[llvm-bugs] [Bug 33795] New: [AVX512] incorrect register in vpbroadcastb instruction

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Jul 14 15:04:06 PDT 2017


            Bug ID: 33795
           Summary: [AVX512] incorrect register in vpbroadcastb
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: babokin at gmail.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 18794
  --> https://bugs.llvm.org/attachment.cgi?id=18794&action=edit

clang trunk, x86 (32 bit mode).

Clang generates "vpbroadcastb    %ch, %xmm1" instruction (at least it intends
doing so). The instruction consumes 8 bit from general purpose register, but
only 32 registers are allowed. As a result, clang tries to encode
"vpbroadcastb    %ch, %xmm1" as 62 f2 7d 08 7a cd, which really is
"vpbroadcastb %ebp,%zmm1".

I assume instruction description is incorrect.

The instruction was generated by "Machine Instruction Scheduler on function"
pass, if this matters.

Reproducer isn't really small, check "run" file for instruction for compiling
it, they should be self explanatory.

Let me know if more details are needed.

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