Root table items; reverse table/elem edge directions #153
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The function table contains functions that can be dynamically indirectly called, and since we can't statically understand indirect calls (and nor can the linker or wasm-gc) we treat the table as roots (effectively rooting anything that the table is holding). Fixes #5
It was the other way around because at the binary level the element references which table it is populating, but logically it is the table that owns its elements. It gives us much more useful data this way: we can see when the table is heavy in the dominators tree, because a bunch of dynamic indirect calls that the linker couldn't remove got entrenched in the binary.
data-pup
reviewed
Sep 7, 2018
| @@ -559,7 +559,7 @@ impl<'a> Parse<'a> for elements::ElementSection { | |||
| let elem_id = Id::entry(idx, i); | |||
| if let Some(table_section_idx) = table_section_idx { | |||
| let entry_id = Id::entry(table_section_idx, elem.index() as usize); | |||
| items.add_edge(elem_id, entry_id); | |||
| items.add_edge(entry_id, elem_id); | |||
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logically it is the table that owns its
elements. It gives us much more useful data this way: we can see when the table
is heavy in the dominators tree, because a bunch of dynamic indirect calls that
the linker couldn't remove got entrenched in the binary.
It took a second for me to understand this, but ❗ omg! ❗
Would not have thought of this, ! This is so cool :)
data-pup
approved these changes
Sep 7, 2018
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Muuuuch less reported in
twiggy garbagenow :)And tables are showing up as expected in the dominator trees now!