[llvm-bugs] [Bug 36254] New: LLVM trunk generates AVX512BW instructions on KNL architecture

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36254

            Bug ID: 36254
           Summary: LLVM trunk generates AVX512BW instructions on KNL
                    architecture
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: wenzel.jakob at epfl.ch
                CC: llvm-bugs at lists.llvm.org

After upgrading to the latest trunk, I've noticed that LLVM sometimes generates
instructions AVX512BW instructions for the -march=knl target. These naturally
cause the application to fail. See e.g. the following LLDB trace, where a
"kmovd" instruction appears. This instruction should never be emitted, as it is
not part of AVX512F/ER/CD.

Process 161252 launched: '/home/wjakob/mitsuba2/dist/mitsuba2' (x86_64)
Process 161252 stopped
* thread #1, name = 'mitsuba', stop reason = signal SIGILL: illegal instruction
operand
    frame #0: 0x0000000041b1a5f6
libmitsuba-core.so`mitsuba::RadicalInverse::eval_scrambled(unsigned long,
enoki::Packet<unsigned long, 16ul, false, (enoki::RoundingMode)4>) const + 182
libmitsuba-core.so`mitsuba::RadicalInverse::eval_scrambled:
->  0x41b1a5f6 <+182>: kmovd  dword ptr [rsp + 0x24], k1
    0x41b1a5fd <+189>: vptestmq k1, zmm3, zmm3
    0x41b1a603 <+195>: kmovd  dword ptr [rsp + 0x20], k1
    0x41b1a60a <+202>: vpbroadcastq zmm1, rcx

The application that causes this is unfortunately very large, so I hope that
this trace is helpful enough to look for a potential cause.

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