[llvm-bugs] [Bug 51717] New: [AMDGPU][MC][GFX10] GLOBAL and FLAT atomics discard dlc modifier

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51717

            Bug ID: 51717
           Summary: [AMDGPU][MC][GFX10] GLOBAL and FLAT atomics discard
                    dlc modifier
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: AMDGPU
          Assignee: unassignedbugs at nondot.org
          Reporter: d-pre at mail.ru
                CC: llvm-bugs at lists.llvm.org

GLOBAL and FLAT atomics accept dlc modifier but it is silently discarded. 

An example:

    flat_atomic_add v[1:2], v2
    flat_atomic_add v[1:2], v2 dlc

Both instructions are assembled into the same code with zero dlc bit:

    0x00,0x00,0xc8,0xdc,0x01,0x02,0x7d,0x00

AMD documentation does not describe any limitations on use of dlc with atomics
so the questions are:

    1. Is dlc discarded on purpose?
    2. If yes, should validator be corrected to trigger an error for atomics
with dlc?

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