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Remove unnecessary extend instructions #1147

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merged 2 commits into from
Aug 1, 2024
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@Robbepop Robbepop commented Aug 1, 2024

The Wasm i64_extend_i32_u and i64_extend_i32_s instructions are unnecessary in Wasmi bytecode.

  • The i64_extend_i32_u instruction is essentially a no-op in an untyped bytecode.
  • The i64_extend_i32_s instruction can be replaced by the i64_extend32_s instruction since Wasmi bytecode is untyped and the only difference between these two instructions is their effect on the type system.

Technically the i32_wrap_i64 x instruction could be replaced by i64.and x 0xFFFF_FFFF but due to Wasmi's current bytecode encoding this replacement representation would require substantially more encoding space and was less efficient.

The Wasm i64_extend_i32_u and i64_extend_i32_s instructions are unnecessary in Wasmi bytecode since they can be replaced entirely by the sign-extension instructions. This is possible since Wasmi bytecode is untyped during execution and the only different between those instructions is their effect on the type system.
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codecov bot commented Aug 1, 2024

Codecov Report

Attention: Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.80%. Comparing base (0a6a083) to head (9f90837).

Files Patch % Lines
crates/wasmi/src/engine/translator/mod.rs 88.88% 1 Missing ⚠️
Additional details and impacted files
@@            Coverage Diff             @@
##             main    #1147       /-   ##
==========================================
  Coverage   79.78%   79.80%    0.01%     
==========================================
  Files         296      296              
  Lines       25422    25424        2     
==========================================
  Hits        20284    20289        5     
  Misses       5138     5135       -3     

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@Robbepop Robbepop merged commit 8d0f733 into main Aug 1, 2024
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@Robbepop Robbepop deleted the rf-remove-unnecessary-casts branch August 1, 2024 09:51
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