https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79479
Bug ID: 79479
Summary: -Woverflow false alarm in unreachable expression
Product: gcc
Version: 6.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: eggert at gnu dot org
Target Milestone: ---
Created attachment 40722
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40722&action=edit
gcc -m32 -Woverflow incorrectly complains about this
Compile the attached program with:
gcc -m32 -S too-large.c
and it responds:
too-large.c: In function ‘too_large’:
too-large.c:5:18: warning: integer overflow in expression [-Woverflow]
return 32768 * 65536L < x;
Since the expression 32768 * 65536L cannot be executed on this platform (and
this is by design, the code tests whether the multiplication is advisable
before trying it), the warning is a false alarm.
Bruno Haible originally reported this problem in bug-gnulib, here:
http://lists.gnu.org/archive/html/bug-gnulib/2017-02/msg00041.html
As this sort of thing is common in portable code that is checking for overflow
correctly, I suggest disabling -Woverflow tests inside unreachable expressions.
