[Bug c/42688] New: gcc 4.3.3 with -O2 thinks a often non-zero expression is always zero

["mnemo at minimum dot se" <gcc-bugzilla at gcc dot gnu dot org>]

When you build sqlite using GCC and "-O2" parameter you get the following
warning. During runtime "EXPR_FULLSIZE-nSize" is mostly non-zero so it seems
that the GCC optimizer makes some assumptions that doesn't not always hold
true.

In function ?memset?,
    inlined from ?exprDup? at sqlite3.c:61011:
/usr/include/bits/string3.h:82: warning: call to ?__warn_memset_zero_len?
declared with attribute warning: memset used with constant zero length
parameter; this could be due to transposed parameters

Repro steps:
0. install GCC 4.3.3
1. fetch and unpack sqlite from this URL:
http://www.sqlite.org/sqlite-amalgamation-3.6.22.tar.gz
2. run "gcc -O2 sqlite3.c"

Background: this issue was originally posted to the sqlite project as a sqlite
bug but they dismissed it as a GCC bug instead (which I believe is correct):
http://www.sqlite.org/src/tktview?name=f51d950180


-- 
           Summary: gcc 4.3.3 with -O2 thinks a often non-zero expression is
                    always zero
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mnemo at minimum dot se


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42688