On 7/30/19 6:20 AM, Jan de Mooij wrote:
On Tue, Jul 30, 2019 at 1:51 PM ISHIKAWA,chiaki <ishik...@yk.rim.or.jp>
wrote:
nsresult rv2
= NS_NewBufferedOutputStream(getter_AddRefs(mCopyState->m_fileStream),
mCopyState->m_fileStream.forget(), <=== It seems this can be nullptr in
clang-8 version???
64 * 1024 );
This looks like it could be caused by Clang evaluating your arguments in a
different order from GCC (see also [0]). If Clang evaluates left-to-right,
that getter_AddRefs might null out your m_fileStream before we evaluate the
m_fileStream.forget().
Note that, if I'm reading the spec correctly, it's not just the order of
evaluation between arguments. Before c++17, the evaluation of different
arguments could be interleaved arbitrarily. It looks like c++17 changes
argument evaluation to be "indeterminately sequenced" instead of the
previous "unsequenced". Indeterminately sequenced means they can happen
in any order, but *cannot* be interleaved as they are now. I don't think
that comes up in your specific example, but it's closely related.
https://en.cppreference.com/w/cpp/language/eval_order
I know the interleaving happens in practice because the GC rooting
hazard analysis ran into this: a Rooted value passed to a function was
extracted into a temporary, another argument's evaluation triggered a GC
that moved the value, and then the now-invalid temporary was passed into
the function. It looks like c++17 will prevent this from happening.
I guess that gives me motivation to finish updating the rooting analysis
to gcc8, which has c++17 support. Which is relevant to you, since you're
compiling with gcc: the minimum gcc version is going to be bumped to
gcc7 soon, and it looks like we'll only be testing with gcc8 in the
continuous integration system, so it would be safest to use a minimum of
gcc 8. (gcc 7.4.0 has a bug that breaks the rooting analysis, so it will
go straight to gcc 8.)
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