Stream: git-wasmtime

Topic: wasmtime / PR #4721 Remove binary_imm64 and int_compare_i...

Wasmtime GitHub notifications bot (Aug 16 2022 at 17:12):

jameysharp opened PR #4721 from remove-imm-insts to main:

I have no idea yet whether this is a good change, and it definitely
should not be merged as-is. The main issues are that there are a bunch
of tests I haven't fixed up, and some optimizations I've removed. Also I
have no performance measurements yet to see what effect this has on
either compile time or generated code quality.

I just wanted to understand what the *_imm instructions were used for,
and trying to grep for them didn't work out well. So I removed them to
let the compiler tell me where they're used instead.

To avoid having to make as many changes, I introduced a InstImmBuilder
trait. It provides methods like iadd_imm which emit the pair of
instructions that legalization would have decomposed that instruction
into eventually anyway.

I have several questions that this may help with answering:

• Is there significant savings, in IR code size and/or compile time,
  from inlining one immediate operand into some instructions at the
  frontend? Or is the widespread frontend use of these instructions just
  for convenience?

• Can simple_preopt cleanly identify arithmetic identities involving
  constants without rewriting to use these combined forms?

• Is there a compile-time cost to simple_preopt rewriting into combined
  forms, only for legalization to rewrite them away again soon after?

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Wasmtime GitHub notifications bot (Aug 16 2022 at 20:13):

jameysharp updated PR #4721 from remove-imm-insts to main.

Last updated: Dec 23 2024 at 12:05 UTC