Wrong codegen involving uninitialized static array when compiled in release mode

[asterite]

class Context
  @block = uninitialized UInt8[1]
  @index = 0

  def result
    @block[@index] = 0_u8

    w = [0]

    int = uninitialized UInt32[1]
    int[0] = 0x67452301_u32
    int[0] += w[0]

    res = uninitialized UInt8[4]
    res[0] = (int[0] >> 8).to_u8
    res[1] = 0_u8
    res[2] = 0_u8
    res[3] = 0_u8
    res
  end
end

LibC.printf "%d\n", Context.new.result[0]
Context.new.result

Only on linux, running it in normal mode and release mode gives me 35 and 32 respectively.

[asterite]

Might be a big in LLVM. Somebody should try this with LLVM 3.8 or LLVM 3.9, because the Crystal I'm using is probably using LLVM 3.6 because it comes bundled from the omnibus release.

[RX14]

I get this using LLVM 3.9 on master: https://aww.moe/flxzvf.txt

[RX14]

Looks like a null pointer finalizer to me.

[asterite]

@RX14 I mean, if you compile just the above program with LLVM 3.9 in normal and release mode, do you get the same results?

[kostya]

llvm-config --version
3.8.1
crystal 1.cr
35
crystal 1.cr --release
35

[asterite]

@kostya Thank you! What if you use LLVM 3.5 or LLVM 3.6? (if you can try this)

[marcosdsanchez]

➜  ~ crystal -v
Crystal 0.20.1 (2016-12-06)
➜  ~ crystal test2.cr 
35
➜  ~ crystal test2.cr --release
35

➜  ~ pacman -Q llvm-libs
llvm-libs 3.9.0-3
➜  ~ uname -a
Linux marcos-macbook-arch 4.4.36-1-lts #1 SMP Fri Dec 2 14:35:21 CET 2016 x86_64 GNU/Linux

[asterite]

Closing as duplicate of #4104