On 11/23/21 17:37, Jakub Jelinek wrote:
On Wed, Nov 10, 2021 at 12:31:30AM +0530, Siddhesh Poyarekar wrote:
Use SSA names as placeholders self-referencing variables to generate
expressions for object sizes and then reduce those size expressions
to constants instead of repeatedly walking through statements.
This change also makes sure that object sizes for an SSA name are
updated at most twice, once if there is a dependency loop and then the
final time upon computation of object size. Iteration to deduce the
final size is now done on the size expressions instead of walking
through the object references.
Added test to include a case where __builtin_object_size incorrectly
returned the minimum object size as zero.
This feels way too risky to me. I think making some code do something
different between (x & OST_DYNAMIC) == 0 and == 1 is just fine,
it doesn't have to share everything. After all, for __bdos we actually
emit code to compute it at runtime, while for __bos we don't.
So I'd keep e.g. .pass = 0, .pass = 1 and .pass = 2 (in a loop) in
compute_builtin_object_size for non-OST_DYNAMIC and only use your new
stuff for __bdos.
E.g. creating new SSA_NAMEs for __bos doesn't look like a good idea to me.
The GCC __bos testsuite is not big enough that it covers everything and
even in it we sometimes reexamine 2, 3 or 4 times.
OK, so addr_object_size does not participate in dependency loops, so I
can keep its changes intact and simply add a INTEGER_CST check at the
end to return unknown if the size expression is not constant; we kinda
do that for object offsets anyway.
I could then make a new entry point collect_object_sizes_for (renaming
the current one to collect_static_object_sizes_for and a new one
collect_dynamic_object_sizes_for, routing based on object_size_type &
OST_DYNAMIC) which sends the object size collection down different
paths. I can reuse the object size vectors and just have different data
in them.
Would that be reasonable?
Thanks,
Siddhesh
