pgsql: Further tweak memory management for regex DFAs.

Further tweak memory management for regex DFAs.

Coverity is still unhappy after commit 190c79884, and after looking
closer I think it might be onto something. The callers of newdfa()
typically drop out if v->err has been set nonzero, which newdfa()
is faithfully doing if it fails. However, what if v->err was already
nonzero before we entered newdfa()? Then newdfa() could succeed and
the caller would promptly leak its result.

I don't think this scenario can actually happen, but the predicate
"v->err is always zero when newdfa() is called" seems difficult to be
entirely sure of; there's a good deal of code that potentially could
get that wrong.

It seems better to adjust the callers to directly check for a null
result instead of relying on ISERR() tests. This is slightly cheaper
than the previous coding anyway.

Lacking evidence that there's any real bug, no back-patch.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6c20bdb2a279086777a3595ab00bcf14671fc5a1

Modified Files
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src/backend/regex/rege_dfa.c | 2 ++
src/backend/regex/regexec.c | 18 ++++++++----------
2 files changed, 10 insertions(+), 10 deletions(-)