On Mon, 10 Mar 2008, Tom Lane wrote:
I am wondering if these checks have been no-ops in Postgres builds done
with gcc 4.1 and up, and we're only just now being told about it.
Since gcc 4.2 supports -Wstrict-overflow, I rebuilt pg with that to see
what it's doing currently. I'm not sure what -Wstrict-overflow level
-Wall implies with gcc 4.3, but I cranked it up to 5 on 4.2 to get the
most details out of it. I don't see any of the warnings I saw on 4.3 and
I get the attached list which looks less dangerous spot checking a couple
items, but I haven't gone through the whole list.
Additionally the comments in the blog posting[1] I linked to previously, a
user asks, how come I don't see any warnings with -Wstrict-overflow on
gcc 4.2.3 and it's answered I think the full effects only come in on gcc
mainline. At least, gcc 4.2 does not eliminate the loop, but gcc 4.3
will. So clearly 4.3 is doing something new here, but that doesn't prove
we're safe on previous versions.
[1] http://www.airs.com/blog/archives/120
Kris Jurka
exec.c:245: warning: assuming signed overflow does not occur when changing X +-
C1 cmp C2 to X cmp C1 +- C2
exec.c:245: warning: assuming signed overflow does not occur when changing X +-
C1 cmp C2 to X cmp C1 +- C2
localtime.c:322: warning: assuming signed overflow does not occur when changing
X +- C1 cmp C2 to X cmp C1 +- C2
localtime.c:814: warning: assuming signed overflow does not occur when changing
X +- C1 cmp C2 to X cmp C1 +- C2
pgtz.c:480: warning: assuming signed overflow does not occur when distributing
negation across division
pgtz.c:492: warning: assuming signed overflow does not occur when distributing
negation across division
pgtz.c:503: warning: assuming signed overflow does not occur when distributing
negation across division
zic.c:862: warning: assuming signed overflow does not occur when simplifying
conditional to constant
heaptuple.c:1018: warning: assuming signed overflow does not occur when
simplifying / or % to or
heaptuple.c:1845: warning: assuming signed overflow does not occur when
simplifying / or % to or
heaptuple.c:907: warning: assuming signed overflow does not occur when
simplifying / or % to or
gram.y:9471: warning: assuming signed overflow does not occur when simplifying
conditional to constant
gistutil.c:185: warning: assuming signed overflow does not occur when changing
X +- C1 cmp C2 to X cmp C1 +- C2
gistutil.c:307: warning: assuming signed overflow does not occur when changing
X +- C1 cmp C2 to X cmp C1 +- C2
gistutil.c:417: warning: assuming signed overflow does not occur when changing
X +- C1 cmp C2 to X cmp C1 +- C2
parse_node.c:70: warning: assuming signed overflow does not occur when changing
X +- C1 cmp C2 to X cmp C1 +- C2
copy.c:2613: warning: assuming signed overflow does not occur when changing X
+- C1 cmp C2 to X cmp C1 +- C2
gistsplit.c:494: warning: assuming signed overflow does not occur when changing
X +- C1 cmp C2 to X cmp C1 +- C2
tuptoaster.c:1017: warning: assuming signed overflow does not occur when
simplifying / or % to or
tuptoaster.c:590: warning: assuming signed overflow does not occur when
simplifying / or % to or
nbtutils.c:74: warning: assuming signed overflow does not occur when changing X
+- C1 cmp C2 to X cmp C1 +- C2
freespace.c:1567: warning: assuming signed overflow does not occur when
simplifying division
freespace.c:1568: warning: assuming signed overflow does not occur when
simplifying division
freespace.c:1637: warning: assuming signed overflow does not occur when
simplifying division
freespace.c:1638: warning: assuming signed overflow does not occur when
simplifying division
arrayfuncs.c:2837: warning: assuming signed overflow does not occur when
simplifying / or % to or
arrayfuncs.c:2701: warning: assuming signed overflow does not occur when
simplifying / or % to or
dict.c:63: warning: assuming signed overflow does not occur when simplifying
multiplication
arrayfuncs.c:314: warning: assuming signed overflow does not occur when
simplifying / or % to or
cash.c:312: warning: assuming signed overflow does not occur when negating a
division
spell.c:1181: warning: assuming signed overflow does not occur when simplifying
multiplication
deadlock.c:790: warning: assuming signed overflow does not occur when
simplifying conditional to constant
spell.c:1119: warning: assuming signed overflow does not occur when simplifying
conditional to constant
s_lock.c:150: warning: assuming signed overflow does not occur when changing X
+- C1 cmp C2 to X cmp C1 +- C2
s_lock.c:155: warning: assuming signed overflow does not occur when changing X
+- C1 cmp C2 to X cmp C1 +- C2
datetime.c:2072: warning: assuming signed overflow does not occur when
simplifying conditional to constant
format_type.c:408: warning: assuming signed overflow does not occur when
simplifying / or % to or
int.c:1130: warning: assuming signed overflow does not occur when simplifying
