[llvm-dev] [llvm v3.6.2+] BROKEN: g++-4.9: error: unrecognized command line option '-Wcovered-switch-default'

Fri Sep 4 00:59:00 PDT 2015

Hi,

I try to compile LLVM/Clang v3.6.2 with gcc/g++ v4.9, this fails after
configure like this...

[ build-log]
...
llvm[0]: Constructing LLVMBuild project information.
make[1]: Entering directory
`/home/wearefam/src/llvm-toolchain/llvm-build/lib/Support'
llvm[1]: Compiling APFloat.cpp for Release+Asserts build
g++-4.9: error: unrecognized command line option '-Wcovered-switch-default'
/bin/rm: cannot remove
`/home/wearefam/src/llvm-toolchain/llvm-build/lib/Support/Release+Asserts/APFloat.d.tmp':
No such file or directory
make[1]: *** [/home/wearefam/src/llvm-toolchain/llvm-build/lib/Support/Release+Asserts/APFloat.o]
Error 1
make[1]: Leaving directory
`/home/wearefam/src/llvm-toolchain/llvm-build/lib/Support'
...

'-Wcovered-switch-default' is really an unrecognized command line
option for g++, but it is set after configure has done its work (see
[1]).

[ configure-log ]
...
checking optional compiler flags... -Wno-variadic-macros
-Wno-missing-field-initializers -Wcovered-switch-default
-Wno-uninitialized  -Wno-comment
...

Why is '-Wcovered-switch-default' set? It is unrecognized!

Not sure if this workaround below is good or not.

[ llvm/autoconf/configure.ac ]
...
dnl Check optional compiler flags.
AC_MSG_CHECKING([optional compiler flags])
CXX_FLAG_CHECK(NO_VARIADIC_MACROS, [-Wno-variadic-macros])
CXX_FLAG_CHECK(NO_MISSING_FIELD_INITIALIZERS, [-Wno-missing-field-initializers])
# XXX: Workaround: g++-4.9: error: unrecognized command line option
'-Wcovered-switch-default'
if test "$GXX" = "yes"
  COVERED_SWITCH_DEFAULT=
else
CXX_FLAG_CHECK(COVERED_SWITCH_DEFAULT, [-Wcovered-switch-default])
fi
...

I checked Wild Wild Internet, but what is the adequate command line
option for g++?

I followed the BR in [3] and [4] gave no clear information on this.

GCC online-docs [1] lists these warning-options:
...
[ -Wswitch ]
Warn whenever a switch statement has an index of enumerated type and
lacks a case for one or more of the named codes of that enumeration.
(The presence of a default label prevents this warning.) case labels
outside the enumeration range also provoke warnings when this option
is used (even if there is a default label). This warning is enabled by
-Wall.

[ -Wswitch-default ]
Warn whenever a switch statement does not have a default case.

[ -Wswitch-enum ]
Warn whenever a switch statement has an index of enumerated type and
lacks a case for one or more of the named codes of that enumeration.
case labels outside the enumeration range also provoke warnings when
this option is used. The only difference between -Wswitch and this
option is that this option gives a warning about an omitted
enumeration code even if there is a default label.

[ -Wswitch-bool ]
Warn whenever a switch statement has an index of boolean type and the
case values are outside the range of a boolean type. It is possible to
suppress this warning by casting the controlling expression to a type
other than bool. For example:

          switch ((int) (a == 4))
            {
            ...
            }

This warning is enabled by default for C and C++ programs.
...

In my workaround-snippet I unset COVERED_SWITCH_DEFAULT.

Comments?

Thanks in advance.

Regards,
- Sedat -

P.S.: I have attached my build-script and the outputs of my configure
and build logs.

[1] https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
[2] http://stackoverflow.com/questions/5402745/gcc-switch-on-enum-retain-missing-warning-but-use-default
[3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61864
[4] http://programmers.stackexchange.com/questions/179269/why-does-clang-llvm-warn-me-about-using-default-in-a-switch-statement-where-all/242896#242896
-------------- next part --------------
llvm[0]: Constructing LLVMBuild project information.
make[1]: Entering directory `/home/wearefam/src/llvm-toolchain/llvm-build/lib/Support'
llvm[1]: Compiling APFloat.cpp for Release+Asserts build
g++-4.9: error: unrecognized command line option '-Wcovered-switch-default'
/bin/rm: cannot remove `/home/wearefam/src/llvm-toolchain/llvm-build/lib/Support/Release+Asserts/APFloat.d.tmp': No such file or directory
make[1]: *** [/home/wearefam/src/llvm-toolchain/llvm-build/lib/Support/Release+Asserts/APFloat.o] Error 1
make[1]: Leaving directory `/home/wearefam/src/llvm-toolchain/llvm-build/lib/Support'
make: *** [all] Error 1
-------------- next part --------------
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