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  • Glasgow Haskell CompilerGlasgow Haskell Compiler
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  • !1869

Reimplement unsafe coercions in terms of unsafe equality proofs

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Closed Ömer Sinan Ağacan requested to merge wip/osa1/T16893 into master Oct 03, 2019
  • Overview 350
  • Commits 1
  • Pipelines 85
  • Changes 65

See Note [Implementing unsafeCoerce] for how unsafe equality proofs and the new unsafeCoerce# are implemented.

New notes added:

  • [Checking for levity polymorphism] in CoreLint.hs
  • [Implementing unsafeCoerce] in base/Unsafe/Coerce.hs
  • [Patching magic definitions] in Desugar.hs
  • [Wiring in unsafeCoerce#] in Desugar.hs

Only breaking change in this patch is unsafeCoerce# is not exported from GHC.Exts, instead of GHC.Prim.

Fixes #17443 (closed)

Fixes #16893 (closed)

NoFib
--------------------------------------------------------------------------------
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--------------------------------------------------------------------------------
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   wheel-sieve2          -0.1%      0.0%     -0.0%     -0.0%     -0.0%
           x2n1          -0.1%      0.0%     -0.0%     -0.0%     -0.0%
--------------------------------------------------------------------------------
            Min          -0.1%      0.0%     -0.5%     -0.3%     -0.4%
            Max          -0.0%      0.0%     +0.0%     +0.0%     +0.0%
 Geometric Mean          -0.1%     -0.0%     -0.0%     -0.0%     -0.0%

Test changes

  • break006 is marked as broken, see #17833
  • The compiler allocates less when building T14683 (an unsafeCoerce#- heavy happy-generated code) on 64-platforms. Allocates more on 32-bit platforms.
Edited Feb 16, 2020 by Ömer Sinan Ağacan
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Source branch: wip/osa1/T16893