Stream: git-wasmtime

Topic: wasmtime / issue #5031 cranelift: Remove booleans

view this post on Zulip Wasmtime GitHub notifications bot (Oct 12 2022 at 20:00):

elliottt commented on issue #5031:

@uweigand, could you take a closer look at my changes to the s390x backend? In particular the changes in c01d860, as they increased the instruction count for the bmask translation by quite a bit.

view this post on Zulip Wasmtime GitHub notifications bot (Oct 12 2022 at 22:32):

elliottt edited a comment on issue #5031:

@uweigand, could you take a closer look at my changes to the s390x backend? In particular the changes to the lowering of bmask, as they increased the instruction count for the translation by quite a bit.

view this post on Zulip Wasmtime GitHub notifications bot (Oct 13 2022 at 09:35):

uweigand commented on issue #5031:

@uweigand, could you take a closer look at my changes to the s390x backend? In particular the changes to the lowering of bmask, as they increased the instruction count for the translation by quite a bit.

Well, in part this is due to changed semantics: the old bmask would take a boolean type as input, which (except for $B1) already used only the values 0 and -1. So the semantics of bmask was simply a no-op or a sign-extend. The new bmask I understand now needs to take any arbitrary integer input, so it actually has to perform a comparison against zero.

That said, I think the new implementation could still be improved, in particular the $I128 cases. However, instead of re-implementing the wheel here, why don't you simply use the existing icmp_val helper to emit the actual comparison?

Maybe something alone the lines of

 (rule (lower (has_type oty (bmask x @ (value_type ity))))
       (lower_bool_to_mask oty (icmp_val $true (IntCC.NotEqual) x (imm ity 0)))

with a new helper lower_bool_to_mask analogous to the old lower_bool ...

view this post on Zulip Wasmtime GitHub notifications bot (Oct 13 2022 at 10:20):

uweigand commented on issue #5031:

Following up on myself, it would be even simpler and better to use the existing value_nonzero helper, which will fold in previous comparisons if possible:

 (rule (lower (has_type ty (bmask x)))
       (lower_bool_to_mask ty (value_nonzero x)))

view this post on Zulip Wasmtime GitHub notifications bot (Oct 13 2022 at 15:25):

elliottt commented on issue #5031:

Following up on myself, it would be even simpler _and_ better to use the existing value_nonzero helper, which will fold in previous comparisons if possible:

(rule (lower (has_type ty (bmask x))) (lower_bool_to_mask ty (value_nonzero x)))

This is much nicer! I'll rework the changes to add lower_bool_to_mask instead.

view this post on Zulip Wasmtime GitHub notifications bot (Oct 13 2022 at 17:13):

uweigand commented on issue #5031:

This is much nicer! I'll rework the changes to add lower_bool_to_mask instead.

Thanks! The s390x parts LGTM now.

Last updated: Dec 13 2025 at 19:03 UTC