Construct constant LLVMPtr correctly #38958
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Co-authored-by: Julian Samaroo <jpsamaroo@jpsamaroo.me>
vchuravy
added
backport 1.6
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I thought this was semantically invalid in LLVM IR to form an LLVMPtr from a constant / inttoptr / reinterpret / bitcast, as it has incorrect provenance (compiler optimization behaviors). For related reading, see the recent blog post: https://www.ralfj.de/blog/2020/12/14/provenance.html |
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IIUC it is legal to use a constant/inttoptr to form a LLVMPtr, as an example see the discussion in http://llvm.org/devmtg/2018-04/slides/Lopes-Sbirlea-Pointers,%20Alias%20and%20ModRef%20Analyses.pdf that differentiates between physical and logical pointers. |
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Ah, okay, that makes sense. So it's legal to form it, and use in comparisons, you're just responsible for not dereferencing it, since it might be assumed no-alias with other memory. |
KristofferC
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Co-authored-by: Julian Samaroo <jpsamaroo@jpsamaroo.me> Co-authored-by: Julian Samaroo <jpsamaroo@jpsamaroo.me> (cherry picked from commit ec386bd)
staticfloat
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Co-authored-by: Julian Samaroo <jpsamaroo@jpsamaroo.me> Co-authored-by: Julian Samaroo <jpsamaroo@jpsamaroo.me> (cherry picked from commit ec386bd)
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Co-authored-by: Julian Samaroo <jpsamaroo@jpsamaroo.me> Co-authored-by: Julian Samaroo <jpsamaroo@jpsamaroo.me>
staticfloat
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Co-authored-by: Julian Samaroo <jpsamaroo@jpsamaroo.me> Co-authored-by: Julian Samaroo <jpsamaroo@jpsamaroo.me> (cherry picked from commit ec386bd)
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fixes #38864