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馃洡 Non-trapping float-to-int conversions #11

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binji opened this Issue Oct 16, 2018 · 0 comments

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binji commented Oct 16, 2018

This is a tracking issue for a post-MVP feature
It will be updated as the issue progresses.

Topic Non-trapping float-to-int conversions
Champion Dan Gohman @sunfishcode
Status in progress
Phase Implementation phase
Linked issues WebAssembly/design#986, WebAssembly/design#1089
Linked repositories github.com/WebAssembly/nontrapping-float-to-int-conversions

Details

The primary motivations are:

  • LLVM鈥檚 float-to-int conversion has an undefined result, rather than undefined behavior, and it seems LLVM does speculate it under certain conditions.
  • For the SIMD proposal, it鈥檚 more SIMD-hardware-like if no SIMD operations trap. This proposal would establish a convention for saturating operations which SIMD could share, to avoid introducing trapping.

This proposal is not motivated by performance data.

It's plausible that LLVM could be changed, to have something like an "nsw" flag for the "fptosi" instruction, especially with some of the recent proposals to modify the poison concept in LLVM. However, no one is currently working on this.

@WebAssembly WebAssembly locked and limited conversation to collaborators Oct 16, 2018

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