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pcwalton's profile
Patrick Walton
Patrick Walton
Patrick Walton
@pcwalton

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Patrick Walton

@pcwalton

Research engineer at Mozilla

San Francisco, CA
pcwalton.github.io
Joined November 2009

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    1. Shafik Yaghmour‏ @shafikyaghmour 23 Sep 2019
      • Report Tweet
      • Report NetzDG Violation

      LLVM removing stores to constant memory (which is undefined behavior): http://releases.llvm.org/9.0.0/docs/ReleaseNotes.html#noteworthy-optimizations … catches real bug: https://bugs.llvm.org/show_bug.cgi?id=42763 … #programmingpic.twitter.com/9tI6lUoSaP

      8 replies 31 retweets 114 likes
      Show this thread
    2. John Regehr‏ @johnregehr 23 Sep 2019
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      Replying to @shafikyaghmour

      ugh!!!! it doesn't catch these bugs, it exposes them in the worst way

      1 reply 0 retweets 20 likes
    3. Rich Felker‏ @RichFelker 23 Sep 2019
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      Replying to @johnregehr @shafikyaghmour

      I don't see why you'd ever drop a code path entirely as unreachable rather than just replacing it with a single insn ud2 or similar as far back as you can propagate the unconditional UB. The cost is tiny and the outcome is far better.

      2 replies 0 retweets 7 likes
    4. John Regehr‏ @johnregehr 23 Sep 2019
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      Replying to @RichFelker @shafikyaghmour

      ok I'll take the devil's side of this argument for a minute: I think we agree that "if (false)" sorts of code paths that come from config-time information are ok to drop, right?

      2 replies 0 retweets 3 likes
    5. mik‏ @mik235 23 Sep 2019
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      Replying to @johnregehr @RichFelker @shafikyaghmour

      `if (false)` produces a warning though, right? But also, that's clearly defined, but obviously unreachable. Undefined behaviour where people disagree on what the compiler should do with it :)

      1 reply 0 retweets 0 likes
    6. Stephen Checkoway‏ @stevecheckoway 23 Sep 2019
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      Replying to @mik235 @johnregehr and

      Does it? https://godbolt.org/z/L7g-d8  (I mean, sure, if you use -Wunreachable-code but since that's not in -Wall, I kinda doubt many people use it.)

      1 reply 0 retweets 1 like
    7. mik‏ @mik235 23 Sep 2019
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      Replying to @stevecheckoway @johnregehr and

      I'm sure I've seen "condition will always be" warnings a lot... maybe from some other language I write a lot in?

      1 reply 0 retweets 1 like
    8. John Regehr‏ @johnregehr 23 Sep 2019
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      Replying to @mik235 @stevecheckoway and

      you typically see this for (a>b) where the result is statically known in some trivial fashion, but it doesn't generally make sense to warn about if (false) since this is done all the time, on purpose

      1 reply 0 retweets 5 likes
      Patrick Walton‏ @pcwalton 23 Sep 2019
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      Replying to @johnregehr @mik235 and

      It’s the old Scheme joke: “Who writes that kind of code?” “Macros do.”

      7:30 PM - 23 Sep 2019
      • 14 Likes
      • asta Alexey Romanov Stephen Checkoway nick fitzgerald mik Shafik Yaghmour Sam Tobin-Hochstadt John Regehr Rich Felker
      0 replies 0 retweets 14 likes

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