while running the all-stagefeedback-gcc stage. I see the same on x86_64 and will try it on armv7.

Michael Hope wrote on 2011-04-13:

I see similar on ARM:
 http://builds.linaro.org/toolchain/gcc-linaro-4.5+bzr99492%5Eprofiled/logs/armv7l-maverick-cbuild109-ursa1-cortexa9r1/gcc-build.txt

../../../gcc-linaro-4.5/gcc/gengtype.c: In function 'write_types_process_field':
../../../gcc-linaro-4.5/gcc/gengtype.c:2458:3: internal compiler error: in set_jump_prob, at stmt.c:2319

../../../gcc-linaro-4.5/gcc/read-rtl.c: In function 'apply_iterator_traverse':
../../../gcc-linaro-4.5/gcc/read-rtl.c:548:3: internal compiler error: Floating point exception

Michael Hope wrote on 2011-04-15:

gcc-linaro-4.6+bzr106732 bootstraps OK on i686.

Ulrich Weigand wrote on 2011-04-18:

I can confirm the failure with Linaro GCC 4.5. The problem is an integer division by zero in set_jump_prob, which is a new function added as part of a feature ported from the CodeSourcery tree:

2010-01-25 Tom de Vries <email address hidden>

        gcc/
        * stmt.c (emit_case_bit_tests): Change prototype.
        * stmt.c (struct case_bit_test): Add prob field.
        * stmt.c (get_label_prob): New function.
        * stmt.c (set_jump_prob): New function.
        * stmt.c (emit_case_bit_tests): Use get_label_prob.
        * stmt.c (emit_case_bit_tests): Set prob field.
        * stmt.c (emit_case_bit_tests): Use set_jump_prob.
        * stmt.c (expand_case): Add new args to emit_case_bit_tests invocation.
        * testsuite/gcc.dg/switch-prob.c: Add test.

This particular CodeSourcery backport is not (yet?) in Linaro GCC 4.6, therefore the problem cannot occur there.