[Bug 1815057] Re: [UBUNTU] GCC Wrong code generate for floating point workloads Ubuntu 18.04

[Dimitri John Ledkov]

This is fixed in disco.

Just to manage expectations, as we do full-archive rebuilds across all
architectures upon toolchain point release updates, landing these
backports will take... a while.

Hopefully this will be released for both bionic & cosmic by end of year.

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Title:
  [UBUNTU] GCC Wrong code generate for floating point workloads Ubuntu
  18.04

Status in Ubuntu on IBM z Systems:
  In Progress
Status in gcc-7 package in Ubuntu:
  Fix Released
Status in gcc-8 package in Ubuntu:
  Fix Released
Status in gcc-7 source package in Bionic:
  New
Status in gcc-8 source package in Bionic:
  New
Status in gcc-7 source package in Cosmic:
  New
Status in gcc-8 source package in Cosmic:
  New

Bug description:
  An IBM Z GCC backend problem leads to wrong code being generated for
  some floating point workloads.

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88856

  A patch has been committed to the GCC 7 and 8 upstream branch and
  needs to be picked up for the Ubuntu 18.04 compiler.

  https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=268551

  This change might require rebuilding floating point related packages.
  Although the actual problem is hard to trigger. I could only reproduce
  it in case if conversion introduces load on condition instructions in
  the ce2 pass. The testcase I've looked into came from the python scipy
  package which builds with -funroll-loops. The load on condition
  opportunity in that case was introduced with the RTL loop unrolling.
  This made the split1 pass to use the problematic splitter generating
  wrong code in the end.

  According to https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=915738

  The patch has been picked up for gcc-8 8.2.0-18 already

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