https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100702
Bug ID: 100702
Summary: Strict overflow warning regression in gcc 8 onwards
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: david at westcontrol dot com
Target Milestone: ---
Incorrect code like this example relies on two's complement wrapping to do what
the programmer wanted:
void foo(int *a)
{
int i;
for (i=0; i<i+1; i++)
a[i&256]=0;
}
Since signed integer overflow is undefined behaviour, gcc optimises code like
that to an infinite loop. That's fair enough. But it would always be helpful
with a warning about such cases.
For gcc 7 and below, gcc can generate a warning but only if
"-Wstrict-overflow=5" is used.
gcc 8 and above have no warning, even with that flag (and -Wall -Wextra -O2).
I realise that these things can change between versions due to re-arrangement
of compiler passes and other differences. But is there a possibility of a
warning when assumptions about undefined behaviour lead to infinite loops?
(The compiler knows the loop is infinite - it doesn't bother generating a
return opcode.)
