[llvm-bugs] [Bug 43607] New: [AMDGPU][MC][GFX9] Incorrect handling of v_cndmask_b32_sdwa with src0=vcc_lo

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43607

            Bug ID: 43607
           Summary: [AMDGPU][MC][GFX9] Incorrect handling of
                    v_cndmask_b32_sdwa with src0=vcc_lo
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: AMDGPU
          Assignee: unassignedbugs at nondot.org
          Reporter: dpreobrazhensky at luxoft.com
                CC: llvm-bugs at lists.llvm.org

An example of a failed test:

    v_cndmask_b32_sdwa v5, vcc_lo, v2, vcc dst_sel:DWORD
dst_unused:UNUSED_PRESERVE src0_sel:DWORD src1_sel:DWORD

This code violates constant bus restrictions because it uses 2 scalar registers
with a partial intersection. However assembler does not detect this violation
and instead produces the following (invalid) code:

    v_cndmask_b32_sdwa v5, v2, vcc, vcc  dst_sel:DWORD
dst_unused:UNUSED_PRESERVE src0_sel:DWORD src1_sel:DWORD

This may look like a minor issue but it affects GFX10 where the provided
example should trigger no errors.

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