Le 2024-06-26 à 18 h 01, David Malcolm a écrit :
On Wed, 2024-02-21 at 14:16 -0500, Antoni Boucher wrote:
On Thu, 2023-12-07 at 19:57 -0500, David Malcolm wrote:
On Thu, 2023-12-07 at 17:26 -0500, Antoni Boucher wrote:
Hi.
This patch fixes getting the size of size_t (bug 112910).
There's one issue with this patch: like every other feature that
checks
for target-specific stuff, it requires a compilation before
actually
fetching the size of the type.
Which means that getting the size before a compilation might be
wrong
(and I actually believe is wrong on x86-64).
I was wondering if we should always implicitely do the first
compilation to gather the correct info: this would fix this issue
and
all the others that we have due to that.
I'm not sure what would be the performance implication.
Maybe introduce a new class target_info which contains all the
information we might want to find via a compilation, and have the
top-
level recording::context have a pointer to it, which starts as
nullptr,
but can be populated on-demand the first time something needs it?
That would mean that we'll need to populate it for every top-level
context, right? Would the idea be that we should then use child
contexts to have the proper information filled?
If so, how is this different than just compiling two contexts like
what
I currently do?
This would also mean that we'll do an implicit compilation whenever
we
use an API that needs this info, right? Wouldn't that be unexpected?
I was thinking a compilation with an empty playback::context to lazily
capture the target data.
I'm still not sure I understand what you mean.
Do you mean having a global context that we can compile to then fetch
the size of the types?
If not, could you please provide an example with some code?
I'm wondering if we could have something that would also work for custom
types like structs.
I'm also not sure what would happen if options that change the size of
types (like -m32) are provided by the user.
Is the way libgccjit currently work (with 2 phases: recording and
playback) this way because gcc is not thread-safe?
If we could directly create GENERIC trees, we could get the size from
those, but it seems like this would not be possible.
My hope was that this would make things easier for users. But you're
the one using this API, so if you're more comfortable with the explicit
initial compilation approach, let's go with that.
If so, this is OK for trunk - but we might want to add a note to the
documentation about the double-compilation workaround.
Dave
Thanks for the idea.
Another solution that I have been thinking about for a while now
would
be to have another frontend libgccaot (I don't like that name),
which
is like libgccjit but removes the JIT part so that we get access
to
the
target stuff directly and would remove the need for having a
seperation
between recording and playback as far as I understand.
That's a long-term solution, but I wanted to share the idea now
and
gather your thoughts on that.
FWIW the initial version of libgccjit didn't have a split between
recording and playback; instead the client code had to pass in a
callback to call into the various API functions (creating tree
nodes).
See:
https://gcc.gnu.org/legacy-ml/gcc-patches/2013-10/msg00228.html
Dave
