Re: [Qemu-devel] [PATCH 4/7] tcg/mips: Support r6 JR encoding

[James Hogan <james.hogan@imgtec.com>]

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Hi Richard,

On Thu, Oct 01, 2015 at 06:49:11AM +1000, Richard Henderson wrote:
> On 10/01/2015 01:30 AM, James Hogan wrote:
> > MIPSr6 encodes JR as JALR with zero as the link register, and the pre-r6
> > JR encoding is removed. Update TCG to use the new encoding when built
> > for r6.
> >
> > We still use the old encoding for pre-r6, so as not to confuse return
> > prediction stack hardware which may detect only particular encodings of
> > the return instruction.
> >
> > Signed-off-by: James Hogan <james.hogan@imgtec.com>
> > Cc: Richard Henderson <rth@twiddle.net>
> > Cc: Aurelien Jarno <aurelien@aurel32.net>
> > ---
> >   tcg/mips/tcg-target.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/tcg/mips/tcg-target.c b/tcg/mips/tcg-target.c
> > index 4305af967326..0a16140b1cdb 100644
> > --- a/tcg/mips/tcg-target.c
> > +++ b/tcg/mips/tcg-target.c
> > @@ -288,7 +288,7 @@ typedef enum {
> >       OPC_SRLV     = OPC_SPECIAL | 0x06,
> >       OPC_ROTRV    = OPC_SPECIAL | (0x01 <<  6) | 0x06,
> >       OPC_SRAV     = OPC_SPECIAL | 0x07,
> > -    OPC_JR       = OPC_SPECIAL | 0x08,
> > +    OPC_JR_R5    = OPC_SPECIAL | 0x08,
> >       OPC_JALR     = OPC_SPECIAL | 0x09,
> >       OPC_MOVZ     = OPC_SPECIAL | 0x0A,
> >       OPC_MOVN     = OPC_SPECIAL | 0x0B,
> > @@ -322,6 +322,9 @@ typedef enum {
> >       OPC_SEH      = OPC_SPECIAL3 | 0x620,
> >   } MIPSInsn;
> >
> > +/* MIPS r6 doesn't have JR, JALR should be used instead */
> > +#define OPC_JR (use_mips32r6_instructions ? OPC_JALR : OPC_JR_R5)
> 
> This could be done in the enum instead of a define, but otherwise,

True, I'll do that.

Thanks
James

> 
> 
> Reviewed-by: Richard Henderson <rth@twiddle.net>
> 
> 
> r~
> 
> 

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