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Date:   Thu, 20 Jun 2013 16:40:59 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@linux-mips.org>
To:     Ralf Baechle <ralf@linux-mips.org>
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Subject: Re: [PATCH UPDATED 4/4] MIPS: Move definition of SMP processor id
 register to header file
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On Thu, 20 Jun 2013, Ralf Baechle wrote:

> So I've removed it again for now.
> 
> Maciej, I wonder why does gas in MIPS III/IV mode accept
> 
> 	dmfc0	$reg1, $cp0reg
> 
> but not
> 
> 	dmfc0	$reg1, $cp0reg, 0
> 
> The generated code is the same after all.  Same for MIPS I/II mode and 
> mfc0.

 The <sel> operand and instruction field was only added to these 
instructions with the MIPS64 ISA (MIPS32 ISA for MFC0/MTC0).  Previously 
processors did not decode this field and consequently the assembler 
notation only supports two operands.

 Since AFAICT the offending pieces are macros I suggest simply dumping the 
redundant ", 0" part, the two-argument form is as you've observed 
equivalent.

  Maciej