[llvm-bugs] [Bug 38803] New: AVX-512: Unable to copy EFLAGS physical register!

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38803

            Bug ID: 38803
           Summary: AVX-512: Unable to copy EFLAGS physical register!
           Product: clang
           Version: 7.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mgorny at gentoo.org
                CC: llvm-bugs at lists.llvm.org

Created attachment 20817
  --> https://bugs.llvm.org/attachment.cgi?id=20817&action=edit
tab.cpp

We've got a bug report from one of our users attempting to build Chromium using
clang.  The build is failing for him with the following error message:

fatal error: error in backend: Unable to copy EFLAGS physical register!
x86_64-pc-linux-gnu-clang++: error: clang frontend command failed with exit
code 70 (use -v to see invocation)


I'm attaching a minimal test case prepared by Sergei Trofimovich:

  // $ clang++ -march=skylake-avx512 -O2 tab.cpp
  // fatal error: error in backend: Unable to copy EFLAGS physical register!
  bool a();
  int b, c;
  float d;

  float fn2() {
    int e = a();
    double f = e ? 0.75f : 0;
    if (c)
      d = e ? 0 : b;
    return f;
  }

I was able to reproduce the issue with today's LLVM+Clang trunk.

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