Wunused-value and Wextra interaction (PR7651 Define -Wextra strictly in terms of other warning flags)

["Manuel LÃpez-IbÃÃez" <lopezibanez at gmail dot com>]

:ADDPATCH c++:

This patch continues the effort to fix PR7651 [1].

Currently, Wextra warns when an expression-statement or the left-hand
side of a comma expression contains no side effects. However, as it is
currently implemented, the same warning is enabled by -Wunused-value,
which in turn is enabled by -Wall.

The following patch removes the warning from Wextra and expands the
description of Wunused-value to mention this particular case. It also
unifies the code that handles the warning for C and C++ into a single
function in c-common.c.

A noteworthy difference between C and C++ implementations is that C++
front-end does not emit the warning for empty statements
(IS_EMPTY_STMT). I have favoured the C implementation that does not
check for this (since there are instances in the testsuite of such
cases while there is no test checking the behaviour of the C++
front-end). Is there any rationale for not emitting the warning for
empty statements in C++?

Bootstrapped and regression tested with --enable-languages=all on
i686-pc-linux-gnu.

OK for mainline?

[1] http://gcc.gnu.org/ml/gcc-patches/2006-12/msg01103.html

2007-01-05  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>

 PR middle-end/7651
 * doc/invoke.texi (Wunused-value): Update description.
    (Wextra): Delete item.
 * opts.c (set_Wextra): Don't use the value of Wextra to set the
value of Wunused-value.
 * c-typeck.c (c_process_expr_stmt): Don't check extra_warnings.
 (c_finish_stmt_expr): Don't check extra_warnings.
 (emit_side_effect_warnings): Move function to...
 * c-common.c (emit_side_effect_warnings): ... here.
 * c-common.h (emit_side_effect_warnings): Declare.

cp/
2007-01-05  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>

 PR middle-end/7651
 * cp-gimplify.c (gimplify_expr_stmt): Call emit_side_effect_warnings
in c-common.c. Don't check extra_warnings.

Attachment: wunused-wextra.diff
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