http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7652
Chung-Ju Wu <jasonwucj at gmail dot com> changed:
What |Removed |Added
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CC| |jasonwucj at gmail dot com
--- Comment #19 from Chung-Ju Wu <jasonwucj at gmail dot com> ---
(In reply to David Binderman from comment #17)
> (In reply to Daniel Marjamäki from comment #7)
> > In my experience this type of check is really noisy if there is a warning
> > for every fall through.
> >
> > I recommend that the warning is written only if the fall through cause
> > redundant or bad behaviour. such as:
> >
> > switch (foo) {
> > case 1: x = y; // <- redundant assignment
> > case 2: x = z;
> > };
>
> I'd be happy with gcc warning for this kind of problem.
>
> This specific case should be easier to catch than the
> general case.
I believe such redundant assignment will be optimized out.
$ gcc --version
gcc (20130621) 4.9.0 20130621 (experimental)
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ gcc -O2 -S pr7652.c
[pr7652.c]
1
2 extern int a;
3 extern int b;
4 extern int c;
5
6 int
7 main(int argc, char **argv)
8 {
9 int x;
10
11 switch (argc)
12 {
13 case 1:
14 x = a;
15 case 7:
16 x = b;
17 break;
18 default:
19 x = c;
20 break;
21 }
22
23 return x;
24 }
[pr7652.s]
1 .file "pr7652.c"
2 .section .text.startup,"ax",@progbits
3 .p2align 4,,15
4 .globl main
5 .type main, @function
6 main:
7 .LFB0:
8 .cfi_startproc
9 movl 4(%esp), %eax
10 cmpl $1, %eax
11 je .L3
12 cmpl $7, %eax
13 je .L3
14 movl c, %eax
15 ret
16 .L3:
17 movl b, %eax
18 ret
19 .cfi_endproc
20 .LFE0:
21 .size main, .-main
22 .ident "GCC: (20130621) 4.9.0 20130621 (experimental)"
23 .section .note.GNU-stack,"",@progbits
Apparently it is dead code. IMHO, it may not be a good idea to
have compiler issue a warning everytime when compiler identifies
dead code statements.
