[LLVMdev] Mips's MicroMips ??

[Daniel Sanders]

Hi,

I've had a quick look through MipsDisassembler.cpp and it seems that the disassembler doesn't know anything about 16-bit instructions at the moment. The two main problems are that DecoderTableMicroMips16 (which contains ADDU16_MM) is never used, and the disassembler always reads the opcode as a 4-byte value.

Vladimir/Sasa/Jozef/Zoran: I don't know much about the microMIPS encodings at the moment. Do you have the details on distinguishing 16-bit from 32-bit instructions?
________________________________
From: Jun Koi [junkoi2004 at gmail.com]
Sent: 29 October 2014 14:46
To: Daniel Sanders
Cc: llvmdev at cs.uiuc.edu
Subject: Mips's MicroMips ??

Hi,

We have this line in micromips-16-bit-instructions.s

    # CHECK-EB: addu16  $6, $17, $4     # encoding: [0x07,0x42]

However, when I check this with llvm-mc, like below, I dont get back the assembly.
This is against the latest LLVM code. What is wrong here?

Thanks,
Jun


$ echo "0x07,0x42"|./Release+Asserts/bin/llvm-mc -disassemble -triple=mips -show-encoding -mattr=micromips
    .text
<stdin>:1:1: warning: invalid instruction encoding
0x07,0x42
^
<stdin>:1:6: warning: invalid instruction encoding
0x07,0x42

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