Paul Eggert wrote:
> the warning is not emitted if the program simply does this instead:
>
> int x; x = 10;
>
Indeed: While
===========================================================
extern void bar (int);
int foo (int a)
{
if (a == 1) goto one;
int b = 4;
bar (b);
one:
return a;
}
===========================================================
produces a warning,
===========================================================
extern void bar (int);
int foo (int a)
{
if (a == 1) goto one;
int b; b = 4;
bar (b);
one:
return a;
}
===========================================================
does not.
> That is, although it's natural when seeing this line:
>
> int x = 10;
>
> to assume that X must always be initialized, this assumption is incorrect if
> a
> goto jumps over the declaration.
If this was the purpose, why do we get a warning in my first example, where
'b' is not used after label 'one:'?
And when 'b' is used after the label: Tim's example
===========================================================
extern int bar (int);
int foo (int a)
{
if (a == 1) goto one;
int b = bar (a);
one:
return b;
}
===========================================================
produces a warning.
But this variation
===========================================================
extern int bar (int);
int foo (int a)
{
if (a == 1) goto one;
int b; b = bar (a);
one:
return b;
}
===========================================================
gives no warning. THIS IS THE DANGEROUS CASE. To get a warning on
this one, use -O -Wmaybe-uninitialized.
Jim Meyering wrote:
> Didn't this warning or one very much like it catch real bugs, e.g.,
> where the initialization would be omitted, and the result would be to
> use an uninitialized variable somewhere after the jumped-to label?
The warning options that catches real bugs is -Wuninitialized
-Wmaybe-uninitialized (part of -Wall) in combination with -O.
I conclude that the only point of this warning is to help people write code
that can be compiled with a C++ compiler. Which is why it is included in
-Wc++-compat.
Paul Eggert wrote:
> so it does seem a bit ridiculous to enable the warning, and it'd be fine with
> me
> if we removed it from manywarnings.
OK, done as follows:
2018-06-25 Bruno Haible <br...@clisp.org>
manywarnings: Don't enable -Wjump-misses-init warnings by default.
* build-aux/gcc-warning.spec: Add -Wjump-misses-init.
* m4/manywarnings.m4 (gl_MANYWARN_ALL_GCC(C)): Remove
-Wjump-misses-init.
diff --git a/build-aux/gcc-warning.spec b/build-aux/gcc-warning.spec
index e2625ea..c47298e 100644
--- a/build-aux/gcc-warning.spec
+++ b/build-aux/gcc-warning.spec
@@ -18,7 +18,7 @@
-Warray-bounds=<0,2> handled specially by gl_MANYWARN_ALL_GCC
-Warray-temporaries fortran
-Wassign-intercept objc/objc++
--Wc++-compat FIXME maybe? borderline. some will
want this
+-Wc++-compat only useful for code meant to be
compiled by a C++ compiler
-Wc++0x-compat c++
-Wc++11-compat c++
-Wc++14-compat c++
@@ -65,6 +65,7 @@
-Wintrinsic-shadow fortran
-Wintrinsics-std fortran
-Winvalid-offsetof c++ and objc++
+-Wjump-misses-init only useful for code meant to be
compiled by a C++ compiler
-Wlarger-than- gcc --help=warnings artifact
-Wlarger-than=<number> FIXME: choose something sane?
-Wline-truncation fortran
diff --git a/m4/manywarnings.m4 b/m4/manywarnings.m4
index 350c135..925c40e 100644
--- a/m4/manywarnings.m4
+++ b/m4/manywarnings.m4
@@ -1,4 +1,4 @@
-# manywarnings.m4 serial 14
+# manywarnings.m4 serial 15
dnl Copyright (C) 2008-2018 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
@@ -108,7 +108,7 @@ m4_defun([gl_MANYWARN_ALL_GCC(C)],
# comm -3 \
# <((sed -n 's/^ *\(-[^ 0-9][^ ]*\) .*/\1/p' manywarnings.m4; \
# awk '/^[^#]/ {print $1}' ../build-aux/gcc-warning.spec) | sort) \
- # <(gcc --help=warnings | sed -n 's/^ \(-[^ ]*\) .*/\1/p' | sort)
+ # <(LC_ALL=C gcc --help=warnings | sed -n 's/^ \(-[^ ]*\) .*/\1/p' | sort)
gl_manywarn_set=
for gl_manywarn_item in -fno-common \
@@ -174,7 +174,6 @@ m4_defun([gl_MANYWARN_ALL_GCC(C)],
-Wint-to-pointer-cast \
-Winvalid-memory-model \
-Winvalid-pch \
- -Wjump-misses-init \
-Wlogical-not-parentheses \
-Wlogical-op \
-Wmain \
