[Bug 1909838] Re: gcc -O3 produces invalid code

[Douglas Miller]

Turns out, this is due to the programmer's assumption that fcb->name[8]
and fcb->ext[3] can be accessed contiguously by fcb->name[0..10]. So,
the code is actually "lazy", if not bad. Obviously, this has worked in C
for a long time but no longer can be depended on.

** Changed in: gcc-9 (Ubuntu)
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/1909838

Title:
  gcc -O3 produces invalid code

Status in gcc-9 package in Ubuntu:
  Invalid

Bug description:
  If I compile the attached file with -O3, gcc produces an empty
  function (simply returns 0). If I compile without -O3, gcc produces
  viable code that functions as expected.

  Linux outhouse 5.4.0-58-generic #64-Ubuntu SMP Wed Dec 9 08:16:25 UTC
  2020 x86_64 x86_64 x86_64 GNU/Linux

  gcc  4:9.3.0-1ubuntu2

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