* -fsanitize=shift compile error
@ 2016-09-26 23:43 Mateusz Tabaka
2016-09-27 2:32 ` Segher Boessenkool
2016-09-27 8:04 ` Mason
0 siblings, 2 replies; 4+ messages in thread
From: Mateusz Tabaka @ 2016-09-26 23:43 UTC (permalink / raw)
To: gcc-help
Hi,
I'm trying to compile this file:
int main()
{
int a = 0;
switch (a)
{
case (4 << 29):
break;
}
return 0;
}
and I get this error:
./host-x86_64-pc-linux-gnu/gcc/cc1 test.c -quiet -fsanitize=shift
test.c: In function ‘main’:
test.c:6:2: error: case label does not reduce to an integer constant
case (4 << 29):
^~~~
If I remove "-fsanitize=shift" (or change the expression to be less than
2^31) I'm able to compile above code without issues.
It is expected behavior or a known bug?
Thanks.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: -fsanitize=shift compile error
2016-09-26 23:43 -fsanitize=shift compile error Mateusz Tabaka
@ 2016-09-27 2:32 ` Segher Boessenkool
2016-09-27 8:04 ` Mason
1 sibling, 0 replies; 4+ messages in thread
From: Segher Boessenkool @ 2016-09-27 2:32 UTC (permalink / raw)
To: Mateusz Tabaka; +Cc: gcc-help
On Tue, Sep 27, 2016 at 01:43:23AM +0200, Mateusz Tabaka wrote:
> int main()
> {
> int a = 0;
> switch (a)
> {
> case (4 << 29):
> break;
> }
> return 0;
> }
>
> and I get this error:
> ./host-x86_64-pc-linux-gnu/gcc/cc1 test.c -quiet -fsanitize=shift
> test.c: In function ‘main’:
> test.c:6:2: error: case label does not reduce to an integer constant
> case (4 << 29):
> ^~~~
>
> If I remove "-fsanitize=shift" (or change the expression to be less than
> 2^31) I'm able to compile above code without issues.
> It is expected behavior or a known bug?
It is a bug, but a bug in your code: 4 << 29 is undefined behaviour
(see C11 6.5.7/4).
Segher
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: -fsanitize=shift compile error
2016-09-26 23:43 -fsanitize=shift compile error Mateusz Tabaka
2016-09-27 2:32 ` Segher Boessenkool
@ 2016-09-27 8:04 ` Mason
2016-09-27 15:50 ` Mateusz Tabaka
1 sibling, 1 reply; 4+ messages in thread
From: Mason @ 2016-09-27 8:04 UTC (permalink / raw)
To: Mateusz Tabaka; +Cc: GCC help
On 27/09/2016 01:43, Mateusz Tabaka wrote:
> I'm trying to compile this file:
> int main()
> {
> int a = 0;
> switch (a)
> {
> case (4 << 29):
> break;
> }
> return 0;
> }
>
> and I get this error:
> ./host-x86_64-pc-linux-gnu/gcc/cc1 test.c -quiet -fsanitize=shift
> test.c: In function ‘main’:
> test.c:6:2: error: case label does not reduce to an integer constant
> case (4 << 29):
Try 4u << 29
Do you get the same error?
Regards.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: -fsanitize=shift compile error
2016-09-27 8:04 ` Mason
@ 2016-09-27 15:50 ` Mateusz Tabaka
0 siblings, 0 replies; 4+ messages in thread
From: Mateusz Tabaka @ 2016-09-27 15:50 UTC (permalink / raw)
To: Mason; +Cc: GCC help
On 27.09.2016 10:04, Mason wrote:
> Try 4u << 29
That worked. Thanks!
^ permalink raw reply [flat|nested] 4+ messages in thread
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2016-09-26 23:43 -fsanitize=shift compile error Mateusz Tabaka
2016-09-27 2:32 ` Segher Boessenkool
2016-09-27 8:04 ` Mason
2016-09-27 15:50 ` Mateusz Tabaka
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