Wasmtime GitHub notifications bot (Jun 15 2020 at 21:34): Wasmtime GitHub notifications bot (Jun 15 2020 at 21:34):fitzgen opened Issue #1883:
Enabling stack maps and GC safepoints adds another pass over the IR (
emit_stackmaps) regardless whether the function in question actually uses reference types at all. One could imagine (especially with wasm-bindgen's "switch reference types into table indices at the boundaries" approach, that seems likely to be copied by C/C++) that many functions in a module don't use reference types. For these functions, that extra pass over the IR is a waste of time.We could have a flag on functions that gets set if it uses reference types in any way (and then never gets unset when a particular reference type-using instruction is removed, so we don't have to precisely count them) and in
emit_stackmaps, only walk the IR if the flag is set (and probablydebug_assert!that it doesn't have any uses of reference types if the flag is not set).This came up in https://github.com/bytecodealliance/wasmtime/pull/1832#discussion_r440456291 for Wasmtime.
Wasmtime GitHub notifications bot (Jun 15 2020 at 21:34):fitzgen labeled Issue #1883:
Enabling stack maps and GC safepoints adds another pass over the IR (
emit_stackmaps) regardless whether the function in question actually uses reference types at all. One could imagine (especially with wasm-bindgen's "switch reference types into table indices at the boundaries" approach, that seems likely to be copied by C/C++) that many functions in a module don't use reference types. For these functions, that extra pass over the IR is a waste of time.We could have a flag on functions that gets set if it uses reference types in any way (and then never gets unset when a particular reference type-using instruction is removed, so we don't have to precisely count them) and in
emit_stackmaps, only walk the IR if the flag is set (and probablydebug_assert!that it doesn't have any uses of reference types if the flag is not set).This came up in https://github.com/bytecodealliance/wasmtime/pull/1832#discussion_r440456291 for Wasmtime.
Wasmtime GitHub notifications bot (Jun 15 2020 at 21:35):github-actions[bot] commented on Issue #1883:
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Wasmtime GitHub notifications bot (Jun 17 2020 at 14:09):bnjbvr commented on Issue #1883:
Thanks for opening an issue! Do you have any numbers on how much relative time is spent going over the IR, for a large module? This would help quantifying how urgent an issue it is. In any case, agreed that not doing wasteful work is generally good, of course.
The idea of using a flag on the function sounds good. Not sure where to put it, since as far as i can tell it's the first usage of a flag in a Function; could be directly there, or DataFlowGraph, etc.
Wasmtime GitHub notifications bot (Jun 17 2020 at 15:54):fitzgen commented on Issue #1883:
Not sure how much time is spent doing the pass when there aren't any reference types used, it just came up during review.
Wasmtime GitHub notifications bot (Aug 08 2020 at 00:41):fitzgen closed Issue #1883:
Enabling stack maps and GC safepoints adds another pass over the IR (
emit_stackmaps) regardless whether the function in question actually uses reference types at all. One could imagine (especially with wasm-bindgen's "switch reference types into table indices at the boundaries" approach, that seems likely to be copied by C/C++) that many functions in a module don't use reference types. For these functions, that extra pass over the IR is a waste of time.We could have a flag on functions that gets set if it uses reference types in any way (and then never gets unset when a particular reference type-using instruction is removed, so we don't have to precisely count them) and in
emit_stackmaps, only walk the IR if the flag is set (and probablydebug_assert!that it doesn't have any uses of reference types if the flag is not set).This came up in https://github.com/bytecodealliance/wasmtime/pull/1832#discussion_r440456291 for Wasmtime.
Last updated: Dec 23 2024 at 12:05 UTC