[llvm-bugs] [Bug 51251] New: [MIPS] Many MIPS16 instructions are not recognized

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51251

            Bug ID: 51251
           Summary: [MIPS] Many MIPS16 instructions are not recognized
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: jesse.a.deguire at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

Created attachment 25082
  --> https://bugs.llvm.org/attachment.cgi?id=25082&action=edit
Test asm file containing every MIPS16 instruction

It would appear that LLVM does not recognize many MIPS16 instructions.

The attached assembly file is a test I made that contains, as far as I can
tell, every MIPS16 instruction. I can build it with GCC 9.3 without any issues
using the following command on Ubuntu 20.04 64-bit (Windows 10 WSL).

    mipsel-linux-gnu-gcc -march=mips32r2 -mips16 <source> -o <obj file>

However, trying to build it with Clang or LLVM-MC fails with many "instruction
requires a CPU feature not currently enabled" or "invalid operand for
instruction" errors. I have not yet verified that the instructions that do not
cause errors are correctly encoded, but a cursory look suggests that they are
not (they might be using the MIPS32 forms instead).

    llvm-mc -arch=mipsel -mcpu=mips32r2 -mattr=+mips16 -show-encoding
-show-inst <source>
    --OR--
    clang -target mipsel-linux-gnu-musl -march=mips32r2 -mips16 -c <source> -o
<obj file>

I cloned and built my version of LLVM and Clang on 27 July, 2021; however, I
believe this issue has been present for a long time. It is present on LLVM 10
that is available on Ubuntu 20.04.

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