Work around spurious compiler warning in inet operators

gcc 12+ has complaints like the following:

../../../../../pgsql/src/backend/utils/adt/network.c: In function 'inetnot':
../../../../../pgsql/src/backend/utils/adt/network.c:1893:34: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1893 |                         pdst[nb] = ~pip[nb];
      |                         ~~~~~~~~~^~~~~~~~~~
../../../../../pgsql/src/include/utils/inet.h:27:23: note: at offset -1 into destination object 'ipaddr' of size 16
   27 |         unsigned char ipaddr[16];       /* up to 128 bits of address */
      |                       ^~~~~~
../../../../../pgsql/src/include/utils/inet.h:27:23: note: at offset -1 into destination object 'ipaddr' of size 16

This is due to a compiler bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104986

It has been a year since the bug has been reported without getting fixed. As
the warnings are verbose and use of gcc 12 is becoming more common, it seems
worth working around the bug. Particularly because a simple reformulation of
the loop condition fixes the issue and isn't any less readable.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Author: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/144536.1648326206@sss.pgh.pa.us
Backpatch: 11-

diff --git a/src/backend/utils/adt/network.c b/src/backend/utils/adt/network.c
index 0ab54316f8eaf2dcebbe779fee0fe6355e452a23..60c2b761751176a56d5c5ca73a0afff87c1c0d2e 100644 (file)
--- a/src/backend/utils/adt/network.c
+++ b/src/backend/utils/adt/network.c
@@ -1889,7 +1889,7 @@ inetnot(PG_FUNCTION_ARGS)
        unsigned char *pip = ip_addr(ip);
        unsigned char *pdst = ip_addr(dst);
 
-       while (nb-- > 0)
+       while (--nb >= 0)
            pdst[nb] = ~pip[nb];
    }
    ip_bits(dst) = ip_bits(ip);
@@ -1921,7 +1921,7 @@ inetand(PG_FUNCTION_ARGS)
        unsigned char *pip2 = ip_addr(ip2);
        unsigned char *pdst = ip_addr(dst);
 
-       while (nb-- > 0)
+       while (--nb >= 0)
            pdst[nb] = pip[nb] & pip2[nb];
    }
    ip_bits(dst) = Max(ip_bits(ip), ip_bits(ip2));
@@ -1953,7 +1953,7 @@ inetor(PG_FUNCTION_ARGS)
        unsigned char *pip2 = ip_addr(ip2);
        unsigned char *pdst = ip_addr(dst);
 
-       while (nb-- > 0)
+       while (--nb >= 0)
            pdst[nb] = pip[nb] | pip2[nb];
    }
    ip_bits(dst) = Max(ip_bits(ip), ip_bits(ip2));
@@ -1978,7 +1978,7 @@ internal_inetpl(inet *ip, int64 addend)
        unsigned char *pdst = ip_addr(dst);
        int         carry = 0;
 
-       while (nb-- > 0)
+       while (--nb >= 0)
        {
            carry = pip[nb] + (int) (addend & 0xFF) + carry;
            pdst[nb] = (unsigned char) (carry & 0xFF);
@@ -2062,7 +2062,7 @@ inetmi(PG_FUNCTION_ARGS)
        unsigned char *pip2 = ip_addr(ip2);
        int         carry = 1;
 
-       while (nb-- > 0)
+       while (--nb >= 0)
        {
            int         lobyte;