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 5af7f4e0468eff8d86abf3b4cde85fcc2ac5de9b..270a26a5339099f15e4f87b92bab2c8b571fac64 100644 (file)
--- a/src/backend/utils/adt/network.c
+++ b/src/backend/utils/adt/network.c
@@ -1282,7 +1282,7 @@ 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);
@@ -1314,7 +1314,7 @@ 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));
@@ -1346,7 +1346,7 @@ 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));
@@ -1371,7 +1371,7 @@ 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);
@@ -1455,7 +1455,7 @@ inetmi(PG_FUNCTION_ARGS)
                unsigned char *pip2 = ip_addr(ip2);
                int                     carry = 1;
 
-               while (nb-- > 0)
+               while (--nb >= 0)
                {
                        int                     lobyte;