[llvm-bugs] [Bug 37712] New: [AVX512] Incorrect disassembly for EVEX-encoded instructions

via llvm-bugs llvm-bugs at lists.llvm.org
Wed Jun 6 10:32:23 PDT 2018


            Bug ID: 37712
           Summary: [AVX512] Incorrect disassembly for EVEX-encoded
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: maks at fb.com
                CC: llvm-bugs at lists.llvm.org

To reproduce:

$ echo 'vgatherqps 0x0(%r13,%zmm4,1),%ymm5{%k2}' | llvm-mc -assemble
-arch=x86-64 -show-encoding -x86-asm-syntax=att -mcpu=knl
        vgatherqps      (%r13,%zmm4), %ymm5 {%k2} # encoding:
$ echo '0x62,0xd2,0x7d,0x4a,0x93,0x6c,0x25,0x00' | llvm-mc -disassemble
-arch=x86-64 -show-encoding -x86-asm-syntax=att -mcpu=knl
        vgatherqps      (%r13,%ymm3), %ymm5 {%k2} # encoding:

Notice the change from %zmm4 to %ymm3. Seems like decoding of VSIB index
register is broken.

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